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2015 Fall

Materials for electronics and optoelectronic applications away from silicon.


Ferroic perovskites for advanced materials

Physical properties of perovskite-based ferroics find applications in virtually all branches of functional materials. This symposium will gather researchers from a broad range of fields in order to discuss advances in understanding and applications of (multi-)ferroic perovskites.


Scope :


Perovskites’ tremendous significance in the field of functional materials originates from the versatility and flexibility of its crystal structure. Not only does the perovskite family offer various degrees of freedom for the design of materials with desired properties, but it also provides many compounds that serve as models for in-depth understanding of various physical properties and phenomena. As such, the perovskite family defines a research field in itself where tight collaboration between advanced solid state theory and experiment has proven to be particularly fruitful. Ferroic phase transitions and properties, including ferroelectricity, ferroelasticity, magnetism or ferrotoroidicity, are often at the heart of functional properties of perovskites. The complex interplay of their various order parameters (polarization, magnetism, strain, distortions of the octahedral network…) has been continuously under focus, in the search for original coupling phenomena that would lay the basis for advanced materials. More recently, the detailed study of domains boundaries as objects and functional elements has been pushed forward, for it offers perspectives for technological breakthrough in nanoeletronics (also called nano-ferronics). Caloric properties have also receive a renewed interest, as well as light-induced phenomena, in particular for photoferroelectrics, which in turn calls for a deeper theoretical understanding, by state of the art first-principle methods, of the electronic and optical properties of perovskites. This symposium aims at bringing together experimentalist and theoreticians working on perovskites from a variety of fields in solid state physics. Advances in synthesis methods, fundamental understanding, characterization techniques, integration and devices will be discussed.


Hot topics to be covered by the symposium:


  • Structural phase transitions and critical phenomena
  • Magnetoelectric and multiferroic perovskites
  • Domain boundary engineering 
  • Interfacial properties, 2D gases
  • Thin films, multilayers and heterostructures
  • Advances in ab-initio calculations and experimental methods
  • Electro/magneto/elasto-caloric effects
  • Flexoelectricity
  • Piezotronics and photo-piezotronics
  • Integration and devices
  • Light-induced phenomena
  • Defects in ferroic perovskites
  • Electronic structure and optical properties
  • Antiferroelectrics
  • Piezoelectrics and lead-free piezoelectrics
  • Relaxors and applications


Tentative list of invited speakers:


  • P. Zubko (UK), synthesis and properties of perovskites multilayers 
  • P. Paruch (Switzerland)
  • M. Gregg (Ireland)
  • P. Thomas (UK)
  • L. Bellaiche (USA)
  • K. M. Rabe (USA)
  • R. Waser (Germany)
  • N. Setter (Switzerland)
  • D. Rytz (Germany)
  • J.F. Scott (Cambridge)
  • H. Taniguchi (Japan)
  • J.-M. Triscone (Switzerland)
  • A. Barthélémy (France)
  • M. Stengel (Spain)


Tentative list of scientific committee members:


  • B. Noheda (Netherlands)
  • J. Kreisel (Luxembourg)
  • M. Alexe (UK)
  • L. Eng (Germany)
  • J. Fontcuberta (Spain)
  • B. Hilczer (Poland)
  • M. Maglione (France)
  • P. Ghosez (Belgium)
  • M. Tyunina (Finland)
  • D. Damjanovic (Switzerland)


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Lead-free ferro and piezoelectrics : H. Taniguchi
Authors : Steven Huband, Pam Thomas
Affiliations : University of Warwick

Resume : Na0.5Bi0.5TiO3 (NBT) based ceramics are promising candidates for lead-free piezoceramic devices. The (1-x-y)NBT-xBaTiO3-yK0.5Na0.5NbO3 (NBT-BT-KNN) system in particular has been shown to have a large strain comparable to lead-containing materials1. These measurements focus on a small range in the NBT-BT-KNN system between x=5 to 7 and y=1 to 3. This region contains two distinct groups in terms of properties; one group contains compositions with ferroelectric P-E loops while the other group, with higher BT and KNN content, consists of samples with pinched P-E loops. This change from ferroelectric to pinched hysteresis loops with small changes in composition can also be induced by heating2. The change from ferroelectric to pinched P-E loops has been measured in other NBT based materials as well, such as (1-x)NBT-xBa(Al0.5Ta0.5)O3 (NBT-BAT)3. We report on the results of an investigation of the structural variations in these materials and how they relate to the physical properties. At zero-applied electric field, the structure as a function of temperature has been investigated using x-ray diffraction measurements. The temperature dependence of the physical properties has been studied using measurements of P-E loops, dielectric permittivity and the second harmonic generated intensity. The results are discussed both in the context of the published work and fundamental understanding of the origin of the pinched P-E loops. References: 1 S.T. Zhang, A.B. Kounga, E. Aulbach, T. Granzow, W. Jo, H. Kleebe, and J. Rödel, J. Appl. Phys. 103, 034107 (2008). 2 S.T. Zhang, A.B. Kounga, E. Aulbach, W. Jo, T. Granzow, H. Ehrenberg, and J. Rödel, J. Appl. Phys. 103, 034108 (2008). 3 W. Bai, Y. Bian, J. Hao, B. Shen, and J. Zhai, J. Am. Ceram. Soc. 96, 246 (2013).

Authors : J. Bieker (1), H. Choe (2), M. Tolan (1), U. Pietsch (2), S. Gorfman (2)
Affiliations : (1) Department of Physics, TU Dortmund University, Dortmund, Germany (2) Department of Physics, University of Siegen, Siegen, Germany

Resume : The electromechanical coupling in perovskite-based ferroelectrics has been in focus of many studies, motivated by the interest to understand the connection between piezoelectricity and ferroelectricity and the urgent need to design environmentally friendly replacements to the dominating lead-based PbZr1-xTixO3. The promising candidates are Na0.5Bi0.5TiO3 - BaTiO3 (NBT-BT) solid solutions.The aim of this work is to probe the structural mechanisms of converse piezoelectricity in multi-domain single crystal of Na0.5Bi0.5TiO3 (NBT) - the end-member of NBT-BT. We implemented a custom-built data-acquisition system for stroboscopic time-resolved X-Ray diffraction. The system synchronizes the timings of X-ray detector signals with the periodically applied triangular electric field. We collected several {00l}pc Bragg rocking curves and analyzed the dynamic of the corresponding average c-lattice parameter as a function of time and electric field. Furthermore, we inspected the fine structure of the diffraction profiles and attempted to explain the observed changes in terms of purely intrinsic and extrinsic models of piezoelectric effect. We proved the dominance of intrinsic contributions and the presence of two electromechanically different volume fractions. One of these fractions exhibits distinct asymmetric behavior with respect to the changing polarity of electric field. This result is discussed in the framework of the recently proposed room temperature monoclinic symmetry of NBT.

