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2022 Fall Meeting

Functional materials


Phase transitions and properties of ferroics in the form of single crystals, ceramics and thin films II

Ferroic materials undergo a large variety of phase transitions and also exhibit important physical properties, many of which are used in industries world-wide. The study of their phase transitions provides useful ways to understand the origin of the properties, and thus to suggest new materials. Functionality in ferroics can be considered independently on their sizes. They are functional in the macroscopic, microscopic and nanoscopic scales in the form of single crystals, ceramics and thin films. Additionally, the role of controlled content of defects and hence the surface-bulk interrelation makes these materials scientifically exciting and perspective.


Ferroics exhibit strong changes in their properties at a phase transition between a high-symmetry phase, where the material is in a non-ferroic state, and a low-symmetry phase, where the shape of the unit-cell is slightly altered. This breaking of symmetry leads to the appearance of a new physical quantity that can be switched in some way. For instance, the oldest known ferroic property is that of ferromagnetism where magnetization can be switched by an applied magnetic field, leading to magnetic hysteresis. By analogy with ferromagnetism, ferroelectrics are where an electric polarization is switched by an applied electric field, again with hysteresis; and ferroelastics are where strain is switched by an applied stress. These ferroics are known as primary ferroics. One can also have multiferroics where two or more such ferroic properties are present, e.g. magnetization can be switched by an applied electric field, and vice versa. It can be appreciated therefore that ferroics provide a rich field of materials with interesting properties and behaviour, many of which have very important industrial use.

Group-subgroup symmetry changes at phase transitions often define the properties of ferroics. However, changes in micro- and nano-structures are at least as important. It is possible to tune both by changing the form of the material: single crystal, ceramic or thin film. This led to major breakthroughs such as the discovery of unexpected phases and properties at interfaces, as well as giant responses and phase transitions induced by light or electric field. The recent interest for topological structures in ferroics, e.g. domain walls, vortexes, skyrmions, which exhibit their own functionalities and properties, brings a new playground which makes ferroic materials even more scientifically exciting. The symposium will bring together experts working at the theoretical and experimental level.

Hot topics to be covered by the symposium:

  • Structural phase transitions and critical phenomena
  • Magnetoelectric and multiferroic materials
  • Topological structures, domain boundary engineering
  • Interfacial properties, 2D gases
  • Thin films, multilayers and heterostructures
  • Advances in ab-initio calculations and experimental methods
  • Electro/magneto/mechano-caloric effects
  • Flexoelectricity
  • Piezotronics and photo-piezotronics
  • Integration and devices
  • Light-induced phenomena
  • Defects and disorder in ferroics
  • Electronic structure and optical properties
  • Ferroelectrics and antiferroelectrics
  • Piezoelectrics and lead-free piezoelectrics
  • Relaxors and applications
  • Recent advances in electron microscopic study of atomic arrangements
  • Structural aspects of photovoltaic perovskites, organic-inorganic photovoltaic materials

Invited speakers:

  • O. Aktas – Xi'an Jiaotong University, China
  • S. Artyukhin – Italian Institute of Technology, Genova, Italy
  • M. Bibes – Unité Mixte de Physique CNRS/Thales, Palaiseau, France
  • A. Bussmann-Holder – Max-Planck Institute, Stuttgart, Germany
  • D. Damjanovic – Ecole Polytechnique Federale de Lausanne, Switzerland
  • O. Dieguez – Tel Aviv University, Israel
  • B. Dkhil – Ecole Centrale Paris, France
  • M. Trassin – ETH Zürich, Switzerland
  • S. Gorfman – Tel Aviv University, Israel
  • M. Ghidini – University of Parma, Italy
  • P. Ghosez – CESAM, Université de Liège, Belgium
  • M. Gregg – Queen’s University of Belfast, N. Ireland (UK)
  • M. Guennou – University of Luxembourg, Luxembourg
  • J. Hlinka – Czech Academy of Sciences, Prague, Czech Republic
  • S. Gonzalez – Institut des Nanotechnologies de Lyon, France
  • J. Iniguez – Luxembourg Institute of Sciences and Technology, Luxemburg
  • S. Kamba – Czech Academy of Sciences, Prague, Czech Republic
  • A. Klein – TU Darmstadt, Germany
  • J. Koruza – TU Darmstadt, Germany
  • M. Mączka – Polish Academy of Sciences, Wrocław, Poland
  • T. Rojac – Josef Stefan Institute, Ljubljana, Slovenia
  • W. Schranz – University of Wien, Austria
  • J. Schultheiss - Norwegian University of Science and Technology, Norway
  • C. Toulouse – University of Luxembourg, Luxembourg
  • R. McQuaid – Queen's University Belfast, N. Ireland (UK)
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Session 9:00 - 10:30 : Chair - Mike Glazer
Authors : J. M. Gregg
Affiliations : Queen's University Belfast

Resume : Partial switching of ferroelectric lithium niobate thin films causes the injection of 180 degree domain walls which are initially strongly inclined with respect to the polarisation axis. Strong inclination angles mean a significant polar discontinuity across the domain wall that is associated with dramatically enhanced electrical conductivity. In the first part of this talk, the magnetotransport behaviour of these conducting walls will be reported. The naturally formed conical domain structures allow for geometrical magnetoresistance behaviour analogous to that seen in Corbino Discs, allowing direct access to carrier mobility values. Such mobilities are extremely large - of the order of thousands of cm2V-1s-1. We believe them to be the highest room temperature values seen in any oxide system to date. In the second part of the talk, the manner in which domain wall morphology and conductance can be altered by applied fields and wall relaxation after field removal will be presented. It will be shown that complex kinetics and associated conduction variations allow for both neuromorphic and conventional memory-related functionality to be generated.

Authors : Kostyrko M., Vasylkiv Yu., Adamenko D., Skab I. and Vlokh R.
Affiliations : O.G. Vlokh Institute of Physical Optics, 23 Dragomanov Str. Lviv, Ukraine, 79005,

Resume : Optical vortices operation with using of single ferroic crystals via parametrical optic effects Kostyrko M., Vasylkiv Yu., Adamenko D., Skab I. and Vlokh R. O.G. Vlokh Institute of Physical Optics, 23 Dragomanov Str. Lviv, Ukraine, 79005, The possibility of generation of the optical vortices with the help of parametric optic effects in single crystals under the action of inhomogeneous mechanical stresses, electric field, and at the acousto-optic interaction is demonstrated. On the basis of analysis of polarization topological defects (TDs) that appear at the torsion of crystals, it has been found that in the crystals that possess 3-fold symmetry axes the torsion stresses lead to the appearance of the single charged optical vortex (OV). The appearance of OV with the unitary charge has been experimentally proved at the torsion of LiNbO3 and Pb5Ge3O11 ferroelectric crystals. It has been shown that operation by the efficiency of spin-to-orbit angular momentum conversion is carried out by the change of torsion moment. It has been found that mechanical bending of crystalline or glass samples leads to the appearance of TDs in the emerging beam, which in the general case leads to inducing screw-edge dislocation of the wavefront. On the basis of phenomenological analysis and experimental study of the polarization TDs, induced by an inhomogeneous electric field in crystals it is established that for the acentric crystals the electric field of conical configuration leads to the appearance of pure screw dislocation of the optical wavefront and the emergent beam should bear the OV with the unitary topological charge. Such OV was experimentally revealed in the LiNbO3 and Bi12GeO20 crystals. It has been shown that the efficiency of spin-to-orbit momentum conversion can be operated by the electric field in crystals, while the double-charged optical vortices can be generated with the help of the Kerr electro-optic effect. The behavior of TDs of optical indicatrix orientation induced by a conically shaped electric field in crystals in a crossover regime that appears at intermediate fields separating the regimes of prevailing Pockels and Kerr electro-optic nonlinearities is analyzed. The processes of birth, addition, decay, and annihilation of the TDs of optical indicatrix orientation are observed under varying electric field. We have experimentally shown for the first time that the intensity profile and the phase structure of the vortex beam are preserved under acousto-optic Bragg diffraction. As a result, the OV beam can be deflected due to acousto-optic diffraction, whereas the acousto-optically operated OV beams can be efficiently used in such novel branches of optical technology as optical trapping and controlled addressing of the beams with different orbital angular momentums. Generation of an array of OVs with fractional charges under the conditions of acousto-optic Bragg diffraction is revealed experimentally.

Authors : Jiří Hlinka
Affiliations : Institute of Physics, Czech Acad.Sci.

Resume : Skyrmions and Skyrmion textures in magnets are now subjects of well established research and technology disciplines. On the other hand, the perspectives of their electric analogues have only recently been approached. Here we would like to draw the attention to the symmetry-breaking species, and to advocate for the search of new families of materials allowing the direct ferroelectric analogue of the bulk magnetic DMI.

10:30 Coffee break    
Session 11:00 - 12:30 : Chair - Jiří Hlinka
Authors : Oswaldo Diéguez, Massimiliano Stengel
Affiliations : Oswaldo Diéguez [1, 2] ; Massimiliano Stengel [3, 4] [1] Department of Materials Science and Engineering, Faculty of Engineering, Tel Aviv University, Tel Aviv 6997801, Israel [2] Theory and Simulation Group, Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC, BIST, Campus UAB, Bellaterra, Barcelona 08193, Spain [3] Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus UAB, 08193 Bellaterra, Spain [4] ICREA - Institució Catalana de Recerca i Estudis Avançats, 08010 Barcelona, Spain

Resume : Macroscopic descriptions of ferroelectrics have an obvious appeal in terms of efficiency and physical intuition. Their predictive power, however, has often been thwarted by the lack of a systematic procedure to extract the relevant materials parameters from the microscopics. We address this limitation by establishing an unambiguous two-way mapping between spatially inhomogeneous fields and discrete lattice modes. This yields a natural treatment of gradient couplings in the macroscopic regime via a long-wavelength expansion of the crystal Hamiltonian. Our analysis reveals an inherent arbitrariness in both the flexoelectric and polarization gradient coefficients, which we ascribe to a translational freedom in the definition of the polar distortion pattern. Remarkably, such arbitrariness cancels out in all physically measurable properties (relaxed atomic structure and energetics) derived from the model, pointing to a generalized translational covariance in the continuum description of inhomogeneous ferroelectric structures. We demonstrate our claims with extensive numerical tests on 180-degree domain walls in common ferroelectric perovskites, finding excellent agreement between the continuum model and direct first-principles calculations.

Authors : Tadej Rojac, Mirela Dragomir, Mojca Otonicar
Affiliations : Jozef Stefan Institute, 1000 Ljubljana, Slovenia

Resume : Lead-based relaxor ferroelectrics, exemplified by the Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) solid solution, are the best performing multifunctional materials among its class. Despite several decades of investigations, however, the large piezoelectric response of PMN-PT and similar relaxor-based materials is still subject of debates with a number of different, often incompatible microscopic mechanisms that have been proposed so far to explain the large response. In particular focus is the dynamic role of the so-called low-angle domain walls, which are formed in the PMN-richer compositions due to their disordered polar structure and relaxor behavior. In this contribution, I will try to shed light on this issue by presenting systematic data on the nonlinear and hysteretic converse piezoelectric response of PMN-PT ceramics in a wide compositional range, covering the relaxor monoclinic phases at low PT contents, to morphotropic and tetragonal ferroelectric compositions at higher PT contents. Harmonic analysis reveals a unique nonlinear behavior confined to a large portion of the monoclinic phase region in the PMN-PT phase diagram. This particular nonlinear hysteretic and anyhsteretic response is not observed in normal ferroelectric Pb(Zr,Ti)O3 (PZT) in which the relaxor features are absent. I will try to provide a link between this response and the compositional-dependent multiscale structure of PMN-PT, including the atomic-scale structure probed by scanning transmission microscopy (STEM) techniques. The results confirm the key role of the dynamics of low-angle domain walls in a wide compositional range in PMN-PT going well beyond morphotropic compositions.

Authors : Hiroko Yokota, Zheyi An, Kyomaru Kurihara, Nozomu Hasegawa, Nan Zhang, Marek Pa?ciak, A. M. Glazer
Affiliations : Chiba Univ., JST PRESTO; Xi?an Jiaotong Univ.; Institute of Physics of the Czech Academy of Sciences,; Oxford Univ., Warwick Univ.

Resume : Domain boundaries have become one of the hot topics in ferroics and many unique physical properties which are different from bulk have been reported. Although ferroics contain different types of boundaries, most studies are focused on ferroelastic domain boundaries. It is not surprising the same phenomena would also exist in other types of boundaries. Here, we investigated antiphase boundaries (APBs) which separate neighbouring domains with phase shifts while do not interrupt the crystallographic distortion of the bulk. We chose antiferroelectric PbZr0.98Ti0.02O3 (PZT) single crystal and performed nonlinear second harmonic generation microscope (SHGM) observations and diffuse scattering experiments. These results indicate that APBs in PZT single crystal possesses a polar nature. Under the application of stress, the SH intensity becomes several times larger than the virgin state which suggests the enhancement of polarity at APBs. Combining with the calculation, we identify the nature of polarity at the APBs in PZT.

12:30 Lunch    
Session 14:00 - 15:30 : Chair - Hiroko Yokota
Authors : Semën Gorfman 1, David Spirito 1, Guanjie Zhang 2, Carsten Detlefs 3, Nan Zhang 2
Affiliations : 1 Department of Materials Science and Engineering, Faculty of Engineering, Tel Aviv University, Tel Aviv, Israel 2 Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education and International Center for Dielectric Research, School of Electronic and Information Engineering, Xi'an, China 3 European Synchrotron Radiation Facility, Grenoble, France

Resume : Formation of domains is ubiquitous in any ferroic (ferroelectric, ferroelastic or ferromagnetic) crystals. For example, the tessellation of the crystal space into complex pallets of ferroelastic (= strain) domains occurs at the phase transition, changing the crystal system (e.g. from cubic to tetragonal, rhombohedral to monoclinic, etc.). Once formed, domain patterns stand behind many exotic and functionally important materials properties, such as shame-memory effect, superelasticity and giant electromechanical activity. These properties are especially bold when domains host several order parameters at the same time such as spontaneous polarization. All the aspects, related to the domains formation and domains dynamics attract the interest of broad communities of researchers. Unfortunately, however, despite such great interest, there is still a lack of experimental techniques, for non-destructive characterization of domain patterns. The aim of this work is to advance high-resolution single crystal X-ray diffraction for the understanding of ferroelastic domain patterns. Compared to the existing techniques (e.g. transmission electron, optical or piezo-response microscopies), X-ray diffraction offers essential benefits of sensitivity to the lattice parameters and reaching material bulk. We develop the theoretical framework and a computer program, which predicts the separation between Bragg peaks diffracted from mechanically matched ferroelastic domains. The major hypothesis behind this program is mechanical compatibility between ferroelastic domains, e.g. meeting along a lattice a plane that has identical two-dimensional lattice parameters. We derive all the necessary equations and outline an algorithm for the calculation of the separation between the Bragg peaks, diffracted from possible coherent twin domains, connected to one another via mismatch-free interface. We demonstrate that such separation is always perpendicular to the planar interface between the matched domains. For illustration purposes, we present the analysis of the separation between the peaks diffracted from tetragonal and rhombohedral domains in the high-resolution reciprocal space maps of BaTiO3 and PbZr1-xTixO3 crystals. The demonstrated method can be used to analyse the response of multi-domain patterns to external perturbations such as electric field, change of temperature or pressure.

Authors : J. Schultheiss
Affiliations : Department of Materials Science and Engineering, NTNU Norwegian University of Science and Technology, 7034, Trondheim, Norway

Resume : In hexagonal manganites, ferroelectricity arises as a symmetry-enforced by-product of a structurally driven phase transition. As a consequence, the materials exhibit a large variety of unusual physical phenomena, ranging from domain walls with unique electronic properties to topological vortex structures that have been utilized to test cosmological scaling laws. Most research, however, has focused on single crystals and thin films, whereas only few studies were performed on polycrystalline systems. In particular, the impact of the microstructure on the ferroelectric domain distribution remains to be explored. Here, I present a systematic study on the impact of varying grain size on the domain structure, utilizing polycrystalline ErMnO3 as a model system. In contrast to proper ferroelectrics, such as BaTiO3 and Pb(Zr,Ti)O3, an inverted scaling behavior is observed, leading to the formation of smaller domains in larger grains. The unusual scaling behavior is related to topologically protected vortices that naturally form in the ferroelectric phase of ErMnO3 and their interaction with elastic strain fields. This interaction of elastic strain and topological defects is intriguing as it provides a conceptually new handle for tuning the electromechanical and dielectric performance of ferroelectrics, giving a new dimension to capacitor applications and domain wall-based nanoelectronics.

Authors : Morgan Trassin
Affiliations : Department of Materials, ETH Zurich

Resume : In ferroelectric thin films, the polarization state, i. e. polarization orientation and domain architecture, defines the macroscopic ferroelectric properties such as the switching dynamics. Ferroelectric domain engineering is therefore a key for the development of low energy consuming oxide electronics. Here we show how nonlinear optics can enable the in-situ investigation of the ferroelectric polarization in ultra-thin ferroelectric films during the growth. Beyond the unprecedented access to the emergence of ferroelectricity and domain formation during the epitaxial deposition, we investigate transient polarization states originating from the evolving charge-screening environment of the oxide thin film growth process. We show the impact of lattice chemistry, depolarizing field-related effects in-situ and identify routes towards the establishment of robust polarization states in the ultrathin regime. Our work provides new insights dealing with the physics of ultrathin ferroelectrics and further control of ferroelectric-based heterostructure.

15:30 Coffee break    
Session 16:00 - 17:30 : Chair - Jan Schultheiss
Authors : S. Gonzalez (1), P. Rojo-Romeo (2), M. Bugnet (3), P. Schöffmann (4), E. Otero (4), B. Vilquin (2), N. Baboux (1), B. Gautier (1), G. Herrera (5), O. Boisron (5), D. Le Roy (5), F. Tournus (5), P. Ohresser (4), V. Dupuis (5), I. C. Infante (1)
Affiliations : 1 Univ. Lyon, INSA Lyon, CNRS, ECL, UCBL, CPE Lyon, Institut des Nanotechnologies de Lyon, UMR5270, 69621 Villeurbanne, France -; 2 Univ. Lyon, ECL, CNRS, CPE Lyon, Institut des Nanotechnologies de Lyon, UMR5270, Ecully, France; 3 Univ. Lyon, CNRS, INSA Lyon, UCBL, MATEIS, UMR 5510, 69621 Villeurbanne, France; 4 Synchrotron SOLEIL, CNRS-CEA, L’Orme des Merisiers, Saint-Aubin, 91192 Gif-sur-Yvette, France; 5 Univ Lyon, Université Claude Bernard Lyon 1, Institut Lumière Matière, CNRS UMR 5306, France

Resume : Nano ferroelectricity has promising technological applications as energy-saving, low-sized electronic devices. Tunnel junctions and transistors using ferroelectric gates are examples of potential applications [1]. BaTiO3 (BTO) is a lead-free ferroelectric showing fascinating properties when connected to an electrode, in particular a “positive dead-layer” [2] or interface ionic relaxation [3], making BTO a promising candidate for integration in multifunctional structures with ultimate nanoscale dimensions. For this purpose, the physical and chemical properties of interfaces and ultrathin layers based on BTO have to be understood and means to control their properties must be sought out. In this work, we propose to study ultrathin BTO films grown by industrially scalable magnetron sputtering on conductive Nb-doped SrTiO3 substrates and on structurally compatible conductive layers of SrRuO3, with capping electrodes defining BTO-capacitors, to explore the effect of the conduction and chemical reconstruction phenomena within the films and at the different interfaces. The average structure and strain of BTO films from 2 to 16 nm were investigated using X-ray diffraction. A thorough spectroscopic analysis of the films was carried out to study the relationship between strain and materials and processing parameters. Combining synchrotron X-ray absorption spectroscopy in capacitors and laboratory X-ray photoelectron spectroscopy, we probed the electronic structure under the influence of different UHV annealing conditions, studied the promotion of electronic and ionic defects, e.g. oxygen vacancies. Structural and polarization states of differently strained BTO films were analyzed through X-ray natural linear dichroism at the Ti-L2,3 edges. Multiplet calculations were made, supporting the experimental evidence of the contribution of the strain to the polarization of the films. Finally scanning transmission electron microscopy and electron energy loss electron spectroscopy provided the atomic scale evidences of the electronic structure through the films and at the interfaces. These results are crucial to understand and master the underlying physical mechanisms leading to the ferroelectric properties of operating BTO-based devices. This work is supported by collaborative VOLCONANO ANR-19-CE09-0023 project. [1] Scott, J.F. Science 315, 954 -959 (2007) [2] Stengel, M., Vanderbilt, D. & Spaldin, N.A. Nature Materials 8, 392-397 (2009). [3] Gerra G., Tagantsev A. K., and Setter N., Physical Review Letters 98, 207601 (2007).

Authors : Sabine Körbel
Affiliations : Institute of Solid State Theory and Optics, Friedrich Schiller University of Jena, Germany

Resume : The photovoltaic effect in BiFeO3 has been suggested to involve separation of photogenerated electron-hole pairs by ferroelectric domain walls. Ab initio calculations indicate that, similar to the case of Fe2O3 [1,2], excess electrons in BiFeO3 form small polarons with electronic levels several tenths of an eV below the conduction band minimum [3]. We find that these small polarons tend to accumulate at ferroelectric domain walls [4]. I will present evidence from first-principles modeling suggesting that photogenerated electron-hole pairs, similar to excess electrons alone, also form small polarons at the ferroelectric domain walls, and that this process impedes charge-carrier separation [5]. [1] C. Lohaus et al., "Limitation of Fermi level shifts by polaron defect states in hematite photoelectrodes", Nature Communications 9, 1-7 (2018) [2] H. Peng & S. Lany, "Semiconducting transition-metal oxides based on d 5 cations: Theory for MnO and Fe2O3", Physical Review B 85, 201202 (2012) [3] A. Radmilovic et al.,"Combined Experimental and Theoretical Investigations of n-Type BiFeO3 for Use as a Photoanode in a Photoelectrochemical Cell", Chemistry of Materials 32, 3262-3270 (2020) [4] S. Körbel et al., "Electron trapping by neutral pristine ferroelectric domain walls in BiFeO3", Physical Review B 98, 100104(R) (2018) [5] S. Körbel and S. Sanvito, "Photovoltage from ferroelectric domain walls in BiFeO3", Physical Review B 102, 081304(R) (2020)

Authors : G. Magagnin, Q. Wu, D. Martinotti, E.K.H. Salje, C. Lubin, C. Paillard, G. Geneste, T. Maroutian, N.Barrett
Affiliations : SPEC, CEA, CNRS, Université Paris-Saclay, CEA Saclay, 91191 Gif-sur-Yvette, France; SPEC, CEA, CNRS, Université Paris-Saclay, CEA Saclay, 91191 Gif-sur-Yvette, France; SPEC, CEA, CNRS, Université Paris-Saclay, CEA Saclay, 91191 Gif-sur-Yvette, France; Dept. of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK; SPEC, CEA, CNRS, Université Paris-Saclay, CEA Saclay, 91191 Gif-sur-Yvette, France; Laboratoire Structures, Propriétés et Modélisation des Solides, CentraleSupélec, CNRS-UMR8580, Université Paris-Saclay, 91190 Gif-sur-Yvette, France; CEA, DAM, DIF, F-91297 Arpajon, France and Université Paris-Saclay, CEA, LMCE, 91680 Bruyères-le-Châtel, France; Université Paris-Saclay, CNRS, Centre de Nanosciences et de Nanotechnologies, 91120, Palaiseau, France; SPEC, CEA, CNRS, Université Paris-Saclay, CEA Saclay, 91191 Gif-sur-Yvette, France

Resume : In ferroic materials, domains with uniform order parameters form to minimize the total free energy. Domain walls are a trade-off between the energy cost of the wall formation and the gain from domain ordering. They break translational symmetry and can exhibit fascination properties absent in the bulk, parent structure. At the twin walls in purely ferroelastic CaTiO3, one of the octahedral tilts goes to zero allowing the emergence of polarity by off-centering of the Ti cation. This could potentially be controlled electromechanically, adding functionality to the system. The modification of the electronic structure at the intersection of the twin walls and sample surface would open up perspectives for engineering domain wall functionality. The presentation will first show the experimental and theoretical evidence of band gap narrowing in the twin walls at the surface of bulk CaTiO3 and then results on the topographic and electronic properties of the domain and domain walls in CaTiO3 thin films. Using Electron Energy Loss Spectroscopy in a low energy electron microscope (LEEM), we have simultaneously revealed the domain wall polarity in the pure ferroelastic CaTiO3 bulk crystals and surface band gap narrowing in the domain walls. The band gap reduction of the walls compared to the domains vary between 0.01 and 0.47 eV for domain wall polarity pointing out of the surface and into the bulk, respectively. Ab-initio, hybrid functional calculations support the hypothesis of a higher concentration of oxygen vacancies near the domain walls but despite the associated structural modifications they cannot explain the band gap narrowing. Indeed, the oxygen vacancies create rather localized in-gap states whereas the reduction in the gap near the domain walls is due to screening by electrons of the polar discontinuity at the surface, which can only populate states if the conduction band is lowered. As a first step to a possible functional heterostructure, we have used pulsed laser deposition to produce expitaxially compressed CaTiO3 thin films on ferroelastic LaAlO3 substrates. The strain interaction between substrate and film gives rise to complex domain wall patterns, which we analyze using both low energy and photoemission electron microscopy (PEEM).

Authors : Shuang Gao1, Changhao Zhao1, Jurij Koruza2, Hans-Joachim Kleebe1, Jürgen Rödel1
Affiliations : 1Department of Materials and Earth Sciences, Technical University of Darmstadt, 64287 Darmstadt, Germany 2Institute for Chemistry and Technology of Materials, Graz University of Technology, A-8010 Graz, Austria

Resume : Electromechanical hardening is of great significance for piezoceramics used for high-power applications [1]. Precipitation hardening has been extensively achieved in metals to strengthen their mechanical properties [2]. The state-of-the-art research demonstrates the effective implementation of precipitation hardening in piezoceramics to enhance piezoelectric properties by pinning domain wall motions with formed precipitates [3]. With the introduced plate-like LiNbO3 (LN) precipitate in Li-doped NaNbO3 (NN), the mechanical quality factor (Qm) shows a tenfold increase, which is closely related to the precipitate-domain wall interaction. TEM study revealed that LN plates habit on {110}PC planes of NN matrix with matrix-precipitate orientation relationships of [100]PC // [241]LN, (01 ̅1)PC // (2 ̅10)LN, (011)PC // (014 ̅)LN (or (011)PC // (2 ̅10)LN, (01 ̅1)PC // (014 ̅)LN) and [011]PC // [121 ̅]LN, (01 ̅1)PC // (2 ̅10)LN, (100)PC // (012)LN. Permissive 90°, 180°, 60°, and 120° domain walls in NN matrix are concluded as either {100}PC type or {110}PC type. By forming {110}PC LN precipitate plates, all permissive domain walls are effectively pinned with either intersecting or parallel precipitate-domain wall geometrical relationship. Our findings could lead to a new insight of hardening mechanism with plate-like precipitates from the perspective of precipitate-domain wall interaction and provide novel strategy for the design of piezoceramics for high-power applications. References: [1] Hardtl KH. Electrical and mechanical losses in ferroelectric ceramics. Ceram. Int. 1982; 8: 121-127. [2] Ardell AJ. Precipitation hardening. Metall. Mater. Trans. A 1985; 16A: 2131-2165. [3] Zhao CH, Gao S, Yang TN, et al. Precipitation hardening in ferroelectric ceramics. Adv. Mater. 2021; 33: 2102421.

Authors : Mauro A.P. Gonçalves, Marek Paściak, Jiří Hlinka
Affiliations : Institute of Physics of the Czech Academy of Sciences, Prague 18221, Czech Republic

Resume : Polar Skyrmions were predicted few years ago, when studied a columnar nanodomain with positive polarization within a matrix of opposed polarization in a single-phase PbTiO3 [1]. Few months later in a study, combining several experimental and theoretical methods, S. Das and colleagues [2] proved that polar Skyrmions can be stabilized at room temperature in PbTiO3/SrTiO3 superlattices. The most recent studies revealed a reversible phase transition from the skyrmion state to a trivial uniform ferroelectric state, accompanied by large tunability of the dielectric permittivity [3]. Here, we intend to answer other questions regarding polar skyrmions. Is it possible, using a similar strategy, to stabilize Skyrmions in other ferroelectric materials like BaTiO3? Will these new skyrmions be topologically like those observed earlier? Or are they formed by a different arrangement of dipoles with a different topology? To answer these questions, we used shell model potential for BaTiO3 [4] solved using molecular dynamics to study low-temperature columnar nanodomains in BaTiO3. To inspect the stability of the polar Skyrmions obtained in BaTiO3, we investigate its lattice dynamics and the effect of the external electric fields in columnar nanodomains with different sizes. Acknowledgements: This work was supported by the Czech Science Foundation (project no. 19-28594X). 1 M. A. P. Gonçalves et al., Science Advances 5, no. 2, eaau7023 (2019) 2 S. Das et al., Nature 568, 368 (2019) 3 S. Das et al., Nature Materials 20, 194–201 (2021) 4 M. Sepliarsky, Current Opinion in Solid State and Materials Science 9, 107-113 (2005)

Poster Session 17:30 - 19:30 : Guillaume Nataf & Marek Paściak & Krystian Roleder
Authors : A.A. Prokhorov1, R. Minikayev3, D.V. Savchenko1,4, J. Lan?ok1, A.D. Prokhorov2
Affiliations : 1. Institute of Physics AS CR, Na Slovance 2, 18221 Prague, Czech Republic 2. A.A. Galkin Donetsk Physico-Technical Institute, R. Luxembourg 72, 83114 Donetsk 3. Institute of Physics PAS, al. Lotnikow 32/46, 02-668, Warsaw, Poland 4. National Technical University of Ukraine ?Igor Sikorsky Kyiv Polytechnic Institute?, pr. Peremohy 37, Kyiv, 03056, Ukraine

Resume : New data about the electronic state of Tb3+ doping ions in the Tb-doped EuAl3(BO3)4 and EuGa3(BO3)4 borate single crystals have been obtained from the electron paramagnetic resonance (EPR) spectra measurements at X- and Q-band frequency range in the wide temperature interval. Prior to the EPR study, the X-ray diffraction (XRD) techniques the structural and elastic properties of Tb3+ doped EuAl3(BO3)4 and EuGa3(BO3)4 single crystals were determined at T = 300-1073 K. The following spin Hamiltonian parameters for Tb3+ ions were obtained: gz=17.064±0.019, Az=6.231±0.012 GHz, ?=7.333±0.016 GHz in EuAl3(BO3)4:Tb crystals and gz=17.664±0.011, Az=6.251±0.012 GHz, ?=3.891±0.035 GHz in EuGa3(BO3)4:Tb crystals. The temperature dependence of the EPR linewidth for Tb3+ ions in EuAl3(BO3)4:Tb and EuGa3(BO3)4:Tb crystals was described by an exponential law that is characteristic of the Aminov-Orbach processes. It was concluded that the Tb3+ ions substitute for the three-valence europium ones in EuGa3(BO3)4:Tb/ EuAl3(BO3)4:Tb crystal lattice.

Authors : K. Shanmuga Priya, Subhajit Pal, P. Murugavel
Affiliations : Pervoskites Material’s Laboratory, Functional Oxide Research Group (FORG), Department of Physics, Indian Institute of Technology Madras, Chennai, Tamil Nadu, India. School of Engineering & Materials Science, Queen Mary University of London, London, E1 4NS, United Kingdom.

Resume : Effect of external stimuli such as electric field on the ferroelectric oxide systems along with their enhanced physical properties is a fascinating topic of research.1,2 In this work, the effect of poling on the physical characteristics of photovoltaic lead-free ferroelectric Ba0.875(Bi0.5Li0.5)0.125TiO3 (BBLT) oxide is investigated. The structural properties of the BBLT sample are investigated by the X-ray diffraction and it revealed a 23% increase in orthorhombic phase fraction at the cost of a tetragonal phase upon poling. Rayleigh analysis on the polarization data recorded under sub-coercive fields suggested that the poling-induced structural phase transformation is correlated to the lattice deformation induced by the electric field. The suppression of the Bi-O bond length (A2g) under an electric field in poled sample is demonstrated by Raman spectroscopy. The field-induced orientational defect resulted in an asymmetry in the polarisation hysteresis loop with an internal bias electric field of 8 V/cm. In the dielectric studies, the increase in long-range interaction caused the decrease in dielectric dispersion for poled BBLT. Importantly, the poling induced large internal bias field of the sample facilitates the large photovoltaic response with an open-circuit voltage of 12 V. These results could open up the application potential of this system in the fields such as photovoltaic and photodetectors3,4. [1] W. Liu and X. Ren, Phys. Rev. Lett. 103, 257602 (2009). [2] B. N. Rao, R. Datta, S. S. Chandrashekaran, D. K. Mishra, V. Sathe, A. Senyshyn, and R. Ranjan, Phys. Rev. B 88, 224103 (2013). [3] Pal S, Muthukrishnan S, Sadhukhan B, Sarath N V, Murali D, and Murugavel P J. Appl. Phys. 129 084106 (2021). [4] P. P. Biswas, S. Pal, V. Subramanian, and P. Murugavel, J. Phys. D: Appl. Phys., 53, 27 (2020).