Authors : hyun Ae Cha, Jae-Ho Jeon
Affiliations : Korea Institute of Materials Science (KIMS), Korea Institute of Materials Science (KIMS)

Resume : Plate-like Bi0.5Na0.5TiO3 (BNT) and Bi4.5Na0.5Ti4O15 (BNT15) are major templates for texturing of lead-free piezoelectric ceramics such as Bi0.5Na0.5TiO3-BaTiO3 (BNT-BT) and Bi0.5(Na,K)0.5TiO3 (BNKT). These templates are usually synthesized by Topochemical Microcrystal Conversion (TMC) method using a mixture of plate-like Bi4Ti3O12 (BiT), TiO2 and Na2CO3 powders. In this work, we researched the formation mechanism of BNT and BNT15 during TMC process by investigating the effect of the size of BiT/TiO2 reactants on the shape and size of BNT/BNT15 products. Plate-like BiT precursor was synthesized by a molten-salt process with size from 2 µm to 11 µm by controlling reaction temperature and duration time. We used TiO2 powders with average size of 15, 100 and 300 nm. The result showed that TMC process produced BNT powders consisting of plates and cubic particles. The size of BNT plate was dependent on the size of BiT plate, but the size of BNT cube was dependent on the size of TiO2 particle. However, in the case of BNT15 synthesis, only the plate shape was formed and the size of BNT15 plate was dependent on the size of BiT plate. Both BiT and BNT15 have layer-structure consists of alternately stacked [Bi2O2]2+ layers and pseudo-perovskite blocks, and BNT has perovskite structure. Our results indicate that both BNT and BNT15 are synthesized by the same process of solution-diffusion during TMC, but the behaviors of TiO2 particles are different during the synthesis of both phases.

Authors : Sergejus Balčiūnas, Maksim Ivanov, Jūras Banys, Satoshi Wada
Affiliations : Faculty of Physics, Vilnius University, Sauletekio 9/3 817k., LT10222 Vilnius, Lithuania; Faculty of Physics, Vilnius University, Sauletekio 9/3 817k., LT10222 Vilnius, Lithuania; Faculty of Physics, Vilnius University, Sauletekio 9/3 817k., LT10222 Vilnius, Lithuania; Interdisciplinary Graduate School of Medical and Engineering, University of Yamanashi, Kofu,Yamanashi 400-8510, Japan

Resume : Barium titanate (BT) is a classic ferroelectric with average properties. However, they can be improved in two ways – by either introduction of other ions into the lattice, or by making a composite material. Morphotropic phase boundary is the goal in the first case, but it is not always present in different combinations of materials. The second case is less demanding, but requires epitaxial interfaces between the different regions of the composite. If Potassium niobate (KN) is inserted into the BT structure and forms a composite with epitaxial interfaces, then stresses are created, that increase domain wall count and as a result piezoelectric coefficient. Although ferroelectric Pb(Zr,Ti)O3 has taken a substantial share of piezoelectric market due to its high piezoelectric characteristics, BT-KN composite ceramics have a potential to become a substitute. The fact that BT-KN is lead free ceramic makes it of high interest for both researchers and engineers due to environmental concerns. In this presentation dielectric properties of BT-KN with KN molar ratios of 0.22, 0.25 and 0.5 will be presented. It was experimentally found that there is a strong contribution of piezoelectric effect to the effective permittivity of the composites. The characteristic frequency of the process depends on mean cluster size of the barium titanate particles. Furthermore, adjacent grains have correlated direction of net polarisation of the grains.

Authors : Huazhang Zhang, Wen Chen, Jing Zhou, Jie Shen, Xiong Yang, Hui Wang
Affiliations : State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, and School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070, P. R. China

Resume : Bi1/2Na1/2TiO3 (BNT) based ceramics are currently received much attention due to their potential application as the environmental friendly alternatives if compared to that of Pb(Zr,Ti)O3 (PZT) based piezoceramics. In the binary system Bi1/2Na1/2TiO3-Bi1/2K1/2TiO3 (BNT-BKT), optimized piezoelectric properties were achieved near the morphotropic phase boundary (MPB) between rhombohedral and tetragonal phases, while the depolarization temperature (Td) was sharply decreased [1]. Recent studies suggested that piezoelectric depolarization in NBT-based materials was due to the transition from ferroelectric state to ergodic relaxor state with dynamic nanoscale polar regions, which disrupted the long-range ferroelectric order [2]. On the other hand, the stability of ferroelectric order may be tailored by doping. Davies et al. showed an increase in the Td with doping Fe in BNT [3]. Jo et al. found that Fe promotes ferroelectric stability in Bi1/2Na1/2TiO3-BaTiO3-(K0.5Na0.5)NbO3 (BNT-BT-KNN) by the formation defect dipoles [4]. Therefore, Fe doping in BNT-BKT system was expected to stabilize the ferroelectric order and improve piezoelectric property and thermal stability. In the present work, the MPB compositions 0.8Bi0.5Na0.5TiO3-0.2Bi0.5K0.5TiO3 doped with Fe were prepared via a conventional solid state route, and the effect of Fe doping on structure and electrical properties of the ceramics was investigated. All the specimens exhibited single-phase perovskite structure, and the rhombohedral-tetragonal phase coexisted. By Fe doping, the dielectric constant had almost no change, while piezoelectric properties were enhanced. Polarization-electric field hysteresis loops revealed that Fe doping served to increase the coercive field and the remnant polarization. Additionally, the thermal depoling experiment demonstrated that the depolarization temperature increased by Fe doping, which was further verified by the temperature dependent dielectric properties and polarization-electric field hysteresis loops. In conclusion, the ferroelectric order could be stabilized by Fe doping, and led to the enhanced piezoelectric coefficients and thermal stability. References: [1] Yoshii, K.; Hiruma, Y.; Nagata, H.; et al. Jpn. J. Appl. Phys., 2006, 45, 4493. [2] Jo, W.; Schaab, S.; Sapper, E.; et al. J. Appl. Phys., 2011, 110, 074106. [3] Davies, M.; Aksel, E.; Jones, J.L. J. Am. Ceram. Soc., 2011, 94, 1314. [4] Jo, W.; Erdem, E.; Eichel, R.A.; et al. J. Appl. Phys., 2010. 108, 014110.