Authors : Haeun Seo, Hye-Yeong Park, Haeun Kim, Donghyun Kim, Dong Gyeong Kim, Hyeryang Choi, SeungCheol Yang
Affiliations : Department of Materials Convergence and System Engineering, Changwon National University, Changwon, Gyeonsangnam 51140, Republic of Korea

Resume : Photocurable ceramic slurries used in digital light processing (DLP) for ceramic 3D printing have been mainly composed of photocurable acrylic resins, ceramic particles and photo-initiaor. During by DLP 3D printing process, there is a problem of peeling between layers in ceramic green body due to a lack of adhesion between layers formed with photo-cured acrylic resins. In this study, we prepared epoxide based ceramic slurry by using fused silica particles, dispersants, photo/thermal initiators, and acrylate/epoxide monomers for DLP 3D printing. After that, through light irradiation and subsequent thermal polymerization, ceramic green bodies was fabricated. The ceramic green bodies showed an excellent interlayer adhesive force due to a hydroxyl group generated in a thermal polymerization of epoxide in a monomer. In addition, the fracture strength of the green body including epoxide was higher than that of acryl based green body. The fired body obtained through subsequent firing had no interlayer exfoliation.

Authors : Irena Jankowska-Sumara1, Marek Pa?ciak2, Jae-Hyeon Ko3, Andrzej Majchrowski4, Mariola K?dzio?ka-Gawe?5, Roman Burkovsky6
Affiliations : 1. Institute of Physics, Cracow Pedagogical University, Kraków, Poland 2. Institute of Physics of the Czech Academy of Sciences, Prague, Czech Republic 3. School of Nano Convergence Technology, Hallym University, Chuncheon, Korea 4. Institute of Applied Physics, Military University of Technology, Warsaw, Poland 5. Institute of Physics, University of Silesia, Chorzów, Poland 6. Peter the Great Saint-Petersburg Polytechnic University, St.-Petersburg, Russia

Resume : Antiferroelectric perovskite crystals are technologically important materials with a complex picture of phase transitions. Among the parameters that affect strongly the stability of particular phases are temperature, pressure, and chemical doping. We present the results of our recent structural studies to indicate the similarities and differences between the effects of hydrostatic pressure and Sn4+ ion doping of lead hafnate, PbHfO3. The latter can be understood as chemical pressure since Sn4+ ions have slightly smaller ionic radii than Hf4+ ions. For this purpose, the solid solutions of Pb(Hf1-xSnx)O3 (0< x?0.3) were characterized using single-crystal X-ray diffraction, X-ray diffuse scattering, and Raman light scattering in the wide temperature range. The information on the structure of two intermediate phases, situated between low-temperature antiferroelectric A1 and high temperature paraelectric (PE) phases has been obtained. The lower-temperature intermediate A2 phase is characterized by incommensurate displacive modulations in the Pb sublattice, while the IM phase is of AFD (antiferrodistorsive) character mainly related to antiphase octahedral tilts. It was found that the resulting IM phase has a long-range order of oxygen octahedral rotations and Pb atomic displacements which are still correlated only on a short-range with some signatures of local modulation. Hence, an attempt has been made to define the symmetry of the IM phase. The candidate for IM-phase unit cell was the orthorhombic Imma defined by vectors ~aIM = (aPC;-aPC; 0), ~bIM = (aPC; aPC; 0) and ~cIM = (0; 0; 2aPC), where aPC is the pseudocubic lattice parameter. Oxygen octahedra are tilted in (a-a-c0) pattern around ~aIM. This cell corresponds to the average structure of the incommensurate phase of PHO, as determined crystallographically. Optical phonons and phase transitions in Pb(Hf1?xSnx)O3 single crystals were investigated by temperature-dependent Raman spectra. It was found that several soft modes control the phase transition between two antiferroelectric phases indicating its displacive character, whereas, in the paraelectric phase, both soft modes and Rayleigh scattering were observed. Finally, the complete phase diagram of Pb(Hf1-xSnx)O3 in temperature composition space is presented.

Authors : Magdalena Krupska-Klimczak, Irena Jankowska-Sumara, Dorota Sitko, Przemysław Gwizd
Affiliations : Institute of Physics, Pedagogical University of Cracow

Resume : The electrocaloric effect (ECE) of ferroelectrics is a coupling of electrical and thermal properties which results in an adiabatic temperature change dT in response to an externally applied electric field dE. It is is relatively new and a challenging research topic in the field of ferroelectric materials. This phenomenon has attracted large attention due to its potential use in environment-friendly solid-state cooling applications. Thus potential expectations of EC effect in cooling micro-devices are enlivened by searching for new more efficient materials. In this work, the electrocaloric effect was determined by the indirect method for the BaTiO3 (pure and doped with 1, 2, and 3% of Eu3+ ions) ceramics. The ECE was characterized via P–T curves under different electric fields. For all of the samples, the experiments have been carried out from room temperature through the phase transition region and in the paraelectric phase. The temperature dependences of polarization for different electric fields were deduced from the upper branches of the hysteresis loops whereas the values of electrocaloric temperature change (dT) were obtained using the Maxwell relations i.e. from the numerical differentiation of the polarisation versus temperature. The ECE obtained for pure BaTiO3 ceramics was found to be similar to that reported in the literature for fine-grained BaTiO3 ceramics. The ECE measured for the dopped samples has shown smaller positive ECE around the phase transition temperature. The values of ECE were generally comparable to those presented in the literature.

Authors : Md Redwanul Islam, Georg Schönweger, Niklas Wolff, Simon Fichtner, Lorenz Kienle
Affiliations : Md Redwanul Islam; Niklas Wolff; Simon Fichtner; Lorenz Kienle Synthesis and Real Structure, Department of Materials Science, Kiel University, Kaiserstraße 2, Kiel, Germany. Georg Schönweger Institute of Electrical and Information Engineering, Kiel University, Kaiserstr. 2, 24143 Kiel, Germany. Simon Fichtner Fraunhofer Institute for Silicon Technology (ISIT), Fraunhoferstr. 1, D-25524 Itzehoe, Germany.

Resume : AlScN as a ferroelectric (FE) - first introduced in 2019, is a new class of nitride FE with wurtzite-type (w) crystal structure. Since then, the material gained significant interest in the field of FE based micro and nano-electronics due its “easy-deposition” processes compared to commercially available perovskite oxide ferroelectrics (e.g., PZT, BaTiO3) [1, 2]. The material also has a very high Curie temperature and proved compatible for GaN-technology [3, 4]. However, the switching characteristics of AlxSc1-xN FE capacitors on n-GaN have been affected by depletion at the AlxSc1-xN-GaN interface [5]. This leads to broadening of the switching regime - increasing leakage during switching. In this study, we have introduced a modified system with 12 nm ultra-thin metal Pt electrode grown in between the n-GaN and Al0.72Sc0.28N. With this, the depletion at the interface was significantly nullified. High resolution X-ray diffraction on these films revealed that Pt grows epitaxially on n-GaN, therefore preserves the epitaxial growth of w-AlScN at a certain degree. Furthermore, the FE layer thickness can be scaled down to at least 20 nm. Overall, our study depicts a new w-AlScN/Pt/n-GaN system with significantly reduced depletion during FE switching as well as depicts a move towards AlxSc1-xN based 2D epitaxial metal-ferroelectric-metal capacitors. References: [1] Simon Fichtner, Niklas Wolff et. al., Journal of Applied Physics 125, 114103 (2019) [2] Piazza, G., Felmetsger, V., Muralt et. al., MRS Bulletin 37, 1051–1061 (2012). [3] Md. Redwanul Islam, Niklas Wolff et. al., Appl. Phys. Lett. 118, 232905 (2021) [4] Christian Manz et. al., 2021 Semicond. Sci. Technol. 36 034003 [5] Schönweger, G., Petraru, A., et. al., Adv. Funct. Mater. 2022, 32, 2109632.

Authors : D. Z. Dimitrov1,2, J.-Y. Juang3, V. Marinova2, M.M. Gospodinov1
Affiliations : 1. Institute of Solid State Physics, Bulgarian Academy of Sciences, Sofia, Bulgaria; 2. Institute of Optical Materials and Technologies, Bulgarian Academy of Sciences, 3. Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu, Taiwan

Resume : Single crystals of CaMn2O4 ( Marokite) were grown using the high-temperature solution growth method. CaCl2 was used as flux and the ratio between the starting products and the flux (CaO + 2MnO2):CaCl2 was 1:20. Crystal characterization was determined by powder X-ray diffraction. CaMn2O4 crystallizes in the orthorhombic Pbcm space group with unit cell parameters a =3.1478(2)Å, b =9.9750(6)Å, and c = 9.6647(7)Å. The structure is three-dimensional. Ca2+ is bonded in 8-coordinate geometry to eight O2- atoms. Temperature and pressure dependences of the magnetic and dielectric properties (capacitance, dielectric constants, polarization, magnetization, TN, pyrocurrent) were measured in order to assess the quality of the single crystals. For various applications it is necessary to prepare single crystals with high-quality. CaMn2O4 is one of potential cathode materials [1] for the new calcium-ion based battery technology. Acknowledgement: Financial support by the Bulgarian National Scientific Fund under the Project КП-06-КОСТ/13 is gratefully acknowledged. Reference: [1] M. Elena Arroyo-de Dompablo et al., Chem. Mater. 2016, 28, 19, 6886–6893

Authors : E. Palladino [1], S. Pal [1], M. A. De h-Ora [2], J. L. MacManus-Driscoll [2], J. Briscoe [1]
Affiliations : [1] School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, London E1 4NS, UK [2] Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB3 0FS UK

Resume : Ferroelectric materials are known to possess interesting physical and electrical properties that can be exploited in multiple applications in random access memories (FeRAM), energy harvesting, transducers, sensors, and biomedicine. Their non-centrosymmetric unit cell gives rise to a spontaneous switchable polarization under an applied electric field. Furthermore, these materials can develop photovoltages much higher than their bandgap and do not require a junction to drive exciton dissociation, a phenomenon known as the bulk photovoltaic effect (BPV)1, which could potentially overcome the Shockley-Queisser (S-Q) limit for single junction devices. However, the high photovoltage requires low photoconductivity which together with the intrinsic wide band gaps of most ferroelectrics limit their efficiency below 1%2. A viable route to overcome these limitations is to couple the ferroelectric phase with a photoabsorbing phase in a nanocomposite device in order to harvest a higher portion of the solar spectrum, reduce series resistance and stabilize the ferroelectric phase via strain engineering, 3,4. In this work, we report the preparation of BaTiO3 thin films via sol-gel method and pulsed laser deposition (PLD), with controlled degrees of porosity via additive concentration and deposition parameter control, respectively. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to analyse and compare the morphologies of the films. Accurate maps of ferroelectric domains and switching parameters were obtained via piezoresponse force microscopy (PFM) and switching spectroscopy (SS-PFM) techniques. Here we demonstrate that epitaxially grown thin films offer a higher degree of control of the ferroelectric phase and allow us to accurately tailor the film parameters, while the polycrystalline films at low porosity levels remain a valid alternative for quick and low-cost processing. References 1. Lopez-Varo, P. et al. Physical aspects of ferroelectric semiconductors for photovoltaic solar energy conversion. Phys. Rep. 653, 1–40 (2016). 2. Wu, L., Podpirka, A., Spanier, J. E. & Davies, P. K. Ferroelectric, Optical, and Photovoltaic Properties of Morphotropic Phase Boundary Compositions in the PbTiO3-BiFeO3-Bi(Ni1/2Ti1/2)O3 System. Chem. Mater. 31, 4184–4194 (2019). 3. Choi, K. J. et al. Enhancement of ferroelectricity in strained BaTiO3 thin films. Science (80-. ). 306, 1005–1009 (2004). 4. Harrington, S. A. et al. Thick lead-free ferroelectric films with high Curie temperatures through nanocomposite-induced strain. Nat. Nanotechnol. 6, 491–495 (2011).

Authors : Georgy Gordeev, Mads Weber, Stephanie Reich, Mael Guennou
Affiliations : Department of Physics and Materials Science, University of Luxembourg, 41 Rue du Brill, L-4422, Belvaux, Luxembourg; Institut des Molécules et Matériaux du Mans, UMR 6283 CNRS, Le Mans Université, 72085, Le Mans, France; Department of Physics, Freie Universität Berlin, Berlin 14195, Germany; Department of Physics and Materials Science, University of Luxembourg, 41 Rue du Brill, L-4422, Belvaux, Luxembourg

Resume : Rare-earth orthoferrites RFe03 is a family of materials hosting a range of exotic physical properties and structural phases. However, the underlying electron band structures of such structures is not well understood. The theoretical calculations are complicated by the manifold interactions between magnetic-vibrational and electronic degrees of freedom. We investigate optical transitions to gain insights into the structure of electronic states near the Fermi level. Together with the classical band to band transitions one could find defect-induced, charge-transfer excitations as well as the transitions within rare-earth electrons. We first focus on the SmFeO3 single crystal and cross-correlate pure optical techniques, such as reflectivity and ellipsometry with resonance Raman spectroscopy, which additionally involves phonon interactions. The Raman scattering efficiency is anisotropic and depends on symmetries of the scattered phonons. By comparing the resonant behavior of the different modes, we can study intrinsic magneto-electronic and magneto-vibrational interactions.

Authors : Adil Alshoaibia , Mohammed Benali Kanouna, , Bakhtiar Ul Haqb , Salem AlFaifyb , Souraya Goumri-Said
Affiliations : Department of Physics, College of Science, King Faisal University, P.O. Box 400, Al-Ahsa 31982, Saudi Arabi

Resume : Oxide perovskites doped with rare-earth have shown change in optoelectronic properties with high dielectric constants. Herein, the structural, electronic, and optical characteristics of BaTiO3 doped with ytterbium at the Ba and Ti sites were studied by employing the first-principles density functional calculations. The Tran-Blaha modified Becke-Johnson (TB-mBJ) potential and GGA + U approaches have been used for determining the optoelectronic properties. We probed the impact of the ytterbium incorporation at the Ti and Ba sites into BaTiO3 by tuning of the structural geometry and electronic structure behavior and dielectric constants. A detailed analysis, of structural properties, reveals that lattice parameters of ytterbium doping shift slightly regarding those of pristine BaTiO3. The BaeO and TieO bond lengths were reduced due to the crystalline structure lattice distortion. The band structures demonstrate that ytterbium doping has induced various changes in the electronic nature of BaTiO3 by creating a magnetism. For both Ba and Ti sites, ytterbium doping has strongly increased the BaTiO3 dielectric constants.

Authors : Adil Alshoaibi, Mohammed Benali Kanoun, Bakhtiar Ul Haq, Salem AlFaify, and Souraya Goumri-Said
Affiliations : Department of Physics, College of Science, King Faisal University, Al-Ahsa 31982, Saudi Arabia; Email:

Resume : We reported a systematic study of the effects of Y doping BaTiO3 at Ba and Ti sites. We assessed the structural, electronic, and optical properties by employing first-principles calculations within the Tran−Blaha-modified Becke−Johnson (TB−mBJ) potential and generalized gradient approximation + U approaches. We calculated the lattice constants and bond lengths for pure and Y-doped BaTiO3. We explored the consequences of electronic structure and optical property modification because of Y doping in BaTiO3. Indeed, Y doping has led to various modifications in the electronic structures of BaTiO3 by inducing a shift of the conduction band through lower energies for the Ba site and higher energies for the Ti site. It was found that Y doping, either at Ba or at Ti sites, strongly enhanced the BaTiO3 dielectric constant properties. The transformation in bonding was explored via the charge density contours and Born effective charges. We used the state of art of polarization theory based on finite difference and Berry-phase approaches to investigate piezoelectricity. Y doping has increased the dielectric constants but canceled the piezoelectricity as they changed to metallic nature. We could look into the future for potential doping, preserving the semiconductor nature of BaTiO3 and increasing the permittivity with large dielectric loss.