10:30 Coffee break    
Multiferroics I : P.E. Janolin
Authors : L. Bellaiche1, S. Bhattacharjee1, X.M. Chen2, J. Iniguez3,4, A. Mao5, D. Rahmedov1, W. Ren6, D. Wang7, B. Xu1, Y. Yang1 and H. Zhao2.
Affiliations : 1Physics Department and Institute for Nanoscience and Engineering, University of Arkansas, Fayetteville, Arkansas 72701, USA 2Laboratory of Dielectric Materials, Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China 3Materials Research and Technology Department, Luxembourg Institute of Science and Technology, 5 avenue des Hauts-Fourneaux, L-4362 Esch/Alzette, Luxembourg 4Institut de Ciencia de Materials de Barcelona (ICMAB-CSIC), Campus UAB, 08193 Bellaterra (Barcelona), Spain 5Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065, China 6 Department of Physics, Shanghai University, 99 Shangda Road, Shanghai 200444, P. R. China 7Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education and International Center for Dielectric Research, Xi'an Jiaotong University, Xi'an 710049, China

Resume : Multiferroic materials have recently experienced a regain of interest because of their inherent cross coupling between electric and magnetic degrees of freedom. In particular, a systematic control of the magnitude and crystallographic direction of magnetic order parameters by an electric field is attractive for the design of original devices. The aim of this Talk is to report the results of ab-initio and first-principles-based calculations that predict two different novel ways to achieve such control in multiferroic BiFeO3 (BFO). 1) One way to attain such control is via the existence of an energy term that (i) directly couples magnetic moments and electric polarization, P, and (ii) is linear in P. A particular example of such energy term is the spin-current model [1,2,3]. Here, we demonstrate that this term allows an electric-field-driven and ultrafast switching of the magnetic chirality in the ground state of BFO (that is R3c on a structural point of view and that exhibits a cycloid on a magnetic point of view) [4]. This switching is further found to involve original intermediate magnetic states. 2) Another way to control magnetic quantities by an electric field can be thought as being ``indirect’’: there is a trilinear ``structural-only'' coupling between polarization and two different structural quantities that leads to the reversal of one of these two structural quantities when switching the direction of the polarization [5]. Then, this reversal can result in the change of direction of a magnetic order parameter, via a second physical energy [6]. Here, we show that such ``indirect’’ magneto-electric coupling can indeed exist in BFO films, and provide the analytical expression and original physical quantities of these two energies [7]. If times allows, other striking magneto-electric effects will also be discussed [8,9,10]. These works are supported by the Department of Energy, Office of Basic Energy Sciences, under contract ER-46612, ARO grant W911NF-12-1-0085, NSF grant DMR-1066158 and ONR Grants N00014-12-1-1034 and N00014-11-1-0384. Some computations were also made possible thanks to the ONR grant N00014-07-1-0825 (DURIP), the MRI grant 0722625 from NSF and a Challenge grant from the Department of Defense. References: [1] H. Katsura, N. Nagaosa, and A. V. Balatsky, Physical Review Letters 95, 057205 (2005). [2] D. Rahmedov et al, Physical Review Letters 109, 037207 (2012). [3] A. Raeliarijaona, S. Singh, H. Fu, and L. Bellaiche, Physical Review Letters 110, 137205 (2013). [4] S. Bhattacharjee et al, Physical Review Letters 112, 147601 (2014). [5] N. A. Benedek and C. J. Fennie, Physical Review Letters 106, 107204 (2011). [6] L. Bellaiche et al, Journal of Physics Condensed Matter 24, 312201(2012). [7] Y. Yang et al, Physical Review Letters 112, 057202 (2014). [8] H. J. Zhao et al, Nature Communications 5, 4021 (2014). [9] B. Xu et al, Advanced Functional Materials, DOI: 10.1002/adfm.201403811 (2014). [10] B. Xu et al, Advanced Functional Materials, DOI: 10.1002/adfm.201501113 (2015).

Authors : J.-Y. Chauleau1, S. Fusil2, C. Carretero2, M. Viret1
Affiliations : 1. Service de Physique de l’Etat Condensé, Commissariat à l’Energie Atomique, DSM/IRAMIS, UMR CNRS 3680, CEA Saclay, 91191 Gif-Sur-Yvette, France 2. Unité Mixte de Physique CNRS/Thales, 1 avenue Fresnel, 91767 Palaiseau, France

Resume : Multiferroic materials are the focus of an intense research effort due to the significant technological interest of multifunctional materials as well as the rich fundamental physics lying in the coupling of various order parameters. Among all multiferroics, BiFeO3 (BFO) is a material of choice because its two ordering temperatures (ferroelectric and antiferromagnetic) are well above room temperature. In addition a fairly large magnetoelectric coupling has been demonstrated in single crystals as well as in thin films. In this study, we investigate the possibility to use second harmonic generation (SHG) to access the sub-micron distribution of the different order parameters and visualize the magnetoelectric coupling. We clearly observe the presence of substructure patterns in ferroelectric monodomains written using a piezo-force microscope. The topology of the observed domains thus depends on the electrical writing process. We will present here detailed measurement of the symmetry of the SHG signal as well as its wavelength dependence pointing to the existence of a magnetic contribution which emerged after electrical writing.

Authors : Dashan. Shang1, Y. S. Chai1, Z. X. Cao1, J. Lu1, S. H. Chun2, K. H. Kim2, Y. Sun1
Affiliations : 1Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China. 2CeNSCMR, Department of Physics and Astronomy, Seoul National University, Seoul 151-747, South Korea

Resume : In addition to resistor, capacitor and inductor, Chua proposed in 1971 the fourth fundamental circuit element to directly relate magnetic flux and charge. Such a circuit element, dubbed memristor, was later attributed to the non-linear current-voltage characteristic and has been realized in various material structures. Here we clarify that a two-terminal device employing magnetoelectric effect possesses the function of relating directly magnetic flux and charge, and fulfill the definition of the fourth circuit element. Both the linear and the nonlinear memory devices having this function, dubbed transtor and memtranstor, respectively, are realized by sandwiching a magnetoelectric hexaferrite crystal in electrodes. Moreover, the devices can operate either in the charge-driving mode or in the flux-driving mode, and the transdance arising from the magnetoelectric coefficient can be both positive and negative, thus displaying a pinched hysteresis loop with special shape. With the introduction of transtor and memtranstor, a complete and harmonized relational graph can be constructed for the fundamental circuit variables, which will be helpful for broadening circuit functionality for next-generation intelligent devices in future.