Authors : D. Havryliuk, I. Gruszka, M. Zubko, M.Wojtyniak and J. Piecha,
Affiliations : A. Chełkowski Institute of Physics, University of Silesia, ul. 75 Pułku Piechoty 1,41-500 Chorzów, Poland; Institute of Materials Engineering, University of Silesia in Katowice, ul. 75 Pułku Piechoty 1a, Chorzów, 41-500, Poland; Institute of Physics—Center for Science and Education, Silesian University of Technology, Krasińskiego 8, 40-019 Katowice, Poland

Resume : Lead hafnate PbHfO3 is an antiferroelectric perovskite oxide known in the form of ceramics and crystals. Different doping is used to improve its properties as the material for electric energy storage in high-power applications [1,2]. This work presents the first results of synthesizing lead hafnate crystals doped with lanthanum. The Pb100-xLaxHfO3 crystals were obtained by crystallization from a molten solution, and their structure was verified by the X-ray diffraction method at room temperature. The atomic composition of the elements was determined by X-ray fluorescence spectroscopy. The crystals were investigated using dielectric spectroscopy on cooling and heating cycles and revealed a similar sequence of transitions as in PbHfO3. Compared to pure lead hafnate, the permittivity of doped crystals diminished, and phase transition points slightly moved toward lower temperatures. 1. Peng-Zu Ge et al.; Ultrahigh energy storage density and superior discharge power density in a novel antiferroelectric lead hafnate, Materials Today Physics 24, 2022, 100681 2. Dongxu Lia et al., Progress and perspectives in dielectric energy storage ceramics, Journal of Advanced Ceramics 10(4), 2021, 675–703

Authors : Marek Paściak
Affiliations : FZU - Institute of Physics of the Czech Academy of Sciences

Resume : The antiferroelectric phase transition in PbZrO3 (PZO) with eightfold unit cell multiplication is shaped by a coupling between polar and octahedra tilting distortion modes. The exact form of this coupling has been the matter of intense debate in recent years, e.g. [1-3]. It is nonetheless clear that the cooperation of the modes makes the potential energy landscape rather complicated with various states/symmetries being very close in energy [2] hinting at the role of structural disorder [3]. The multi-state nature exhibits itself in the intermediate (IM) phase that appears upon a small substitution of Zr with Ti [4]. Therein a mixture of incommensurate and monoclinic phases has been observed. The former dominates the intermediate region in another substituted system – Pb(Zr,Sn)O3 [5]. On the top of that there a diffraction evidence of the high abundance of anti-phase boundaries in both pure and solid-solution systems in the IM and antiferroelectric phases. It is clear that the substitutions introduce intrinsic disorder but at the same time they give a chance for decoupling of distortion modes in the intermediate phases [4,5]. In this work we use first-principle as well as shell-model calculations to address this complexity of PbZrO3-based materials and the interaction of polarization and octahedra tilting. We discuss the low-energy structural variants and their stability at various conditions. Furthermore, the attention is paid to intermediate monoclinic phases and the internal structure of anti-phase boundaries. We acknowledge the support from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 964931 (TSAR). [1] J. Hlinka et al., Phys. Rev. Lett. 112, 197601 (2014). [2] J. Íñiguez, M. Stengel, S. Prosandeev, and L. Bellaiche, Phys. Rev. B 90, 220103(R) (2014). [3] B. Xu, O. Hellman, and L. Bellaiche, Phys. Rev. B 100, 020102(R) (2019). [4] Z. An et al., Phys. Rev. B 103, 054113 (2021). [5] I. Jankowska-Sumara et al., APL Materials 9, 021101 (2021).

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Session 9:00 - 10:30 : Chair - Sabine Körbel
Authors : Mael Guennou
Affiliations : University of Luxembourg

Resume : The most characteristic signature of antiferroelectric materials is their electric-field induced phase transition to a polar phase and the associated response of polarization as a function of field P(E). In practice, a very large body of published work revolve around a few end compounds with the perovskite structure both lead-based (PbZrO3 and PbHfO3) and lead-free (AgNbO3 and NaNbO3). The antiferroelectric character of these end compounds are basically known for decades even though they may not be understood in details because of the complexity of the microscopic mechanisms involved. In principle, it would be desirable to identify other families of compounds with different crystal structures in order to enrich this portofolio of potential antiferroelectrics. This is desirable both from a theoretical perspective, in order to better appreciate the variety of microscopic mechanisms responsible for antiferroelectricity, but also from application perspectives for a broader choice of end compounds. The search for new antiferroelectric materials however is impeded by a number of difficulties, starting with the somehow ambiguous definition of the notion itself. This includes also difficulties in identifying characteristic symmetry criterion or experimental signatures that could be used to screen efficiently large families of crystals. In this talk I will describe our theoretical and experimental approaches to this problem and our attempts to identify such signatures. This has led us to identify a unique example of a displacive antiferroelectric transition and explore the potential for antiferroelectricy in scheelites.

Authors : Philippe Ghosez
Affiliations : Theoretical Materials Physics, CESAM, University of Liege

Resume : Calcium titanate is the original compound to which the name of perovskite was attributed. Although showing a ferroelectric instability in its aristotype cubic reference structure, it is not ferroelectric. Instead, like many other oxide perovskites, it adopts an orthorhombic Pnma ground state, which emerges from the condensation of oxygen-octahedra rotation and tilts through a phase transition sequence that remains partly controversial. It was sometimes suggested that calcium titanate could be an incipient ferroelectric like strontium titanate. It can also be questioned why it is not antiferroelectric like lead zirconate. Here, using a second-principles approach, we will reinvestigate the phase transition sequence of calcium titanate with temperatures. We will provide a possible explanation to its apparent incipient ferroelectric character, sometimes observed experimentally. We will also question why it is not antiferroelectric and try to rationalize what makes it so different from lead zirconate showing however a very similar tolerance factor. Work done in collaboration with M.M. Schmitt, L. Bastogne, H. Zhang and C. H. Chao and supported by F.R.S.-FNRS Belgium (PDR project PROMOSPAN) and by the European Union’s Horizon 2020 research and innovation program under grant agreement N° 766726 (TSAR).

Authors : Hugo Aramberri (1,2), Jorge Íñiguez (1,2,3)
Affiliations : (1) Materials Research and Technology Department, Luxembourg Institute of Science and Technology,
 5 avenue des Hauts-Fourneaux, L-4362 Esch/Alzette, Luxembourg
 (2) Inter-institutional Research Group–LIST on Ferroic Materials, 41 rue du Brill, L-4422 Belvaux, Luxembourg (3) Department of Physics and Materials Science, University of Luxembourg, 41 Rue du Brill, L-4422 Belvaux, Luxembourg

Resume : Antiferroelectrics are among the most promising materials for applications as high energy storage capacitors. Yet, the number of known antiferroelectrics is relatively small, which hinders their usage. Moreover, the optimization of their performance for energy storage is still somewhat limited, partly due to our incomplete understanding of the physical mechanisms yielding antiferroelectric order. In this talk we present our latest theoretical works on antiferroelectrics. Lead zirconate is considered the prototypical antiferroelectric perovskite. However, several experimental and theoretical works hint at a partially polar behaviour in this compound, indicating that the polarization may not be completely compensated. We propose a new structure for this material with uncompensated dipoles following a ferrielectric up-up-down pattern. First-principles calculations reveal this state to be more stable than the commonly accepted antiferroelectric state at low temperatures, possibly up to room temperature, suggesting that PbZrO3 may not be antiferroelectric at ambient conditions. We discuss the implications of this discovery, how it can be reconciled with the experimental observations and how the predicted ferrielectric phase could be obtained in practice. We also explore the possibility of designing artificial antiferroelectrics using ferroelectric/paraelectric superlattices. When surrounding a ferroelectric by dielectric layers, a competition between the polar distortion and the depolarizing field arises, often resulting in a rupture of the ferroelectric into domains of alternating polarization. Such system can be considered antipolar and can switch into a polar state under an electric field. We study the antiferroelectric-like response of PbTiO3/SrTiO3 superlattices by means of high-throughput second-principles calculations. By optimising their energy density and efficiency, we show that these systems are competitive with state-of-the-art antiferroelectrics for energy storage and offer a platform for further systematic optimization.

10:30 Coffee break    
Session 11:00 - 12:30 : Chair - Mael Guennou
Authors : Mao-Hua Zhang (1), Changhao Zhao (1), Lovro Fulanović (1), Hui Ding (1), Niloofar Hadaeghi (1), Sonja Egert (2), Hongbin Zhang (1), Pedro B. Groszewicz (2,3), Jurij Koruza (4)*
Affiliations : 1. Department of Materials and Earth Sciences, Technical University of Darmstadt, Germany 2. Physical Chemistry of Condensed Matter, Technical University of Darmstadt, Germany. 3. Department of Radiation Science and Technology, Delft University of Technology, Netherlands. 4. Institute for Chemistry and Technology of Materials, Graz University of Technology, Austria. * Presenting author:

Resume : Antiferroelectrics exhibit unique electrical properties, which originate from the complex antiparallel arrangement of the spontaneous polarization. Typically, a ferroelectric phase with a comparable free energy to the antiferroelectric phase exists and it can be induced by different external stimuli (electric field, temperature, stress). Compositions in which this transition is reversible exhibit characteristic double polarization loops and could be used for high-energy storage capacitors or electrocaloric cooling [1,2]. NaNbO3 is a prototypical lead-free antiferroelectric material that serves as the basis for the development of new compositions. However, the field-induced transition in pure NaNbO3 is irreversible and thus the material retains the ferroelectric order after field removal [3]. To understand this behavior, we first investigated the nature of this phase transition using electromechanical and structural characterization. The macroscopic increase in polarization/strain and inducement of piezoelectricity were accompanied by microscopic disappearance of the translational domain structure and changes of the local Na environment. Moreover, in situ high-energy X-ray diffraction measurements revealed that the transition is subdivided into three stages [4]. In order to obtain a reversible field-induced phase transition, a series of (1-x)NaNbO3-xSrSnO3 (x=0-0.06 mol.%) compositions were designed under the guidance of first-principles calculations and processed using the solid-state reaction route [5]. Although the global structure was maintained, 23Na solid-state nuclear magnetic resonance study showed an increase in the overall disorder and a less distorted local environment of Na in the NaO12 cuboctahedra. Double polarization hysteresis loop indicating the reversible nature of the phase transition were observed in the SrSnO3-modified samples, with a 14-times higher energy storage density (1.7 J/cm3) as compared to pure NaNbO3 and an efficiency of 33%. [1] Hao et al., Prog. Mater. Sci. 63, 1 (2014) [2] Novak et al., Phys. Rev. B 97, 094113 (2018) [3] Zhang et al., Acta Mater. 200, 127 (2020) [4] Zhang et al., Appl. Phys. Lett. 118, 132903 (2021) [5] Zhang et al., Chem. Mater. 33, 266 (2021)

Authors : Lukas Riemer, Milica Vasiljevic, Paul Muralt, Dae-Sung Park, Dragan Damjanovic
Affiliations : Institute of Materials, Ecole polytechnique fédérale de Lausanne, Lausanne, Switzerland

Resume : Recent studies indicate that spontaneous symmetry breaking may be common in a wide range of dielectric materials, even if the physical origins of the phenomenon are different. By symmetry breaking we here consider appearance of a macroscopic piezoelectric effect or macroscopic polarization in a nominally centrosymmetric material. In this talk we shall discuss such symmetry breaking in canonical relaxor, Pb(Mg1/3Nb2/3)O3 (PMN), paraelectric phase of prototypic ferroelectric BaTiO3 and (Ba,Sr)TiO3, cubic Gd-doped CeO2 with fluorite structure and organometallic halide perovskites. To study macroscopic asymmetry we apply different techniques, including pyroelectric measurements, thermally stimulated currents, measurements of nonlinear polarization and strain, mechanical poling and illumination. These techniques are complementary and together reveal complexity of this emerging phenomenon. Our results suggest that there are at least two competing mechanisms contributing to polarization dynamics in PMN. The mechanism dominant at high fields is consistent with the dynamic switching of polar entities while the weak-field mechanism leads to a response resembling the weak-field motion of domain walls in hard ferroelectrics. It is possible to show that the transition between these two dynamic regions happens at alternating fields which are comparable in amplitude to the strength of the static field needed to switch the direction of spontaneous macroscopic polarization. Interestingly, the PMN single crystals could be poled by mechanical force. Our results question the ergodic nature of relaxor PMN below the Burns temperature. Electric-field induced symmetry breaking in Gd-doped CeO2 leads to huge values of the apparent piezoelectric d coefficient at low frequencies of the probing alternating field. The atomistic mechanism of symmetry breaking in this material is related to a high mobility of ionic defects (oxygen vacancies) and the resulting strain is a combination of redistribution of oxygen vacancies, chemical expansion effects and electric field-induced phase transition. In methylammonium (MA) lead halide single crystals with cubic structure (MAPbX3, X=Br, Cl) we revealed the appearance of symmetry breaking which is strongly dependent on defect structure and history of the samples. Some resemblance exists between electrostrictive and piezoelectric behavior in Gd-doped CeO2 and these organometallic perovskites, underlying ionic origin of the electro-mechanical coupling. An interesting aspect of MAPbX3 is that the generated piezoelectric strain depends on UV illumination. We discuss whether the macroscopic symmetry breaking is essentially related to the presence and mobility of defects or the symmetry can be broken in “perfect” crystals, as suggested by recent first-principles studies.

Authors : W.Schranz, A. Tröster, I. Rychetsky
Affiliations : University of Vienna, Faculty of Physics, Physics of Functional Materials, Boltzmanngasse 5, A-1090 Wien, Austria; Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 18221 Prague 8, Czech Republic

Resume : Domain walls have been recognized as exciting objects, due to their ability to carry functional properties, that are absent in the surrounding bulk domains [1, 2]. In the present talk we discuss the symmetry and properties of domain walls of various perovskites (e.g. SrTiO3, PbZrO3, PbTiO3) using a recently developed method of combining layer group analysis [3] with order parameter symmetry and Landau-Ginzburg theory [4, 5] and compare the results with some experimentally determined properties of the corresponding materials [6,7] and with recent results from computer simulations [8]. [1] G. Nataf, M. Guennou, J. Gregg, D. Meier, J. Hlinka, E. Salje, and J. Kreisel, Nature Reviews Physics 2, 634 (2020). [2] P. Sharma, Q. Zhang, D. Sando, C. H. Lei, Y. Liu, J. Li, V. Nagarajan, and J. Seidel, Science advances 3, e1700512 (2017). [3] V. Janovec, Ferroelectrics 12, 43 (1976). [4] W. Schranz, I. Rychetsky and J. Hlinka, Phys. Rev. B 100, 184105/1-14 (2019). [5] W. Schranz, C. Schuster, A. Tröster and I. Rychetsky, Phys. Rev. B 102, 184101/1-12 (2020). [6] W. Schranz, A. Tröster and I. Rychetsky, Journal of Alloys and Compounds 890, 161775 (2022). [7] I. Rychetsky, W. Schranz and A. Tröster, Phys. Rev. B 104, 224107 (2021). [8] A. Tröster, C. Verdi, C. Dellago, I. Rychetsky, G. Kresse and W. Schranz, Hard Antiphase Domain Boundaries in Strontium Titanate unravelled using Machine-Learned Force Fields, submitted to Phys. Rev. Lett.