Authors : A. Barbier(1), T. Aghavnian(1,3), V. Badjeck(1,2), C. Mocuta(3), D. Stanescu(1), H. Magnan(1), C. L. Rountree(1), R. Belkhou(3), P. Ohresser(3), N. Jedrecy(2)
Affiliations : (1) DSM/IRAMIS/SPEC, CNRS URA 2464, CEA Saclay, F-91191 Gif-sur-Yvette, France (2) Sorbonne Universités, UPMC Paris 06, UMR 7588, INSP, 4 Place Jussieu, F-75005 Paris, France (3) Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin, F-91192 Gif-sur-Yvette Cedex, France,

Resume : Doping ferroelectric compounds to produce novel multiferroic materials is a seductive approach. We report on the Fe doping and on the comparative NiFe2 co-doping of fully oxidized BaTiO3 layers (~ 20 nm) elaborated by atomic oxygen plasma assisted molecular beam epitaxy. The films were thoroughly characterized by synchrotron radiation X-Ray diffraction and X-Ray absorption spectroscopy. For purely Fe doped layers, the native tetragonal perovskite structure evolves rapidly towards cubic-like up to 5% doping level above which the crystalline order disappears. On the contrary, low co-doping levels (~5%) fairly improve the thin film crystalline structure and surface smoothness; high levels (~27%) lead to more crystallographically disordered films, although the tetragonal structure is preserved. Magnetic dichroic measurements reveal that metal clustering does not occur and allowed determining the ion valences. Ferromagnetic long range ordering can be excluded with great sensitivity in all samples as deduced from X-Ray magnetic absorption circular dichroic measurements. On the contrary, our linear dichroic X-Ray absorption results support antiferromagnetic long range ordering while piezo-force microscopy give evidence of a robust ferroelectric long range ordering showing that the films are excellent candidates for magnetic exchange coupled multiferroic applications.

Authors : B. Dabrowski1, O. Chmaissem1, S. Kolesnik1, V. Goian2, S. Kamba2
Affiliations : 1Deptment of Physics, Northern Illinois University, DeKalb, IL, USA; 2Institute of Physics, Academy of Sciences of the Czech Republic

Resume : It has been recently proposed that it should be possible to introduce ferromagnetism and ferroelectricity in SrMnO3-related perovskites when large strains are achieved. We have predicted earlier that similar to the d0 titanates such strain should be observed in the non-d0 perovskites resulting in a strong ferroelectric-magnetic coupling of the same magnetic ion. By advancing elaborate synthesis processes, which are necessary to avoid the more stable hexagonal polymorphs, we were recently able to extended the substitution limit of the large size Ba ion to prepare highly strained multiferroic Sr2+1-xBa2+xMn4+O3 perovskite ceramics (x=0.4-0.45) for which ferroelectricity (TF~300-350 K) and antiferromagnetism (TN~200 K) originate exclusively from the Mn (d3) cations. Similar to Ba2+Ti4+O3, the classical displacive-type ferroelectric phase transition occurs when the Mn ions move out of the center of the MnO6 octahedral units. The largest known magneto-electric coupling was observed near TN when ferroelectricity disappears. Substitution of Ti for Mn enhances ferroelectricity and increases TF to above 400 K while suppresses antiferromagnetism and lowers TN to below 200 K. As a result it is possible to tune the magnetoelectric coupling and preserve the ferroelectric phase below TF; i.e., to achieve unique displacive-type multiferroic with large spontaneous polarization.

12:30 Lunch break    
Ferroelectrics and light : B. Hehlen
Authors : J. Even, L. Pedesseau, M. Kepenekian, D. Sapori, A. Rolland, C. Katan
Affiliations : Universite Europeenne de Bretagne, INSA, FOTON, UMR CNRS 6082, 20 Avenue des Buttes de Coesmes, F-35708 Rennes, France; Institut des sciences chimiques de Rennes, CNRS – Universite de Rennes 1, UMR6226, 35042 Rennes, France

Resume : 3D hybrid perovskites (HOP) are currently superstar materials for photovoltaics and attract increasing attention of the scientific community. Recently, they also revealed attractive photoluminescence, as it is already well known for 2D layered HOP. Our modelling approach is based on concepts of solid-state physics originally developed for conventional semiconductors and nanostructures, mixing both DFT and empirical modelling. The broad light-harvesting abilities and attractive transport properties of 3D HOP can be related to the multi-bandgap and multi-valley nature of their band structure. Giant spin-orbit coupling in the conduction band is a specific property of this new class of semiconductors. Perturbations related to lattice distortion and loss of inversion symmetry at low temperature, are studied. Concept of Wannier exciton is reviewed for both 3D and 2D layered HOP. A novel approach for dielectric confinement will be described. Concepts of quantum confinement and applicability of effective masses coupled to envelope functions are analyzed for 3D heterostructures and 2D layered HOP.

Authors : Ugur Unal
Affiliations : Koc University Chemistry Department Surface Science and Technology Center Rumelifeneri yolu Sariyer 34450 Istanbul Turkey

Resume : Photoluminescent layered oxides doped with lanthanides are always attracted to scientific community. Layered oxide materials are important because of their physical and chemical stabilities and also with the photoluminescence of lanthanides with well-defined 4f transitions in the host layer. There are many examples of photoluminescent lanthanide doped oxide materials. These materials are generally 3D bulk crystals or amorphous materials. Layered oxides are unique with their layered structure and have distinctive properties. Layered oxides can be exfoliated into their 2D nanosheets. These nanosheets can absorb light efficiently because of their planar surface and high aspect ratio. Ultra thin films can be deposited in a controlled manner by using these nanosheets. Different classes of nanosheets doped with different lanthanide cations can be utilized in order to fabricate thin composite films emitting light at different wavelengths. Layered perovskite oxides are intergrowths of perovskite and other structures. They consists of two-dimensional perovskite sheets separated with cations or cationic units. They are classified as Dion-Jacobson, Ruddlesden-Popper and Aurivillius phases. The A site in the perovskite layer can be exchanged with another cation which could be s-, p- or f- block cation. In general, f-group cations will be emission centers and perovskite will emit at characteristic wavelengths of the f-block element as a result of well-defined f-f transition. Nanosheets doped with f-block elements can easily be prepared from bulk layered oxides by using wet-chemistry. I will discuss the optical properties of lanthanide doped Aurivillius and Dion-Jacobson phase layered perovskite materials. Harmonic oscillation and upconversion examples of these type of layered oxides doped with lanthanides will be presented. I will also show some examples of photocatalytic properties of perovskite type layered oxides. We would like to acknowledge TUBITAK for funding through project 114Z452 (Synthesis of two dimensional luminescent perovskite nanosheets).