12:30 Lunch    
Session 14:00 - 15:30 : Chair - Jurij Koruza
Authors : B. Dkhil* *on behalf of many co-authors
Affiliations : Université Paris-Saclay, CentraleSupélec, CNRS-UMR8580, Laboratoire Structures, Propriétés et Modélisation des Solides, 91190 Gif-sur-Yvette, France

Resume : An artificial neural network is basically an ensemble of neurons connected by weighted synaptic connections allowing superior computing performances over classical von Neumann-based systems in processing cognitive and data intensive tasks, such as real-time image recognition, data classification or natural language processing, to cite a few. Typically, the information represented by a weight for each synapse is transmitted from the pre-synaptic neuron to the post-synaptic neuron. The network is then trained by updating its synaptic weights to perform a specific task. In the race for efficient materials to emulate neuronal and synaptic functions, classical ferroelectrics, both oxides and PVDF-based polymers have been considered as good candidate materials. Here, we take advantage of the polar instabilities and the flat energy landscape characteristic of relaxors to exploit this special class of ferroelectrics for mimicking neuromorphic elements. We show that field-induced transitions are useful for tuning the capacitance and polar responses along multiple states and in a non-volatile manner to reproduce mem-ristor/capacitor behaviors. We use such component to emulate some fundamental learning rules including long-term memory or spike-timing-dependent-plasticity. Using modelling, we also show that ultrafast THz electric field excitations enable both neuronic and synaptic behaviors, via the creation of out-of-equilibrium hidden states of polarization, resulting from the ultrafast response of polar nanoregions. These findings may open a new field of research dedicated to employ relaxors for the design of neuromorphic architecture and computing.

Authors : Oktay Aktas
Affiliations : State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, China

Resume : Compound phases often display properties that are symmetry forbidden by their nominal, average crystallographic symmetry, even if extrinsic reasons (defects, strain, or imperfections) are not apparent. An example of such disallowed property is piezoelectricity in nominally centrosymmetric phases and shows great potential to be exploited in device applications. In this work, Resonant Piezoelectric Spectroscopy (RPS) was used as the method of choice and the piezoelectric effect was quantified in unpoled ferroelectrics and a large number of nominally centrosymmetric materials, including paraelectrics, relaxors, ferroelastics, and isotropic materials with low defect concentrations. Values range from ~1 pm/V to 10-5 pm/V. The former is comparable to that of piezoelectric quartz whereas the latter is 3 orders of magnitude below the detection limit of conventional piezoelectric measurements. Polar nanostructures, such as precursors of ferroelectrics in the paraelectric phase, polar nano regions in relaxors above the freezing temperature, twin walls in ferroelastics, and coherent dipole complexes at cryogenic temperatures, are yet to be experimentally confirmed as the cause of symmetry breaking; however, they make a dominant contribution to piezoelectricity, with the piezoelectric effect significantly enhanced below a characteristic temperature. This temperature appears to be analogous to the coherence temperature T* which is commonly used for relaxors and is associated with the development of quasi-static regions and nanotwinning within PNR’s. Considering an obvious role of polar nanostructures in the enhanced piezoelectricity below T* and recent observations of static nano clusters in the paraelectric phase of BaTiO3, the influence of DC electric fields on the paraelectric phase of ferroelectric PbSc0.5Ta0.5O3 (PST) (with 65% B-site cation order) was also investigated. The application of the DC electric field results in remnant piezoelectricity, which disappears after the sample is heated above the coherence temperature T*~450 K. In a temperature region between the ferroelectric transition temperature Tc = 295 K and 355 K, even electric fields below the coercive field of PST lead to strong remnant piezoelectricity, whereas above ~355 K remnant piezoelectricity is drastically reduced. These results are attributed to poling of ferroelectric precursors, which manifest themselves as macroscopic switchable piezoelectricity, and suggest that increased coherency of precursors leads to a microscopic transition at 355 K, presumably to form a stable tweed structure.

Authors : Andreas Klein
Affiliations : Technical University of Darmstadt, Institute of Materials Science, Electronic Structure of Materials, Otto-Berndt-Straße 3, 64287 Darmstadt, Germany

Resume : The stability of piezoelectric/metal interfaces is particularly important for multilayer ceramic capacitors and decides about the choice of suitable electrode materials. Noble metal interfaces such as Pt or Ag-Pd are suitable for sintering of capacitors in air but are important cost factors. Non-noble metal electrode materials such as Cu or Ni will oxidize during sintering in air and thereby loose their conductivity, hence sintering in reducing conditions is required. This may lead to a decomposition of piezoelectric. In this contribution, it will be shown the instability of the piezoelectric is caused by an electrochemical instability, induced by a too high Fermi energy of electrodes with low work function. Photoelectron spectroscopy is used to analyze the evolution of the Schottky barrier heights and chemical composition at interfaces between various piezoelectrics and Sn-doped In2O3 model electrodes (ITO). The Fermi energy in the 3 nm thick ITO electrode is continuously raised during XPS measurement either by heating in vacuum or by cathodic polarization of the ITO electrode at elevated temperature. Thereby we observe a limitation of the Fermi energy at the interface, which is accompanied either by the observation of metallic Pb (PZT and related compounds), metallic Bi (NBT-BT), or by diffusion of Na or K through the ITO electrode (KNN). Together with the previously observed electrochemical reduction of BiFeO3 [1], it is concluded that the stability of piezoelectric interfaces is fundamentally determined by the Schottky barrier at the contact. [1] N.S. Bein, AK, et al, J. Phys. Chem. Lett. 10 (2019), 7071.

15:30 Coffee break    
Session 16:00 - 17:30 : Chair: Sara Gonzalez
Authors : G. De Luca, S. Ganguly, J. Padilla, J. M. Caicedo, J. Santiso, G. Catalan
Affiliations : Catalan Institute of Nanoscience and Nanotechnology (ICN2)

Resume : The discovery of ferroelectricity and antiferroelectricity in ultrathin films of the fluorite system Hf1-xZrxO2 (HZO) triggered a lot of attention because of its potential integration with current semiconductor technology that would facilitate the development of low-energy consuming devices [1]. Despite polycrystalline films are the main ingredient for potential applications, epitaxial single-phase highly-crystalline thin films would enable a deeper understanding and control of the ferroic properties of HZO. Most of the work in this area has so far been focused on integrating fluorite HZO on the well-known perovskite oxide architecture [2]. Unfortunately, in these kind of heterostructures the HZO give rise to texturing and coexistence of different phases that can inhibit a clear understanding of the structure-property relationship [3]. To mitigate this phase coexistence, we use a different epitaxial design and directly grow the HZO on buffered and pristine YSZ fluorite substrates. To further minimize any disorder related with Hafnium-Zirconium mutual doping, we focus on the x = 1 composition (ZrO2). Our films grow epitaxial and with a single phase, with different growth parameters (thickness, temperature, buffer layer) affecting the resulting ZrO2 fluorite polymorph. Direct integration of HZO ceramics on buffered fluorite substrates has the potential to become a new platform for understanding how epitaxial strain, confinement and different interfaces can affect the properties of HZO and related systems. [1] J. Müller et al., “Ferroelectricity in simple binary ZrO 2 and HfO 2,” Nano Lett., vol. 12, no. 8, pp. 4318–4323, 2012. [2] I. Fina and F. Sánchez, “Epitaxial Ferroelectric HfO 2 Films: Growth, Properties, and Devices,” ACS Appl. Electron. Mater., p. acsaelm.1c00110, Apr. 2021. [3] T. Song et al., “Positive Effect of Parasitic Monoclinic Phase of Hf0.5Zr0.5O2 on Ferroelectric Endurance,” Adv. Electron. Mater., vol. 2100420, 2021.

Authors : Alfredo Blázquez Martínez,1,2,3 Patrick Grysan,1 Stéphanie Girod,1 Veronika Kovacova,1,3 Sebastjan Glinsek,1,3 Pranab Biswas,2,3 Mael Guennou,2,3 Torsten Granzow1,3
Affiliations : 1Luxembourg Institute of Science and Technology, Materials Research and Technology Department, 41 rue du Brill, L-4422 Belvaux, Luxembourg 2University of Luxembourg, 41 rue du Brill, L-4422 Belvaux, Luxembourg 3Inter-institutional Research Group–LIST on Ferroic Materials, 41 rue du Brill, Belvaux L-4422, Luxembourg

Resume : Bismuth ferrite (BiFeO3, BFO) is one of the few multiferroic materials with both, ferroelectric and antiferromagnetic ordering at room temperature. The bulk photovoltaic (BPV) properties of BFO were first reported in 2009. Due to the high remanent polarization (~100 μC/cm2) and its “narrow” bandgap compared to other ferroelectrics, BFO has been the focal point in most research on ferroelectric photovoltaics. Besides, the high Curie temperature of BFO (TC = 1013 K) being compatible with high-temperature applications, its high birefringence and its lead-free nature make BFO a candidate for electro-optic (EO) applications. The understanding of both the BPV and EO response of BFO is essential for the study of the photorefractive properties in BFO that are generally suppressed by its high conductivity. Here, we present highly (100)-textured polycrystalline BFO thin films fabricated by solution processing. Low leakage films with epitaxial-like ferroelectric properties were obtained by co-doping with manganese and titanium and by precise control of the microstructure.[1] The photovoltaic properties were measured using interdigitated electrodes. We show that the main light-induced charge transport mechanism is the BPV effect, the first such demonstration for a solution-deposited polycrystalline film.[2] The EO properties were quantified by a modified Teng-Man setup in transmission geometry, obtaining EO coefficients (reff) up to 3 pm/V, reaching values about 25% of those reported for epitaxial films.[3] The results on the BPV effect and the EO properties are used to assess the potential of using solution-processed films for photorefractive applications. [1] A. Blázquez Martínez, N. Godard, N. Aruchamy, C. Milesi-Brault, O. Condurache, A. Bencan, S. Glinsek, T. Granzow, J. Eur. Ceram. Soc. 41 (2021) 6449–6455. [2] A. Blázquez Martínez, P. Grysan, S. Girod, S. Glinsek, T. Granzow, Scr. Mater. 211 (2022) 114498. [3] D. Sando, P. Hermet, J. Allibe, J. Bourderionnet, S. Fusil, C. Carrétéro, E. Jacquet, J.-C. Mage, D. Dolfi, A. Barthélémy, P. Ghosez, M. Bibes, Phys. Rev. B 89 (2014) 195106.

Authors : Hamideh Hassani, Bart Partoens, Eric Bousquet, and Philippe Ghosez
Affiliations : Theoretical Materials Physics, Q-MAT, CESAM, University of Liege, Liege, Belgium; Department of Physics, University of Antwerp, Antwerp, Belgium

Resume : Polarons are quasiparticles that form in a wide variety of materials as a result of electron?phonon coupling, and they typically have significant effects on materials properties. Although the concept is known since about 75 years, the origin of polarons is not yet fully elucidated. To date the most popular explanation relies on Fröhlich's theory: an electron placed in a crystal lattice will induce local polar screening achieved from the activation of a polar phonon mode and resulting in the formation of a polaron. WO3 is a well-known prototypical system for studying polarons since its polaronic nature is expected to be at the origin of its remarkable electrical and chromic properties. Here, using first-principles density functional calculations, we successfully predict the formation of medium size polarons in WO3. Amazingly, our calculations reveal however that, when an extra electron is added into WO3, it will dominantly activate non-polar rather than polar modes. This observation implies that, in addition to conventional Fröhlich's view, there should be another mechanism to stabilize the charge. Developing a simple model, we unveil and rationalize how this is intimately related to changes of hybridization between W 5d and O 2p orbitals. Our findings might be relevant to the whole family of ABO3 perovskites, to which WO3 is closely related.

Authors : Jan Petzelt, Viktor Bovtun, Dmitry Nuzhnyy, Martin Kempa, Maxim Savinov, Marek Paściak, Stanislav Kamba; Giovanna Canu* and Vincenzo Buscaglia*
Affiliations : Department of Dielectrics, FZU - Institute of Physics of the Czech Academy of Sciences, Prague, Czech Republic *Institute of Condensed Matter Chemistry and Technologies for Energy, CNR-ICMATE, Genoa, Italy

Resume : Broadband dielectric spectra (from Hz up to THz and infrared frequencies) of the xBaZrO3–(1-x)BaTiO3 (BZT) ceramic solid solutions will be presented. We studied the BZT system in a broad (almost complete) concentration range and in a broad temperature range from 10 to 700 K. BZT is a model lead-free system which, depending on the concentration x, behaves as incipient, relaxor, diffuse or classical ferroelectric material. The behaviour is compared to that of pure BaTiO3 and BaZrO3 end members. Based on the results of the broadband fits of the spectra, we will discuss different processes and their origins that play role in the dynamics, such as (soft) phonons and relaxations. The spectra are characterized by an overdamped central mode in the microwave range which weakens on cooling. Except for BaTiO3, the soft mode and central mode do not soften appreciably and do not contribute substantially to the low-frequency permittivity maximum. The most important dielectric contribution is brought by Cole-Cole relaxation assigned to the hopping of Ti ions in the BaTiO3 clusters, which obeys the Arrhenius law. We acknowledge the support from the grant of the Czech Science Foundation (Project LA 20-20326L).

Authors : C. Saguy, H. Elangovan, R. Saraf, V. Maheshwari, A. Kumar, A. Sehirlioglu, and Y. Ivry,
Affiliations : C. Saguy: Solid State Institute, Technion ? Israel Institute of Technology, Haifa 32000, Israel H. Elangovan and Y. Ivry: Department of Material Sciences and Engineering, Technion ? Israel Institute of Technology. Haifa 32000, Israel R. Saraf and V. Maheshwari: Department of Chemistry, Waterloo Institute of Nanotechnology, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada A. Sehirlioglu: Department of Materials Science and Engineering, Case Western Reserve University, Cleveland, OH 44106, United States

Resume : We utilized in-situ thermal, electric-field and illumination excitations to expose the domain-scale, origin of functionality in ferroelectric systems that exhibit augmented electromechanical and photoelectric properties. Specifically, using variable-temperature piezoresponse microscopy, direct imaging of the nanodomain dynamics and local hysteresis spectroscopy measurements in the seminal relaxor PMN-PT, demonstrated the role of these nanodomains around the ferroelectric-to-paraelectric transition. Likewise, introducing variable-temperature photoconductive atomic force microscopy, revealed that the origin of photoconductivity in the seminal hybrid-halide perovskite, MAPbI3 is the existence of polar domains [1]. The mechanisms in which ferroelectric domains contribute to the material functionality will also be discussed. [1] R. Saraf, C. Saguy, H. Elangovan, V. Maheshwari and Y. Ivry, Appl. Phys. Lett. 118, 151903 (2021)

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09:00 Plenary Session    
12:30 Lunch    
Session 14:00 - 15:30 : Chair - Philippe Ghosez
Authors : S. Kamba1, A. Maia1, M. Savinov1, P. Ondrejkovič,1 C. Kadlec1, M. Míšek1, J. Kaštil,1 A. A. Belik2
Affiliations : 1Institute of Physics of the Czech Academy of Sciences, Na Slovance 2, 182 21 Prague 8, Czech Republic; 2International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS), Namiki 1-1, Tsukuba, Ibaraki 305- 0044, Japan

Resume : Recently, it was reported that the cubic quadruple perovskite BiMn3Cr4O12 exhibits subsequent ferroelectric and antiferromagnetic phase transitions at 135 K and 125 K. Moreover, second magnetic phase transition associated with the antiferromagnetic order of the Mn3+ spins occurs at 48 K and it is accompanied by a 20% increase in ferroelectric polarization due to a strong magnetoelectric coupling. For that reason, Zhou et al. [1] concluded that BiMn3Cr4O12 exhibits features of both type-I and type-II multiferroicity. Here, we report heat capacity, magnetic and low-frequency dielectric properties together with IR, THz, and Raman spectra of BiMn3Cr4O12 ceramics. The IR and THz spectra reveal a polar soft phonon near 26 cm-1 at 300 K, whose softening down to 13 cm-1 is responsible for the ferroelectric phase transition, confirming the theoretical prediction that this transition is of the displacive type.[2] Furthermore, the optical mode softens according to the Cochran law towards 125 K and the Curie-Weiss fit of dielectric permittivity also results in ferroelectric TC = 125 K. Since only one anomaly in heat capacity is seen near 125 K [1], we propose that both magnetic and ferroelectric transitions coincide. It seems that the structural phase transition triggers the antiferromagnetic order of Cr3+ magnetic moments due to variation of exchange striction interaction. Detailed pyrocurrent and magnetization studies allow to distinguish between intrinsic and extrinsic contributions in polarization, as well as to determine the values of electrocaloric and magnetocaloric effects near the phase transitions. Raman spectra reveal a deviation of the temperature dependence of some phonon frequencies from the classical anharmonic behavior due to spin-phonon coupling below 130 K. The observed phonon activities in Raman and IR spectra are compared with the predictions from factor-group analysis and first-principles calculations. [2, 3] [1] L. Zhou et al., Advanced Materials 29, 1703435 (2017) [2] J. Q. Dai and C. C. Zhang, J. Amer. Ceram. Soc. 102, 6048 (2019) [3] J.Q. Dai, X.L. Liang, and Y.S. Lu, Chem. Phys. 538, 110924 (2020)

Authors : L. Ponet, S. Artyukhin, Th. Kain, J. Wettstein, S.-W. Cheong, M. Mostovoy, A. Pimenov
Affiliations : Italian Institute of Technology, Genova, Italy; Vienna University of Technology, Austria; Rutgers University, New Jersey, USA; University of Groningen, Netherlands; Vienna University of Technology, Austria

Resume : Electric control of magnetism and magnetic control of ferroelectricity can improve energy efficiency of magnetic memory and data processing devices. However, the necessary magnetoelectric switching is hard to achieve, and requires more than just a coupling between spin and charge degrees of freedom. We show [1] that an application and subsequent removal of a magnetic field reverses the electric polarization of the multiferroic GdMn2O5, thus requiring two cycles to bring the system back to the original configuration. During this unusual hysteresis loop, four states with different magnetic configurations are visited by the system, with one half of all spins undergoing unidirectional full-circle rotation in increments of ~90 degrees. Therefore, GdMn2O5 acts as a magnetic crankshaft converting the back-and-forth variations of the magnetic field into a circular spin motion. This peculiar four-state magnetoelectric switching emerges as a topologically protected boundary between different two-state switching regimes. Our findings establish a paradigm of topologically protected switching phenomena in ferroic materials. [1] L. Ponet, S. Artyukhin, Th. Kain et al., Nature (2022) doi: 10.1038/s41586-022-04851-6

Authors : P. Pappas1, A. Bussmann-Holder2, H. Keller3, E. Liarokapis1, and K. Roleder4
Affiliations : 1- Department of Physics, National Technical University of Athens, Athens 15780, Greece; 2-Max-Planck-Institute for Solid State Research, Heisenbergstr.1, D-70569 Stuttgart, Germany; 3-Physik-Institut der Universität Zürich, CH-8057 Zürich, Switzerland; 4-Institute of Physics, University of Silesia, ul. 75 Pułku Piechoty 1, 41-500 Chorzów, Polande

Resume : Some novel puzzling and unexplained observations regarding the cubic to “tetragonal” phase transition at TS=282K in the almost multiferroic perovskite EuTiO3 have been reanalyzed in order to obtain deeper insight into the true structure and magnetic activity evolving below TS. For this purpose earlier and new birefringence [1] and high resolution XRD data [2] have been used where zero magnetic field data are compared to data under the influence of a direction dependent magnetic field. The XRD structural data have been taken as input to derive the magnetic exchange constants, the related Néel temperatures TN and the energies of the possible magnetic ground states. Taken both results together we conclude that below TS the symmetry cannot be tetragonal but only monoclinic followed by another symmetry lowering transition around T*≈210K. Furthermore, the exchange interactions, TN, and the energies evidence that any kind of magnetism stems from a competition of the various ground state energies and must be a consequence of frustration. References 1. Bussmann-Holder, A. et al. Transparent EuTiO3 films: A possible two-dimensional magneto-optical device. Sci. Rep. 7, 40621 (2017). 2. Bussmann-Holder, A., Liarokapis, E., & Roleder, K. Intriguing spin-lattice interactions in EuTiO3. Sci. Rep. 11, 18978 (2021).

15:30 Coffee break    
Session 16:00 - 17:15 : Chair - Annette Bussmann-Holder
Authors : Manuel Bibes
Affiliations : Unité Mixte de Physique CNRS/Thales

Resume : Just as the apparent incompatibility between ferroelectricity and magnetism prompted the renaissance of multiferroics1, the research on « ferroelectric » metals – conjectured in the 1960s by Anderson and Blount2 – was recently revitalized. Yet, their experimental demonstration remains very challenging due to the contra-indication between the presence of free charge carriers and switchable electric dipoles. In this talk we will report on two-dimensional electron gases (2DEGs) formed on Ca-substituted SrTiO3 (STO). Signatures of the ferroelectric phase transition near 30 K are visible in the temperature dependence of the sheet resistance RS and in a strong, reproducible hysteresis of RS with gate voltage3. In addition, spectroscopic explorations of the 2DEG region indicate the presence of switchable ionic displacements. Beyond their fundamental interest in materials physics, ferroelectric 2DEGs offer opportunities in spin-orbitronics: we will show how their spin-charge conversion properties, caused by the inverse Rashba-Edelstein effect, can be electrically tuned in amplitude and sign in a non-volatile way4. These results open the way to a whole new class of ultralow-power spin-orbitronic devices operating without the need for magnetization switching. Finally, I will show how one can introduce magnetism into such systems to achieve multiferroic 2DEGs displaying magnetoelectric coupling. 1 N.A. Hill, J. Phys. Chem. B 104, 6694 (2000). 2 P.W. Anderson and E.I. Blount, Physical Review Letters 14, 217 (1965). 3 J. Bréhin et al, Phys. Rev. Materials 4, 041002 (2020). 4 P. Noël et al, Nature 580, 483 (2020).

Authors : Danila AMOROSO (1), Georgy GORDEEV (2), Bertrand DUPE (1), Mael GUENNOU (2), Matthieu VERSTRAETE (1)
Affiliations : (1) Université de Liège, NanoMat/Q-mat/CESAM, B-4000 Liège, Belgium ; (2) University of Luxembourg, Department of physics and materials science, 41 rue du Brill, 4422 Belvaux, Luxembourg

Resume : Magnetic Rare-earth orthoferrites RFeO3 exhibit a rich playground ranging from multiferroicity to spin-reorientation, strong magnetostriction and ultrafast light-driven manipulation of magnetism, which can be exploited in spintronics. Such properties stem from the strong spin-orbit coupling (SOC) interaction combined with lattice vibrations (phonons) due to the presence of two magnetic ions (R3+, Fe3+) in different sublattices. This is the case, for instance, in SmFeO3, where recent experiments attempted to clarify its non-collinear ground-state, the origin of its spin-reorientation and low-temperature magnetization compensation. Particularly, anomalous evolutions of vibrational modes, the emergence of new modes and possible electro-magnons have been detected in Raman spectroscopy. Nevertheless, a conclusive picture has not yet been achieved, and theoretical studies to clarify microscopic mechanisms at play are still rare. Here, combining Raman spectroscopy and fully non-collinear first-principles simulations, we explore the interplay between magnetic states and phonons. We highlight the fundamental role of the Sm f-orbital SOC in the magnetic and structural anisotropies, and samarium’s contribution to the spin-phonon coupling.

Authors : M A Carpenter1, D Pesquera1, D O’Flynn2,8, G Balakrishnan2, N Mufti3,4, A A Nugroho3,9, T T M Palstra3, M Mihalik Jr5, M Mihalik5, M Zentková5, A Almeida6, J Agostinho Moreira6, R Vilarinho6 and D Meier7
Affiliations : 1 Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, United Kingdom. 2 Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom. 3 Solid State Chemistry Laboratory, Zernike Institute for Advanced Materials, Rijksuniversiteit Groningen, Nijenborgh 4, 9747AG Groningen, The Netherlands. 4 Department of Physics, Universitas Negeri Malang, Jl. Semarang No.5, Malang, 65145 Indonesia, Indonesia. 5 Institute of Experimental Physics, Slovak Academy of Sciences, Watsonova 47, Kosice, Slovakia. 6 IFIMUP, Departamento de Física e Astronomia, Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal. 7 Department of Materials Science and Engineering, NTNU Norwegian University of Science and Technology, 7491 Trondheim, Norway.

Resume : Rare-earth orthomanganites are outstanding compounds because they exhibit macroscopic properties arising from the correlation between spins, charge, orbital and lattice degrees of freedom. Among them, only TbMnO3 and DyMnO3 have Mn–O–Mn bond angles which fall in the narrow range that is required for multiferroic properties where ferroelectricity arises from cycloidal magnetism [1]. GdMnO3 has attracted much attention with the aim to strain-engineering its properties [2], as its Mn-O-Mn bond angle sets it at the border line, next to spontaneous multiferroics TbMnO3 and DyMnO3. It is clear that sensitivity to the A-site cation size and the lattice distortions which follow, are a vital component of the structural and magnetic stability relationships even though strain is not the functional property of primary interest. This contribution addresses the experimental study of elastic and anelastic properties across the low temperature magnetic phase transitions in GdMnO3 and TbMnO3 through a temperature dependent resonant ultrasound spectroscopy in the 100 kHz - 2 MHz range [3]. The comparison of the temperature dependence of the elastic moduli and acoustic losses, and their anomalous behaviour across the magnetic phase transitions of GdMnO3 and TbMnO3 enable us to get information concerning the strain/magnetic order parameter coupling form, and the effect of the specific magnetic ordering on this interaction. Magnetoelastic loss peaks at lower temperatures demonstrate that aspects of the magnetoelectric structure remain mobile down to at least ∼5 K. The results clearly evidence the key role of the magnetism on the strain properties of these materials. This contribution will also address the implications of the coupling between strain, magnetic and electric dipoles in thin films and multiferroic domain walls. References: [1] T. Goto, et al., Phys. Rev. Lett. 92, 257201 (2004) [2] P. Machado, et al., Scientific Reports 9, 18755 (2019). [3] M. A. Carpenter et al., J. Phys.: Condens. Matter 33, 125402 (2021).

Authors : R. Vilarinho1, R. Vilão2, A. Apostolos2, S. Savvin3, C. Ritter3, Z. Guguchia4, R. Scheuermann4, M. Mihalik5, M. Zentkova5 and J. Agostinho Moreira1
Affiliations : 1IFIMUP, Dep. de Física e Astronomia, Fac. de Ciências da Universidade do Porto, Portugal 2Department de Física, Universidade de Coimbra, Portugal 3Institute Laue Langevin (ILL), 38000 Grenoble, France 4Paul Scherrer Institute (PSI), 5232 Villigen, Switzerland 5Institute of Experimental Physics Slovak Academy of Sciences, Watsonova 47, Košice, Slovak Republic

Resume : Rare-earth orthomanganites (RMnO3) and orthoferrites (RFeO3) have renewed the scientific interest due to their remarkable magnetic properties, spin-reorientation transitions and, more recently, by the discovery of low-temperature ferroelectricity and multiferroicity in some of them [1]. While in the RMnO3, the Mn3+ spins present a TN typically below 50 K, into magnetically ordered phases that strongly depend on the rare-earth, in the RFeO3, the Fe3+ spins have a TN above 600 K into a common canted AFM phase [1]. Despite being heavily studied materials, there are recent reports of a deviation to the Curie-Weiss law in the paramagnetic phase of TbMnO3 well above TN (between 150 and 200 K), accompanied by a negative thermal expansion of the c-axis, and anomalies on the optical phonon energies measured by THz, FTIR and Raman spectroscopies [2]. This magnetostructural effect has been interpreted on the basis of short-range magnetic ordering and/or crystal-field excitations of the Tb3+ cation. In this work, we study both TbMnO3 and TbFeO3, showing that similar anomalies on the magnetization, lattice parameters and phonon energies, to those observed in the paramagnetic phase of TbMnO3, also occur in TbFeO3 at the same temperatures, well within its antiferromagnetic phase [3]. Combining neutron powder diffraction obtained at ILL and Raman spectroscopy, we show this magnetostructural effect is a result of shift of oxygen positions below 200 K, which further increase the octahedra rotation angle by 0.15º in TbFeO3. We also show that in other RMnO3 and RFeO3 such anomalies are not found. To understand whether short-range magnetic ordering or crystal-field excitations underlie this phenomenon, we performed muon spin spectroscopy on TbMnO3 at PSI. For this, we take advantage of using the muons to measure the local magnetic fields through the Knight shift, at 1 Å distance from the oxygen position. Our results show that, although the local magnetic field increases below 200 K, the Knight shift is perfectly scaled by a paramagnetic law down to TN = 40 K. This result allows us to conclude that no short-range order occurs in the paramagnetic phase of TbMnO3 that would explain the observed magnetostructural effect. We then suggest that in fact an interplay between the oxygen position and the crystal-field excitation levels of the Tb3+ occurs, leading to a further deformation of the crystallographic structure, which then affects the macroscopic magnetic properties. [1] T. Kimura et al., Nature 426, 6962 (2003); E. Bousquet et al., JPCM 28, 123001 (2016) [2] K. Berggold et al., PRB 76, 094418 (2007); D. O'Flynn JPCM 26, 256002 (2014); S. Mansouri et al., JPCM 30, 175802 (2018) [3] R. Vilarinho et al., Scientific Reports, in press (2022)

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Session 9:30 - 10:30 : Chair - Manuel Bibes
Authors : Rebecca Kelly, Olivia Baxter, Bogdan Zhigulin, Amit Kumar, Marty Gregg, Raymond McQuaid
Affiliations : Centre for Nanostructured Media School of Mathematics and Physics Queen's University Belfast Belfast BT7 1NN U.K.

Resume : Scanning Thermal Microscopy (SThM) is a promising Atomic Force Microscopy technique for mapping the thermal properties of materials at the nanoscale; surface temperature distributions can typically be mapped out with temperature resolution on the order of 10 mK and with spatial temperature resolution that is sub-100nm. In this talk, I will discuss how SThM could be a powerful tool for studying the role of microstructure on heat flow in ferroelectric materials, specifically for (i) mapping the thermal properties of domain walls and (ii) understanding the microscopic behaviour of electrocaloric effects. Interest in using ferroic domain boundaries to enable active control of heat flow has been steadily growing over the last decade. Domain walls are already known to inhibit thermal transport through phonon scattering [1] and the fact that some domain walls can exhibit enhanced electrical conductivity suggests that enhanced thermal transport within the wall is also a possibility. However, direct, local measurements of either of these domain wall thermal behaviours have yet to be reported. In this talk, I will describe our efforts to locally map variations in thermal response associated with such microstructural inhomogeneity. Similar to the approach used in [2], a thin gold bar deposited on the sample surface is periodically Joule heated and the resulting temperature oscillations are mapped by using the scanning probe as a temperature sensor. To validate that spatial variations in the thermal properties of the underlying sample of interest can be imaged, we attempt to image thermal contrast across the metal/dielectric layers of a multilayer ceramic capacitor (MLCC). Our attempts to image the thermal response of conducting domain walls in LiNbO3 using this approach will also be discussed. The electrocaloric effect is a well-known phenomenon where adiabatic application of an electric field to a ferroelectric material results in a temperature change. While it can be well described macroscopically through thermodynamics, and is understood to arise fundamentally from changes in dipolar configurational entropy, the effect is not as well characterised at the microstructural level [3]. In this regard, we build on previous SThM based studies [4] and demonstrate how local electrocaloric response can be imaged with sub-micron spatial resolution, here demonstrated in a MLCC. Using this approach, 2D spatially resolved maps of electrocaloric heating and cooling can be generated. We intend to further use this technique to elucidate the influence of microstructural inhomogeneity on electrocaloric response in other material systems. [1] Ihlefeld, J. et al. Nano Lett. 15, 1791 (2015); Langenberg, E. et al. Nano Lett. 19, 7901 (2019). [2] Menges, F. et al. Nat. Commun. 7, 1, (2016). [3] Y. Liu, Appl. Phys. Rev. 3, 031102 (2016). [4] Kar-Narayan, S. et al. Appl. Phys. Lett. 102, 032903 (2013); Shan, D. et al. Nano Energy 67, 104203 (2020).