Authors : X. F. Bai [1], N. Banja [1], J. Wei [1,2], P. Gemeiner [1], N. Guiblin [1], R. Haumont [3], B. Dkhil [1], D. Lenoble [4], and I. C. Infante [1]
Affiliations : [1] SPMS Lab. UMR8580 CNRS & CentraleSupélec, Université Paris-Saclay, Grande voie des vignes, 92295 Chatenay-Malabry, France; [2] Electronic Materials Research Lab., Key Laboratory of Ministry of Education, Xi’an Jiaotong University, Xian Ning West Road No.28, 710049 Xi’an, China; [3] Laboratoire de Physico-Chimie de l'Etat Solide ICMMO UMR8182 CNRS, Université Paris Sud XI, Bât. 410, 15 rue Georges Clémenceau, 91405 Orsay, France; [4] Luxembourg Institute of Science and Technology LIST, 41 rue du Brill, 4422 Belvaux, Luxembourg

Resume : Recently, ferroelectric perovskites like have received a lot of attention though presenting, added to their ferroelectric properties, new interesting photoinduced or photoferroelectric properties (photovoltaicity, photostriction, photocatalysis) observed in the visible range. Our work presented here is devoted to the investigation for their potential application by considering several photoferroelectric materials based on BiFeO3 and BaTiO3 compounds. Through studying the doping effects and different solid solutions involving other insulating perovskites, we will show results on micro/nanopowders and ceramics that prove the possibility to tune not only the structure and the ferroelectric order of these systems, but also the optical and electronic band gap. Our first results on photocatalytic properties of these systems will be analyzed within the framework of the corresponding effect of particle size, surface termination and doping. Perspectives on future applications of photoferroelectric-based materials for visible light photocatalysis will be presented.

Authors : Mads Weber (1,2), Mael Guennou (1), Constance Toulouse (3), Maximilien Cazayous (3), Yannick Gillet (4), Xavier Gonze (4), Jens Kreisel (1,2)
Affiliations : 1 Luxembourg Institute of Science and Technology, 2 University of Luxembourg, 3 LMPQ, Université Paris Diderot-Paris 7, 4 Université Catholique de Louvain

Resume : Knowledge of the electronic band structure of materials is a cornerstone of modern technology. In functional dielectric and multiferroic oxides, traditionally seen and used as insulating materials, electronic structures have been much less explored than in semiconductors. However, today, they gain importance with the growing interest for interactions of ferroic materials with light, namely in the view of photovoltaic or photoelectric properties. Here, we show how resonant Raman spectroscopy enables to probe electronic levels of the model multiferroic BiFeO3 (BFO). Using twelve different excitation wavelengths ranging from the deep blue (442 nm = 2.8 eV) to the infrared (785 nm = 1.6 eV), we show that both the first- and second-order Raman signatures of the crystals differ significantly for different laser wavelengths. Careful analysis of the intensities allows the discussion of oxygen electronic defect levels and both the direct and indirect band-gaps. Notably, temperature-dependent experiments provide the first experimental indication that the reported strong variations of the optical band-gap in BFO originates from a decreasing indirect electronic gap. More generally, our study suggests that Raman scattering at various wavelengths offers a well-adapted probe for the investigation of electronic excitations in multiferroic functional oxides.

Authors : S. Nadupalli, T. Granzow
Affiliations : Luxembourg institute of science and technology (LIST)

Resume : One of the most fundamental aspects of photo-ferroelectric behaviour is the light-induced charge transport. In this context, it is essential to take into account the bulk photovoltaic effect (BPVE). Unlike normal photovoltaic effect in semiconductors that rely on the separation of charge carriers at p-n-junctions where voltage created can never exceed the band gap energy, the BPVE scales with sample thickness and can create an arbitrarily high voltage. There are several competing propositions for the mechanism driving the charge carriers. For Fe:LiNbO3, the most prominent material with a large BPVE, a recent model [1] is based on the transition of the electron from an Fe-donor to a small free Nb polaron state with the transition probability depending on interatomic distances. Both interatomic distances and phonon spectrum are susceptible to mechanical stress. This presentation will elucidate the origin of the BPVE by determining the short-circuit current of LiNbO3:Fe at different levels of uniaxial compressive stress under homogeneous illumination. The full stress-dependence of the BPVE is quantified via the piezo-photovoltaic tensor. The stress-dependence of the phonon spectrum is determined by Raman spectroscopy and the changes in interatomic distances by structural characterization. The results are discussed based on predictions made from the theory proposed by Schirmer et al.. [1] O. Schirmer et al., Phys. Rev. B 83, 165106 (2011).

Authors : D. Gryaznov(1), M. Arrigoni(2), E. A. Kotomin(1,2), A. Popov(1)
Affiliations : (1) Institute of Solid State Physics, University of Latvia, Riga, Latvia (2) Max Planck Institute for Solid State Research, Stuttgart, Germany

Resume : Oxygen vacancies in ABO3 type perovskites play an important role for many applications. Using hybrid DFT calculations combined with LCAO basis set and periodic supercell approach, the atomic, electronic structure, and phonon properties of both neutral and fully charged oxygen vacancies in several perovskite oxides (SrTiO3, LaFeO3, LaCoO3 and BaZrO3) were calculated and compared. An emphasis is given to the analysis on the role of 3d-electrons in determining the system electronic structure and the presence of so-called “ghost” basis functions centered at the vacant site. It is shown that the Gibbs free formation energy (Gf) of neutral oxygen vacancy is smaller when a basis set is present at the vacant site than without the basis functions. The electronic charge concentrated within a neutral vacancy varies from 0.5 e (SrTiO3) to almost 1.0 e (BaZrO3), indicating a considerable effect of the electron localization and depending on the position of defect level in the band gap. Also, the contribution of phonons to Gf in BaZrO3 is shown to be much larger for the charged vacancy in a comparison with the neutral vacancy whereas it is still large for the neutral vacancy in SrTiO3 due to the temperature dependence of soft modes. We present a careful comparison of the obtained results with the experimental data for the optical properties, electrical conductivity and thermogravimetry measurements.