Authors : Constance Toulouse 1, Mael Guennou 1, Jens Kreisel 1, Jean-Nicolas Audinot 2, Alfredo Blázquez Martinez 2, Torsten Granzow 2, Sebastjan Glinšek 2, Veronika Kovacova 2, Emmanuel Defay 2, Saeedeh Farokhipoor 3, Beatriz Noheda 3, Johanna Fischer 4, Vincent Garcia 4, Stéphane Fusil 4, Lluis Yedra Cardona 5
Affiliations : 1 - Department of Physics and Materials Science, University of Luxembourg, Luxembourg; 2 - Luxembourg Institute of Science and Technology, Luxembourg; 3 - Zernike Institute for Advanced Materials, University of Groningen, The Netherlands; 4 - Unité Mixte de Recherche CNRS-Thales, France; 5 - Department of Electronics and Biomedical Engineering, University of Barcelona, Spain

Resume : Functional properties that can, for instance, be of electrical, magnetic, or elastic origin and that can be used in applications have driven materials science research in the past decades. Multifunctional materials, in particular, that exhibit several functional properties simultaneously which can be coupled together, are of even higher applicative interest, notably for their transducing possibilities. The control and tunability of functional properties have been increasingly investigated, including the possibility of tuning properties under strain. In particular, epitaxial strain, which is now routinely implemented, has yielded numerous ground-breaking results, especially in multiferroic materials [1,2]. We present here a novel strain engineering technique, based on Helium implantation, that allows to obtain an effective negative pressure in implanted materials, making it available to probe entirely new regions of materials’ phase diagrams. We first studied the structural effect of Helium implantation in epitaxial thin films of BiFeO3, a model multiferroic compound exhibiting multiferroicity well above room temperature. We demonstrated the effective negative pressure effect and showed that we could increase the lattice parameter of the films under implantation. We could trigger the structural transition towards the supertetragonal polymorph with increasing Helium dose, achieving an increase of the out-of-plane lattice parameter of up to 8.9% [3]. We now focus on structurally-textured sol-gel films, less costly to produce and more suited for application processes, where we demonstrate the tunability of functional properties. In BiFeO3, we show the influence of Helium implantation on the ferroelectric properties. We modify significantly the coercive field (up to 68% increase) and the low-field conductivity of the films under Helium dose (two orders of magnitude decrease at higher Helium dose), as well as the piezoresponse force microscopy (PFM) signal of the implanted regions. References: [1] Infante et al., Phys. Rev. Lett. 105, 057601 (2010) [2] Sando et al., Nature Materials 12(7), 641-646 (2013) [3] Toulouse et al., Phys. Rev. Materials 5, 024404 (2021)

10:30 Coffee break    
Session 11:00 - 12:30 : Chair - Raymond McQuaid
Authors : Xavier Moya
Affiliations : Department of Materials Science, University of Cambridge

Resume : A quarter of the UK’s CO2 emissions can be attributed to space heating and cooling. This is primarily due to heating with natural gas and cooling with compression of greenhouse gases, which are neither environmentally friendly nor energy efficient. Therefore there is great interest in developing energy-efficient solid-state heat pumps that can replace these environmentally damaging technologies. Barocaloric materials are at the core of novel solid-state heat-pump technologies. During this talk I will describe our work on mechanically responsive barocaloric materials for heating and cooling applications.

Authors : Mączka, M.*(1), Gągor, A.(1), Ptak, M.(1), Sobczak, S.(2), Katrusiak, A.(2), Fedoruk, K.(3), Sieradzki, A.(3), Zaręba, J.K.(4)
Affiliations : (1)Institute of Low Temperature and Structure Research, Polish Academy of Sciences, 50-422 Wrocław, Poland (2)Faculty of Chemistry, Adam Mickiewicz University, 61-614 Poznań, Poland (3)Department of Experimental Physics, Wrocław University of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370, Wrocław (4)Institute of Advanced Materials, Wrocław University of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370, Wrocław

Resume : Hybrid organic-inorganic have been extensively studied for their tuneable properties such as photovoltaic, photoluminescent, switchable dielectric or ferroelectric. Properties of these materials are often induced or tuned by onset of structural phase transitions. Therefore, in order to obtain deep insight into phase transition mechanisms and structure-property relation, temperature-dependent studies are usually performed. However, pressure is emerging as another external parameter that can be used for tuning crystal structures and properties of hybrid perovskites. For instance, the application of pressure can enhance existing properties or lead to discovery of polymorphs with novel functional properties. Recently, we have discovered that methylhydrazinium cation (MHy+) can be used for synthesis of both 3D (MHyPbX3, X=Cl, Br) and 2D (MHy2PbX4, X=Cl, Br, I) perovskites, which exhibit multiple linear and non-linear optical phenomena [1-4]. Furthermore, MHy2PbBr4 is a ferroelectric materials with high Tc~351 K [4]. In this talk, I will present results of temperature- and pressure-dependent studies of methylhydrazinium-based lead halide perovskites. In particular, I will show that centrosymmetric MHy2PbI4 transforms at higher pressure to a ferroelectric Pmn21 phase, which is stable for the bromide at ambient conditions. Thus, pressure induces ferroelectricity in the studied compound. Interestingly, on further compression both MHy2PbBr4 and MHy2PbI4 exhibit unprecedented type of structural phase transitions into P21 phases, when MHy+ cations are pushed into the gaps in inorganic layers. This transport of counter cations leads to a significant increase of Pb-NH2 interactions, an unprecedented three-fold increase of positive linear compressibility along the layer stacking direction and large negative linear compressibility along the stacking direction, not reported for any 2D analogue. Acknowledgements: This research was supported by the National Science Center (Narodowe Centrum Nauki) in Poland under the project no. 2018/31/B/ST5/00455. [1] M. Mączka, M. Ptak, A. Gągor, D. Stefańska and A. Sieradzki, Chem. Mater. 31, 8563 (2019). [2] M. Mączka, M. Ptak, A. Gągor, D. Stefańska, J. K. Zaręba and A. Sieradzki, Chem. Mater. 32, 1667 (2020). [3] M. Mączka, A. Gągor, J. K. Zaręba, D. Stefańska, M. Drozd, S. Balciunas, M. Simenas, J. Banys and A. Sieradzki, Chem. Mater. 32, 4072 (2020). [4] M. Mączka, J. K. Zaręba, A. Gągor, D. Stefańska, M. Ptak, K. Roleder, D. Kajewski, A. Soszyński, K. Fedoruk and A. Sieradzki, Chem. Mater. 33, 2331 (2021).

Authors : Yuzhong Hu, Marin Alexe, Minming Yang, Hong Jin Fan, Lu You, Junling Wang, Pooi See Lee
Affiliations : University of Warwick

Resume : Organic-inorganic hybrid ferroelectrics (OIHF) are a new member of ferroelectrics family which comprised of both organic and inorganic parts as building block. Since 2014, tens of OIHF structures have been explored with striking progress made in electromechanical properties such as high ferroelastic strain output and piezoelectricity. Recently, two orders of magnitude higher strain (21.5%) and d33 (1540 pC/N) higher than those of Lead zirconate titanate (PZT) were achieved in OIHF, suggesting their bright future as lightweight and high-performance electroactive materials. Different with widely used piezoelectric enhancement methods such as morphotropic phase boundary (MPB) effect in piezoelectric ceramics, the approach for OIHF to realize these excellent electromechanical are involved with special molecular and bond engineering. With our work, I will introduce the space-confinement method and molecular engineering strategy that are employed to realize non-180 degree ferroelastic switch and thus achieved large strain and piezoelectricity in hybrid systems. Reference: Hu, Yuzhong, et al. "Ferroelastic-switching-driven large shear strain and piezoelectricity in a hybrid ferroelectric." Nature Materials 20.5 (2021): 612-617.

Affiliations : Université de Liège, Nanomat lab, Q-Mat center, CESAM Research Unit, Allée du 6 août, 19, 4000 Liege, Belgium

Resume : There is currently an increasing enthusiasm towards long-range magnetic order and multiferroicity in two-dimensional (2D) materials both from the fundamental and applicative point of view. In this respect, by means of first-principles-based simulations, we investigated magnetic properties in a single-layer of some of the triangular 3d transition metal dihalides [1], which belong to the promising class of van der Waals materials, with a special focus on the exotic NiI2 case [2,3]. Through also supporting Monte Carlo simulations, we show that a thermodynamically-stable skyrmionic lattice with a well-defined topology and chirality of the spin texture in absence of Dzyaloshinskii?Moriya (DM) and Zeeman interactions, can be stabilized by the anisotropic part of the short-range symmetric exchange, related to the relevant spin-orbit coupling (SOC) of the heavy ligands, assisted only by the exchange frustration. In detail, the symmetric anisotropic exchange tensor, also referred to as two-ion anisotropy (TIA), shows large off-diagonal terms, which - due to the peculiar non-coplanar arrangement of the spin-ligand plaquettes- induce frustration in the relative orientation of spins by setting non-coplanar principal axes. Combined with the exchange frustration from competing ferromagnetic first- and antiferromagnetic third-neighbor interactions, this results in a not-trivial spin-configuration with well-defined topology, making the TIA acting as an emergent chiral interaction. Particularly, in the centrosymmetric NiI2 monolayer, we predicted a spontaneous high-Q antiskyrmionic lattice (|Q|=2) with fixed chirality, undergoing a topological phase transition, under magnetic field, to a more conventional skyrmion lattice (|Q|=1). Additionally, we predicted a competing noncollinear single-q helimagnetic state, exhibiting low-dimensional magnetoelectric and multiferroic properties. Such a multiferroic state in single-layer NiI2 has been also experimentally detected by combined birefringence and second-harmonic-generation measurements [4]. Such findings, on the one hand, propose a novel mechanism able to drive stabilization of topological spin structures in magnetic semiconductors with short-range anisotropic interactions. On the other hand, they open the street towards new low-dimensional magnetoelectrics and/or multiferroics. References: [1] K. Riedl, D. Amoroso et al. ?Microscopic origin of magnetism in monolayer 3d transition metal dihalides?. ArXiv:2206.00016 (2022) [2] D. Amoroso, P. Barone & S. Picozzi, ?Spontaneous skyrmionic lattice from anisotropic symmetric exchange in a Ni-halide monolayer?. Nature Communications 11, 5784 (2020) [3] D. Amoroso, P. Barone and S. Picozzi. ?Interplay between Single-Ion and Two-Ion Anisotropies in Frustrated 2D Semiconductors and Tuning of Magnetic Structures Topology?. Nanomaterials, 11(8), 1873 (2021) [4] Q. Song, [?] , D. A. et al. ?Evidence for a single-layer van der Waals multiferroic?. Nature, 601, 602 (2022)

12:30 Lunch    
Session 14:00 - 15:30 : Chair - Mirosław Mączka
Authors : Yoon Hyung Keum,Hyun Wook Shin,Jong Hwa Son,Jong-Soo Rhyee,Jong Yeog Son
Affiliations : Yoon Hyung Keum1;Hyun Wook Shin1;Jong Hwa Son2;Jong-Soo Rhyee1,2;Jong Yeog Son1,2 1. Kyunghee University, Yongin-Si, Gyeonggi-Do, Korea (the Republic of). 2. V-memory Corp., Yongin-Si, Gyeonggi-Do, Korea (the Republic of).

Resume : Ferroelectric domain walls (DWs) formed at the boundaries between domains have been reported for electrically conductive phenomena. Since DW can be artificially controlled by external electric field and structure, DWC non-volatile memory application is possible by forming and removing DW with high DW conductivity (DWC). Here, we introduce the recent research results related to DWC non-volatile memories and present the recent research results of our research group. We fabricated and evaluated two types of DWC nonvolatile devices with two electrodes and three electrodes using epitaxial PbTiO thin films on single crystal (100) Nb:STO substrates. For the two-electrode device, the change of the current-voltage curves was investigated depending on the formation of the ferroelectric domain walls. As for the resistance of DWC, a systematic increase in current was observed as DW was changed to 0, 2, and 4. In particular, in a threeelectrode DWC nonvolatile device having three electrodes having a structure similar to that of a flash memory, the state of the source-drain currents could be changed into two states by the gate voltage. In addition, the source-drain currents exhibited a nonvolatile memory characteristic in which a low current state and a high current state were maintained even when a gate voltage was not applied. Research results on two types of DWC non-volatile devices having two electrodes and three electrodes may provide opportunities for new nonvolatile memory devices that can replace the existing flash memory.

Authors : Oksana Mys, Myroslav Kostyrko, Dmytro Adamenko, Iryna Martynyuk-Lototska, Ihor Skab, Rostyslav Vlokh
Affiliations : O. G. Vlokh Institute of Physical Optics, 23 Dragomanov Street, 79005 Lviv, Ukraine

Resume : We have shown that the existence of optical activity enhances significantly the acousto-optic (AO) figure of merit. The effect arises due to nonzero ellipticity of the interacting optical eigenwaves. More specifically, the above enhancement takes place because additional elasto-optic (EO) tensor components become superimposed in the effective EO coefficient. The latter just occurs because the ellipticity of the optical eigenwaves approaches unity in the vicinity of optic axis. Using the Pb5Ge3O11 crystals as an example, we have demonstrated that enhancement of the efficiency of AO diffraction is always typical for all the types of isotropic and anisotropic AO interactions, whenever the incident optical wave propagates close to the optic axis. In the particular case of diffraction in the interaction plane XZ of Pb5Ge3O11 crystals, the maximal enhancement of the AO figure of merit takes place under conditions of the isotropic diffraction of ordinary and extraordinary optical waves with a pure transverse acoustic wave polarized parallel to the Y axis (a so-called AW PT2), with the AO figure of merit increasing from zero up to 7.5×10?17 s3/kg, and the types of anisotropic AO diffraction on the transverse (PT2) and quasi-transverse QT1 acoustic waves, when the AO figure of merit increases twice (e.g., from 7.6×10?17 up to 1.5×10?16 s3/kg). The maximal AO efficiency in the interaction plane XZ is reached at the types I and II of the isotropic AO interactions of ordinary and extraordinary optical waves with a quasi-longitudinal acoustic wave. In these cases, due to a nonzero ellipticity of optical eigenwaves, the AO figure of merit in these cases increases respectively from 6.8×10?15 up to 12.4×10?15 s3/kg and from 5.6×10?15 to 12.4×10?15 s3/kg. The results of theoretical analysis have been proved experimentally by the studying EO coefficients for the Pb5Ge3O11 crystals at the optical wavelength 632.8 nm, using the Dixon?Cohen method for the case of isotropic AO interaction between circularly polarized optical waves and a quasi-longitudinal (QL) acoustic wave propagating along the X axis. It is supposed that the AO efficiency can be enhanced not only in the non-centrosymmetric chiral crystals revealing the natural optical activity. Centrosymmetric materials can also manifest induced optical activity which is due to either the Faraday effect or electrogyration. To achieve these situations, a magnetic or electric field must be applied along the optic axis. This leads to practical possibilities for operating the efficiency of AO diffraction with the external electric and magnetic fields.

Authors : I. Lazar (1), A. Majchrowski (2), R. W. Whatmore (3), A. M. Glazer (4,5), R. Sitko (1), D. Kajewski (1), J. Koperski (1), A. Soszy?ski (1), K. Roleder (1)
Affiliations : (1) Institute of Physics, University of Silesia, Chorzów, Poland; (2) Institute of Applied Physics, Military University of Technology, Warszawa, Poland; (3) Department of Materials, Faculty of Engineering, Imperial College London, London, SW7 2AZ, United Kingdom; (4) Clarendon Laboratory, University of Oxford, Oxford, OX1 3PU, United Kingdom; (5) Department of Physics, University of Warwick, Coventry, CV4 7AL, United Kingdom;

Resume : PbZr1-xTixO3 (PZT) solid solutions occupy an exceptional position among the perovskite-structured materials because of their many practical applications. In this work, we report the grown PZT single crystals with 0?x?0.13 and good Ti homogeneity. Recent studies describe new phases [1-4] and significantly modify Jaffe's diagram [5]. Because most reports on the phase diagram of PZT solid solutions were constructed based on investigations of ceramics, mainly due to technological difficulties in growing the PZT single crystals, we undertook investigations of the Zr-rich PZT single crystals. Based on dielectric and optical studies, the tricritical point was confirmed for x close to 0.06 [6]. Temperature changes of the optic, dielectric, and strain properties of the PZT single crystal have confirmed the existence of additional phase transitions. Earlier, additional phase transitions have been reported above x>0.06 for ceramics [1]. In PZT crystals, such additional transition has been observed already in a PbZr0.95Ti0.05O3 single crystal. [1] F. Cordero, F. Trequattrini, F. Craciun and C. Galassi, Phys. Rev. B 87, 094108 (2013). [2] M. J. Li, L. P. Xu, K. Shi, J. Z. Zhang, X. F. Chen, Z. G. Hu, X. L. Dong and J. H. Chu, J. Phys. D:Appl. Phys. 49, 275305 (2016). [3] N. Zhang, H. Yokota, A. M. Glazer, D. A. Keen, S. Gorfman, P. A. Thomas, W. Rena and Z.-G. Ye, IUCrJ 5,1 (2018). [4] N. Zhang, H. Yokota, A. M. Glazer, Z. Ren, D. A. Keen, D. S. Keeble, P. A. Thomas and Z. - G. Ye, Nat. Commun. 5, 5231 (2014). [5] B. Jaffe, W. R. Cook and H. Jaffe, Piezoelectric Ceramics, Academic, London (1971). [6] R. W. Whatmore, R. Clarke and A. M. Glazer, J. Phys. C: Solid State Phy.s, 11, 3089 (1978). Acknowledgements: This work was supported by the National Science Centre, Poland, grant number 2020/37/B/ST3/ 02015