15:30 Coffee break    
Multiferroics II : B. Dkhil
Authors : N. A. Pertsev
Affiliations : Ioffe Institute and Peter the Great St. Petersburg Polytechnic University, St. Petersburg, Russia

Resume : In this invited talk, we discuss dynamic magnetoelectric effects in multiferroic heterostructures comprising ferromagnetic nanolayers interfacially coupled to ferroelectric perovskites. In such heterostructures, the interfacial magnetic anisotropy depends on the ferroelectric polarization so that the magnetization precession and switching can be induced electrically by a voltage applied to the ferroelectric component. First, we describe non-180-degrees magnetization reorientations in ferromagnetic nanolayers driven by the polarization switching in adjacent ferroelectric. Importantly, these polarization-controlled reorientations may lead to significant resistance switching in multiferroic tunnel junctions (MFTJs), where an ultrathin ferroelectric barrier is embedded between ferromagnetic electrodes. Using Fe/BaTiO3/Fe junctions as a representative example, we demonstrate that such MFTJs can be employed as electric-write memory cells. Next, we describe magnetization oscillations excited by an ac voltage applied to the heterostructure. Since ferroelectric perovskites have much higher permittivities than conventional dielectrics, much smaller voltages may be employed for the generation of similar oscillations. Finally, we analyze the influence of polarization-dependent interfacial anisotropy on the magnetization reversal driven by spin-polarized currents and compare critical current densities predicted for MFTJs with those characteristic of MgO-based magnetic tunnel junctions.

Authors : M. Viret1, J.-Y Chauleau1, M. Goirant2, B. Raquet2, J. Tranchida3 and P. Thibaudeau3
Affiliations : 1. Service de Physique de l’Etat Condensé, Commissariat à l’Energie Atomique, DSM/IRAMIS, UMR CNRS 3680, CEA Saclay, 91191 Gif-Sur-Yvette, France 2. Laboratoire National des Champs Magnétiques Intenses, Toulouse, France 3. Commissariat à l’Energie Atomique, CEA/DAM Le Ripault, 37260 Monts, France

Resume : BiFeO3 is the only (antiferro)magnetic ferroelectric at room-temperature, which makes this material a strong candidate for any potential application. The magneto-electric effect links the electric and the magnetic states of BiFeO3 which could be used to address a magnetization with an electric field. On the other hand, because BiFeO3 is essentially an antiferromagnet, it is rather insensitive to an applied magnetic field. However, the magnetoelectric coupling effect is responsible for the establishment of a long period cycloidal arrangement, which can be affected by the application of a large magnetic field. Indeed, above around 19T the Zeeman energy dominates and the cycloid gets unstable and is replaced by a global canting. The destruction of the cycloidal structure releases the electrical charges due to the magnetoelectric interaction. The detailed study of this effect as a function of the direction of a high magnetic field relative to the spin rotation plane gives interesting information of the magnetoelectric properties of the cycloidal arrangement. Micromagnetic simulations have also been performed in order to better understand the magnetic field effect and the magnetoelectric coupling. It appears that some features may be explained by the specific role of antiferromagnetic domain walls. These interesting entities will be discussed in the light of the local magnetoelectric coupling.

Authors : G. Drera (1), A. Giampietri (1), I. Alessandri (2), E. Magnano (3), F. Bondino (3), S. Nappini (3), L. Sangaletti (1)
Affiliations : 1 - Interdisciplinary Laboratories for Advanced Materials Physics (I-LAMP), Università Cattolica del Sacro Cuore, Brescia, Italy; 2 - NSTM and Chemistry for Technologies Laboratory, Mechanical and Industrial Engineering Department (DIMI), University of Brescia, Brescia, Italy; 3 - IOM-CNR, Laboratorio TASC, S.S. 14, Km 163,5 I-34149 Basovizza, Italy.

Resume : Multiferroic materials, which simultaneously display ferroelectricity, ferromagnetism (or antiferromagnetism) and ferroelasticity, have already attracted much attention due to the promising multifunctional device applications. Bismuth ferrite (BiFeO3, BFO in short) is the only room-temperature single-phase multiferroic, with high ferroelectric Curie temperature (1103 K) and Neel temperature (643 K). Polycrystalline BFO can be easily obtained by sputtering, which represent a fast, cheap and reproducible method for industrial applications. However, for oxide-based spintronics and electronics, epitaxial thin films are required, with large and uniform multiferroic domains. Under this condition, epitaxial films may exhibit new interface properties (such as in the popular LaAlO3-SrTiO3 system) which in multiferroics can be driven by tuning the overlayer polarization. In this work, we show the characterization of polycrystalline and epitaxial BFO thin films grown on Si and TiO2-terminated SrTiO3 (STO) substrates by RF sputtering, carried out with a large set of spectroscopic and microscopic techniques (XPS,micro-Raman,XRD,AFM/PFM) for various growth temperatures and post-growth treatments. On the Si substrate, polycristalline BFO films with tunable grain size are obtained, while on the oriented STO a transition from amorphous to epitaxial growth is identified through the appearance of X-ray photoelectron diffraction modulations in the angle-resolved XPS spectra.

Authors : Charles Paillard [1], Gregory Geneste [2], Brahim Dkhil [1]
Affiliations : [1] Laboratoire SPMS, UMR 8580, CentraleSupélec, CNRS, Université Paris-Saclay, Grande Voie des Vignes 92 295 Châtenay-Malabry CEDEX, France; [2] CEA, DAM, DIF, F-91297 Arpajon France

Resume : There is an increasing interest in the investigation of defects formation and properties in multiferroics, as they are believed to play a key role in enhancing transport properties [1,2] (to the point of superconductivity in WO3 [3]), or creating new complex distribution of the magnetic/electric degrees of freedom (e.g. vortices [4]). The impact of defects on pinning domain walls [5,6], fatigue and imprint, remains to be exhaustively studied in order to understand how defects can deteriorate/enhance material functionalities. We studied the occurrence of single and bi-defects in Bismuth Ferrite using ab-initio calculation with ABINIT, both in GGA and LDA+U, and show that the necessary corrections to achieve the study of defects in the dilute limit yield similar results. In addition, we show that single point defects will tend to aggregate, with a binding energy for the Bi-O pair of approximately 0.15 eV. Finally, we study the possibility to engineer defects by using different atmospheres in oxygen. Acknowledgements References [1] S. Farokhipoor, B. Noheda, Phys. Rev. Lett. 107, 127601, (2011). [2] J. Seidel, L. Martin, Q. He et al., Nat. Mat. 8, 229, (2009). [3] E. Salje, Chem Phys Chem 11, 940, (2010). [4] D. Viehland and E. Salje, Adv. Phys. 63, 267, (2014). [5] L. He and D. Vanderbilt, Phys. Rev. B 68, 134103 (2003) [6] A. Chandrasekaran et al., Phys. Rev. B 88, 214116 (2013)

Poster session : M. Guennou
Authors : А. V. Pashchenko 1, V. P. Pashchenko 1, †, V. K. Prokopenko 1, Yu. F. Revenko 1, А. S. Мazur 1, V. А. Тurchenko 1,2, V. V. Burchovetski 1, V. Ya. Sycheva 1, M. O. Liedienov 1
Affiliations : 1 Donetsk Institute for Physics and Engineering named after O. O. Galkin NASU, 03680, Kyiv, Ukraine; 2 Joint Institute for Nuclear Researches, 141980, Dubna, Russia

Resume : Rare-earth bismuth-containing manganites with a perovskite structure relate to the perspective multifunctional materials of spintronics. In these materials the polarization effects of magnetical and ferroelectric states manifested in the coexistence of magnetoresistance (MR) and ferroelectric (FE) properties are observed. The possibility of focused changes and management of these properties due to changes in the composition, structure and its defects determines the relevance of the research. Single-phase ceramics La0.6Sr0.3-xBixMn1.1O3-δ (x=0;0.1;0.15;0.2) obtained by the standard solid-state reaction was investigated by X-ray, thermogravimetric, resistive ρ, magnetic, 55Mn NMR, SEM and MR methods. The substitution of Sr2+ ions by bismuth leads to an increase in the parameter of the R3 ̅c perovskite structure, low temperatures of “metal-semiconductor” and “ferro-paramagnetic” phase transitions, as well as reducing peak temperature of MR-effect. The part of bismuth ions are in the B-position as Bi5+. The increase of the activation energy and a sharp increase in ρ indicate the approach of a FE-state. Defective molecular formulas of the real perovskite structure containing anion and cation vacancies were determined. The analysis of 55Mn NMR spectra confirmed the conclusion about the manganese ions environment heterogeneity by vacancy-type defects. The constructed phase diagram shows a strong correlation between the defect structure and the properties of ceramics investigated.

Authors : Min-Soo Kim, Jong-Gyeon Ahn, Soon-Jong Jeong, In-Sung Kim, Jaesung Song
Affiliations : Battery Research Center, Korea Electrotechnology Research Institute, Changwon, Rep. of Korea

Resume : (Na,K)NbO3 based ceramics are known to be harmless and promising candidates for replacing Pb(Zr,Ti)O3 ceramics because of their potential piezoelectric properties. However, it is difficult to sinter the ceramics via conventional sintering process. In this study, it was investigated that the effect of additions with A-site ions in perovskite structure on electromechanical properties and grain growth behaviors in (Na0.475K0.475Li0.05)(Nb0.95Ta0.05)O3 (NKLNT) ceramics. Sintering temperature was lowered by adding A-site ions and abnormal grain growth in NKLNT ceramics was observed with varying additions. This grain growth behavior was explained in terms of interface reaction-controlled nucleation and growth. The piezoelectric properties of NKLNT ceramics were investigated as a function of concentration of additions. The electromechanical coupling factor and piezoelectric constant were improved in the samples with A-site ions excess NKLNT. These results show that the electromechanical properties of NKLNT ceramics can be improved by controlling the microstructures.

Authors : Jakub Kaczkowski
Affiliations : Institute of Molecular Physics Polish Academy of Sciences, ul. M. Smoluchowskiego 17, 60-179 Poznań, Poland

Resume : The first-principles total energy calculations of BiAlO3 and BiGaO3 in different crystal phases under pressure up to 15 GPa have been performed within generalized gradient approximation (GGA). The calculations were done within projector-augmented wave method as implemented in VASP. At 10 GPa BiAlO3 undergoes a structural phase transition from rhombohedral R3c phase to orthorhombic Pnma phase. This phase transition is from ferroelectric to paraelectric phase. The calculated spontaneous polarization of rhombohedral BiAlO3 is 75 μC/cm2. In case of BiGaO3 the structural phase transition appears at 3.5 GPa from pyroxene-like structure (Pcca space group) to perovskite-like structure (Cm space group). The latter is paraelectric-ferroelectric phase transition. The calculated spontaneous polarization of BiGaO3 Cm phase is 130 μC/cm2. This work was supported by the National Science Centre (Poland) through the Grant no DEC-2011/01/B/ST3/02212.

Authors : L.E. Coy1,2, P. Graczyk2,3, C. Coll4, J.M. Bassas5, L. Rodriguez1, S. Mielcarek3, J. Ventura1, C. Ferrater1, M.C Polo1, S. Estrade4, F. Peiro4, B. Mroz 2,3, M. Varela1
Affiliations : 1. Departament Fisica Aplicada i Optica, Universitat de Barcelona, Marti i Franques 1, 08028 Barcelona, Spain; 2. NanoBioMedical Centre, Adam Mickiewicz University, Umultowska 85, 61-614 Poznan, Poland; 3. Faculty of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Poznan, Poland; 4. LENS-MIND/IN2UB, Dept. d’Electronica, Universitat de Barcelona, Marti Franques 1, 08028 Barcelona, Spain; 5. Serveis Cientificotecnics, Universitat de Barcelona, 08028 Barcelona, Spain;

Resume : Barium titanate and bismuth ferrite are the most extensively studied multiferroic materials. They are of high interest mainly due to simple perovskite crystallographic structure and possibilities of applications in non-volatile magnetoelectric devices. Nevertheless, ferroelastic properties of these crystals cannot be easily exploitable, because the reversal of electric polarization by electric field is not accompanied by a change of spontaneous strain. The strain-mediated magnetoelectric coupling is reached in this structures usually via piezoelectricity. On the other hand, ferroelasticity in Gd2(MoO4)3 (gadolinium molybdate) could be exploited more easily, since it is a full ferroelectric- full ferroelastic crystal. Hence, the reversal of polarization by electric field induces change in spontaneous strain there. The permanent spontaneous strain will stabilize magnetic information in multiferroic heterostructures more effectively. Here we report on the first study devoted to the thin film stabilization of GMO and the study of its epitaxial relationship on strontium titanate (SrTiO3) and silicon (001) substrates. We studied the influence of substrate temperature on the crystalline properties of the films. Morphology and epitaxial relationship were characterized with XRD, XRR, HR-TEM and AFM techniques. Results show that epitaxial strain provided by the STO(001) substrate induces the stabilization of a highly oriented Scheelite-type structure GdMoO4(001), while Si(001) allows the growth of Gd2(MoO4)3 in polycrystalline manner.