Authors : Mariana M. Gomes1, Abdrrazzak A. Bassou2, Manjunath Balagopalan1, Rui Vilarinho1, Bruna Silva3, João Oliveira3, Bernardo Almeida3, Pedro Tavares2, Abílio Almeida1 and J. Agostinho Moreira1
Affiliations : 1 IFIMUP, Departamento de Física e Astronomia da Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre s/n, 4169-007 Porto, Portugal 2 Centro de Química-Vila Real, ECVA, Chemistry Department, Universidade de Trás-os-Montes e Alto Douro, 5000-801 Vila Real, Portugal 3 CF-UM-UP, Departamento de Física, Universidade do Minho, Campus de Gualtar, 4710-057 Braga, Portugal

Resume : Rare-earth nickelates, RNiO3, are challenging compounds due to their intriguing physics, a consequence of the strong correlation between electronic, charge, spin and lattice degrees of freedom [1]. Among these compounds, NdNiO3 has raised some controversy regarding the nature of its metallic to insulator transition (MIT). NdNiO3 exhibits a first-order MIT, adopting a metallic and paramagnetic Pnma symmetry above TMI = 200 K and, in the insulating phase, transits into the P21/n symmetry, with the stabilization of a E’-type antiferromagnetic phase [2]. In RNiO3, a close relationship between structure and MIT has been proposed due to the strong dependence of the TMI from the rare-earth cation size [3]. The symmetry lowering at MIT is supposedly accompanied by NiO6 breathing distortion that once coupled to in-phase and anti-phase octahedra rotation distortions would trigger the MIT. However, contrarily to smaller rare-earth cations, in NdNiO3, the amplitude of these oxygen rotations is not enough to stabilize the charge ordering and open the bandgap of the eg-Ni orbitals, and the magnetic ordering helps to promote the occurrence of MIT [3]. Therefore, in NdNiO3, TNéel = TMI is expected. While some experimental studies evidence the concomitant nature between structure and MIT [4], others completely reject it, assigning the magnetic ordering to the triggering mechanism instead [5]. The question still remains concerning the mechanisms that actual trigger MIT in NdNiO3. Towards searching for an answer to this demand, we have carried out an experimental study in NdNiO3 ceramics and thin films of 260 nm and 110 nm deposited onto (001) oriented LaAlO3 substrate. In this work, we report temperature-dependent Raman scattering and magnetization measurements to follow the structure and magnetic order evolution across the MIT, which was identified from resistivity measurements. The experimental results point out for a decoupling between the structural and electronic orders but evidence a coupling between electronic and magnetic orders in NdNiO3, independently on the used sample type. [1] G. Catalan, Ph. Transit. 81, 729 (2008) [2] S. Catalano et al., Rep. Prog. Phys. 81, 046501 (2018) [3] A. Mercy et al., Nat. Commun. 8, 1 (2017) [4] J. Y. Zhang et al., Sci. Rep. 6, 23652 (2016) [5] D. Meyers et al., Sci. Rep. 6, 2793 (2016)

Authors : Simon Mellaerts, Jin Won Seo, Valeri Afans’ev, Michel Houssa, Jean-Pierre Locquet
Affiliations : Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium; Department of Material Engineering, KU Leuven, Kasteelpark Arenberg 44, 3001 Leuven, Belgium; Imec, Kapeldreef 75, 3001, Leuven, Belgium.

Resume : Complex oxides host a rich variety of functional phenomena - including multiferroicity, dielectricity, superconductivity, metal-insulator transition, and topology. Therefore, understanding these phenomena and their corresponding phase transition is of both fundamental and technological importance to further stimulate the search for novel material designs and manipulations. The latter pathway involves the epitaxial growth of these oxides with a lattice-mismatch-induced biaxial strain, which has led to the enhancement of these functional properties. In this work, we go beyond this conventional epitaxy and examine the use of a 3D stress/strain on these materials by first-principle methods. We focus on (negative) pressure-induced isosymmetric phase transitions – involving no change in their structural space group – in a ferroelectric (BaTiO3) and Mott (V2O3) material. For the former, we have shown the presence of a first-order transition upon negative pressure from its tetragonal phase to a novel supertetragonal polymorph with a c/a ratio of 1.3, resulting in unprecedent polarization values. On the other hand, V2O3 is well-known to have a room-temperature metal-insulator transition (MIT) upon Cr doping, however, we observe a similar MIT in pure V2O3 upon negative pressure. Both pressure-induced transitions show a discontinuity in their c/a ratio, which can be related to their corresponding distortion; c/a representing the tetragonal polar distortion for BaTiO3, while correlating to a trigonal distortion in V2O3. Firstly, a detailed density functional theory (DFT) study sheds light on how these structural discontinuities translate to their electronic and dielectric properties. Secondly, an ab initio local auxiliary atomic orbital description (crystal orbital Hamiltonian population analysis) is applied to study the changes in the chemical bonds associated with their structural distortion. We show that both structural discontinuities can be ascribed to a critical change in their orbital overlaps which triggers an abrupt electron re-ordering. Finally, it can be shown by Landau theory that all isosymmetric transition are a priori first-order in nature. Hence, we identify the general features of earlier-reported (pressure-induced) isosymmetric phase transitions, and unify these within this local atomic orbital description.

Authors : Andreas Ost, Alfredo Blazquez-Martinez, Emmanuel Defay, Sebastjan Glinsek
Affiliations : Materials Research and Technology Department, Luxembourg Institute of Science and Technology, 41 Rue du Brill, Belvaux L-4422, Luxembourg

Resume : Antiferroelectrics possess ordered dipole moments, which are arranged antiparallel so they cancel out within one unit cell. Upon application of sufficiently large electric field, ferroelectric phase is induced and characteristic double-hysteresis polarization loops can be measured. An archetypal antiferroelectric is PbZrO3, which is orthorhombic in its antiferroelectric phase and it is supposed to be rhombohedral in its ferroelectric phase. It is also a very complex material. For instance, thermodynamically stable ferrielectric phase was recently proposed in this material by first-principles studies [1]. Chemical Solution Deposition (CSD) is a well-known thin-film deposition technique, characterized by low cost, efficient scale-up and ability to produce high-quality polycrystalline thin films. Our group has been studying strongly (001)pc oriented polycrystalline PbZrO3 thin films prepared via CSD, with thicknesses ranging between 85 and 255 nm. Electromechanical properties were characterized on nanoscale using piezoresponse force microscopy and on macroscale by measuring polarization-electric field loops. In both cases presence of polar phase at low electric fields has been detected. While it could be of intrinsic origin, it could also arise from the presence of PbTiO3 (ferroelectric) seed layer, which was used to enhance crystallization of PbZrO3 and induce (001)pc orientation [2,3]. CSD has been traditionally seen as inferior technique for the growth of epitaxial films. In this contribution we will challenge this view by presenting our recent work on solution-grown epitaxial-like PbZrO3 thin films, which are deposited on Nb-doped (100) SrTiO3 substrates. According to theta-2theta X-ray diffraction the films are single-phase perovskites with mixed (120)o/(001)o out-of-plane orientation. Epitaxy is indicated by phi-scans corresponding to (110)o plane, in which four sharp peaks, separated by 90°, are observed. Polarization-electric field loops reveal antiferroelectric-ferroelectric phase transition at ~700 kV cm-1 and spontaneous polarization Ps of ~20 ?C cm-1. Smaller switching peaks are observed at low electric fields (~200 kV cm-1) with remanent polarization 2Pr of 10 ?C cm-2, pointing towards presence of polar phase. These peaks are rather minor in the pristine state and they become stronger with electric-field cycling. Further microstructural and electrical characterizations will be presented in the contribution and possible origins of the observed behaviour will be discussed. [1] H. Aramberri et al., NPJ Comp. Mater., 196 (2021). [2] H. Lu et al., Adv. Funct. Mater., 2003622 (2020). [3] C. Milesi-Brault et al., Appl. Phys. Lett, 118, 042901 (2020).

15:30 Coffee break    
Session 16:00 - 17:00 : Constance Toulouse
Authors : Pranab Parimal Biswas,1,3 Cosme Milesi-Brault1,2,3, Alfredo Blázquez Martínez,2,3 Naveen Aruchamy,2 Longfei Song,2 Veronika Kovacova,2 Sebastjan Glinsek,2,3 Torsten Granzow,2,3 Emmanuel Defay,2,3 Mael Guennou,1,3
Affiliations : 1Department of Physics and Materials Science, University of Luxembourg, L-4422 Belvaux, Luxembourg 2Materials Research and Technology Department, Luxembourg Institute of Science and Technology, L-4422 Belvaux, Luxembourg 3Inter-institutional Research Group on Ferroic Materials, L-4422 Belvaux, Luxembourg

Resume : Antiferroelectric materials exhibit electric field-induced phase transitions between anti-polar and polar states, which enable their use in energy storage capacitors and electrocaloric devices. Here, we investigate the effect of this phase transition on the birefringence change 1 mm thick polycrystalline PbZr0.95Ti0.05O3 film processed by chemical solution deposition on a transparent PbTiO3(13 nm)/HfO2(23 nm)/SiO2 substrate. We show that, despite the polycrystalline nature of the film and its moderate thickness, the field-induced phase transition produces a sizeable effect observable under a polarized microscope. The azimuthal angle-dependence and the time evolution of this field-induced birefringence are further discussed in order to better understand the observed effect. The study not only facilitates further understanding of the physics of the antiferroelectric phase transition but also opens the door for oxide antiferroelectric materials in electro-optic applications such as optical switching and display.

Authors : Subhajit Pal*, Emanuele Palladino, Haozhen Yuan, and Joe Briscoe
Affiliations : School of Engineering & Materials Science, Queen Mary University of London, London E1 4NS, United Kingdom

Resume : Photo-induced ferroelectric characteristics are receiving tremendous attention in research and technological aspects due to various fascinating phenomena exhibited by them, such as photovoltaic (PV), photostriction, photo-ferroelectric, and photo-electrocatalytic effects. In this regard, exploring the photo-induced multifunctional characteristics of ferroelectric materials is crucial for a detailed understanding of the dynamics associated with these phenomena and for implementing these characteristics in optoelectronic applications. Several advantages and drawbacks are associated with the ferroelectric system as shown by current research progress. For example, ferroelectric material exhibits anomalous PV response, which can be higher than the equivalent bandgap voltage. However, the wide-bandgap characteristic of ferroelectrics restricts the absorption of the solar spectra in the system, and therefore limits overall device efficiencies. To resolve some of the current issues, we plan to combine ferroelectric materials with conventional photo-absorbers. In this respect, porous BaTiO3 (pBTO) synthesis by spin coating technique is used as a substrate for electrodeposition, and the photo-absorber Fe2O3 is deposited on the pBTO thin film. The nanoscopic ferroelectric properties of the combined structure is demonstrated through piezoresponse force microscopy which exhibits typical ferroelectric behaviour. In this presentation, I will explain the outcomes of PV and photo-electrocatalytic characteristics of the combined system by tuning several external parameters such as porosity percentage, strain engineering, geometrical modification, etc. Overall, I will discuss a general overview of the current and future direction of the photo-induced ferroelectric characteristics for advanced optoelectronic applications.

Authors : Adil Alshoaibi, Osama Saber, Faheem Ahmed
Affiliations : Department of Physics, College of Science, King Faisal University, P.O. Box 400, Al-Ahsa 31982, Saudi Arabia

Resume : The present study aims to enhance the optical properties of barium titanate through narrowing its band gap energy to be effective for photocatalytic reactions in sunlight and be useful for solar cells. This target was achieved through growth of the hollandite phase instead of the perovskite phase inside the barium titanate crystals. By using solvent thermal reactions and thermal treatment at different temperatures (250 ◦C, 600 ◦C, and 900 ◦C), the hollandite phase of barium titanate was successfully obtained and confirmed through X-ray diffraction (XRD), Raman spectra and scanning electron microscopy techniques. XRD patterns showed a clear hollandite phase of barium titanium oxides for the sample calcined at 900 ◦C (BT1-900); however, the samples at 600 ◦C showed the presence of mixed phases. The mean crystallite size of the BT1-900 sample was found to be 38 nm. Morphological images revealed that the hollandite phase of barium titanate consisted of a mixed morphology of spheres and sheet-like features. The optical properties of barium titanate showed that its absorption edge shifted to the visible region and indicated band gap energy tuning ranging from 1.75 eV to 2.3 eV. Photocatalytic studies showed the complete and fast decolorization and mineralization of green pollutants (naphthol green B; NGB) in the prepared barium titanate with hollandite phase after illumination in sunlight for ten minutes. Finally, it can be concluded that the low band gap energy of barium titanate having the hollandite phase introduces beneficial structures for optical applications in sunlight.

Authors : Andrei N. Salak1, João Pedro Cardoso1, Vladimir V. Shvartsman2
Affiliations : 1 Department of Materials and Ceramics Engineering and CICECO – Aveiro Institute of Materials, University of Aveiro, 3810-193, Aveiro, Portugal; 2 Institute for Materials Science and CENIDE – Centre for Nanointegration Duisburg-Essen, University of Duisburg-Essen, 45141, Essen, Germany.

Resume : Lead-free perovskite solid solution systems with morphotropic phase boundary (MPB), which can be produced using conventional ceramic routes or crystal growth techniques, have already been investigated in detail and, in spite of numerous chemical modifications attempted, are hardly possible to make a real alternative to lead zirconate-titanate (PZT). In this respect, high-pressure synthesis is a fresh approach to search for new lead-free piezoelectrics and multiferroics. In the (1-x)BiMg0.5Ti0.5O3-xBiZn0.5Ti0.5O3 system [(1-x)BMT-xBZT], in which the orthorhombic BMT is a structural analogue of PbZrO3, while the tetragonal BZT is isostructural to PbTiO3, neither the end members nor their solid solutions can be obtained in bulk form using the conventional synthesis routes. The as-prepared (unannealed) compositions with a relative BZT content x < 0.75 are orthorhombic (space group Pnnm), while those with a BZT content above this value are tetragonal (P4mm). In the solution with x = 0.75, both phases coexist forming an MPB. We have recently revealed a phenomenon of annealing-stimulated irreversible transformations of the high-pressure stabilized phases (conversion polymorphism), and demonstrated that this is a new and promising approach to produce novel multiferroic materials. One of the most remarkable features of the high-pressure prepared complex perovskite compositions, which demonstrates the effect of conversion polymorphism, is that the patterns of their phase diagram depend on the maximum annealing temperature. This implies that by means of controlled annealing, materials with different combinations of the perovskite phases can obtained. This feature can be used, e.g., to design new materials with a morphotropic phase boundary. Annealing of the (1-x)BMT-xBZT samples at the temperatures below the decomposition points of their metastable perovskite phases (650-700oC depending on composition) was found to induce irreversible structural transitions of the perovskite phases over a wide compositional range. The compositions with 0.60 ≤ x ≤ 0.75 transform into the tetragonal structure upon heating and this structure remains upon cooling down to room temperature. The compositions with 0.20 ≤ x ≤ 0.60 irreversibly transform upon heating to the rhombohedral R3c structure. The compositions with x ≤ 0.10 keep the orthorhombic structure over the annealing. The new location of the MPB in the (1-x)BMT-xBZT system, where the rhombohedral and the tetragonal phases coexist, is at x = 0.60. The compositional dependence of the primitive perovskite unit-cell parameters is essentially similar to that of PZT. We report results of the in situ temperature X-ray diffraction study and the Piezoresponse Force Microscopy measurements. The results are discussed in comparison with those found in PZT. The authors acknowledge the financial support of the bilateral Portugal-Germany (FCT-DAAD) project PZT-FREE (grants 2021.09702.CBM and 57610755, respectively).


Symposium organizers
Anthony Michael GLAZER (Main organizer)University of Oxford

Clarendon Laboratory, Parks Road, Oxford OX1 3PU, UK
Guillaume NATAFCentre National de la Recherche Scientifique (CNRS)

University laboratory GREMAN, France
Krystian ROLEDERInstitute of Physics | University of Silesia

Uniwersytecka 4 40-007 Katowice Poland

+48 32 359 1478
Marek PAŚCIAKInstitute of Physics, Czech Acad. Sci.

Na Slovance 2, 182 21 Prague 8, CZ