Authors : L.E. Coy1,2, L. Yate3, K. Załęski2, L. Rodriguez1, J. Ventura1,C. Ferrater1, M.C Polo1, M. Varela1
Affiliations : 1. Departament Fisica Aplicada i Optica, Universitat de Barcelona, Marti i Franques 1, 08028 Barcelona, Spain; 2. NanoBioMedical Centre, Adam Mickiewicz University, Umultowska 85, 61-614 Poznan, Poland; 3. CIC biomaGUNE, Paseo Miramon 182, 20009, San Sebastian, Spain;

Resume : A comparative study of ferromagnetic double perovskites of R(Ni0.5Mn0.5)O3 (R=Sm, Nd, Pr, La, Bi & Y) is presented. Films were carefully deposited by PLD on STO(001) substrates, aiming to stabilize a fully textured and high quality films. The epitaxial, cube on cube, single phase stabilization of the Gd & Nd perovskites was achieved, however, in the case of Sm and Y, the single phase stabilization of the films showed to be challenging. We compared both the ionic radius of the Re atoms and the lattice constants of all the RNMO perovskites, both in bulk and thin films. As a result it was shown that RNMO structure presents a limit in which the tetragonality can be induced in the unit cell, thus allowing a cube on cube epitaxial growth with different levels of epitaxial strain. The comparison of the ratio between lattice constants in the perovskites shows a critical value of b/a= 1.025 above which, the studied materials start showing multiple in-plane and out-of-plane orientations, for Ytrium and Samarium respectively. Finally, magnetic measurements and atomic force micrographs of the deposited films are shown.

Authors : T.H. Chung, X. Wu,K.W. kwok,
Affiliations : Department of Applied Physics, The Hong Kong Polytechnic University

Resume : The fabrication of co-fired multilayer piezoelectric devices is commonly used metals as the internal electrodes such as Ag and Cu. However, if the sintering temperature is higher than 1000˚C, these electrodes cannot be used due to the melting temperature. Low temperature sintering is important for multilayer piezoelectric devices. Besides, decreasing sintering temperature would also result in reduction the energy consumption and generating less pollution to the environment. However, it is hard to reduce the sintering temperature and maintain the original piezo-/ferro-/dielectric properties. Hence, it is important to choose an appropriate sintering aid to balance the sintering temperature and properties. Sintering aid can provide a liquid phase medium to increase the diffusion rate under a relatively low temperature. Low temperature sintering of 0.93(Bi0.5Na0.5TiO3)-0.07BaTiO3 (abbreviated as BNTBT) piezoelectric material with the use of Li2CO3 (x wt%) as a sintering aid was studied (BNTBT- Li2CO3-x, x = 0, 0.25, 0.5, 1, 1.5, 2). The sintering aid can improve the sinterability of the ceramics due to the effect of Li2CO3 liquid phase. The microstructure of the ceramics, together with the dielectric, ferroelectric and piezoelectric properties were investigated. The optimized Li2CO3 content was 0.5 wt%. The ceramics were sintered at 960˚C for 8 hours and exhibit piezoelectric coefficient of 183pC/N with a Curie temperature around 240˚C. The dielectric constant and dielectric loss were found to be 1570 and 5.0%, respectively. It was found that certain amount of Li2CO3 (x ≤ 0.5) can effectively reduce the sintering temperature from 1200˚C (BNTBT) to 960˚C (BNTBT- Li2CO3-0.5) with slightly decrease of the piezoelectric properties (d33), d33 would drop significantly when x ≥ 0.5 was added. Apart from the reduction of sintering temperature, the remnant polarization was also improved from 3.8 μC/cm2 to 7.6 μC/cm2 after introducing sintering aid( x = 0.5). As a result, the BNTBT- Li2CO3-x ceramics are the promising lead-free piezoelectric material and can be applied in multilayer piezoelectric devices.

Authors : H. W. Kunert1, Padmanabha Pillai K.1, M. Govender2
Affiliations : 1Department of Physics, University of Pretoria, Pretoria 0002, South Africa, 2DST/CSIR-National Centre for Nano-Structured Materials, P. O. Box 395, Pretoria, 0001, South Africa

Resume : Based on Landau-Lifshitz-Lyubarskii and our modified theory on phase transitions, the lower symmetry phases after transitions from the perovskite structure have been calculated. Our modification lies in expanding the thermodynamic potentials up to the seventh-degree, and we consider the six-fold degenerate phonons that may cause transitions. All possible lower symmetries of the perovskite crystal after transition that are induced by a specific symmetry of phonons (active irreducible representations) are given here. Our theoretical predictions are in good agreement with experimental data.

Authors : H. W. Kunert1, Padmanabha Pillai K.1, M. Govender2
Affiliations : 1Department of Physics, University of Pretoria, 0002 Pretoria, South Africa, 2DST/CSIR-National Centre for Nano-Structured Materials, P.O. Box 395, Pretoria, 0001, South Africa

Resume : The group theoretical assignments of electronic band structure of cubic perovskites have been carried out here. Using the assignments, the optical selection rules for direct and indirect optical transitions are discussed. For the indirect transitions, the symmetries of the participating phonons have been analyzed. Our theoretical results are in a good agreement with available experimental data.

Authors : H.W.Kunert1, Padmanabha Pillai K.1, M.Govender2
Affiliations : 1Department of Physics, University of Pretoria, 0002 Pretoria, South Africa, 2DST/CSIR-National Centre for Nano-Structured Materials, 0001 Pretoria, South Africa

Resume : Based on our group-theoretical assignments of the phonon dispersion curve, we have determined multi-phonon processes such as overtones, combinations, second, third and higher order interactions in CuInSe2 and CuGaGe2 and many other chalcogenides solar cell compounds of D_2d^12 symmetry. Our theoretical predictions are in good agreement with the available experimental data.

Authors : H.W.Kunert
Affiliations : Department of Physics, University of Pretoria, 0002 Pretoria, South Africa

Resume : We report on optical transitions in CuInSe2 and CuGaSe2, and many others thin film materials for photovoltaics devices of D2d 12 symmetry. Based on our group theoretical assignments of electronic band structure of solar cell compounds and thin film materials for photovoltaics we have investigated selection rules for optical transitions using infrared and Raman spectroscopies. Some of our results are confirmed by the available experimental data.

Authors : Li Chen, Man-Chung Wong, Jianhua Hao
Affiliations : (1) Department of Applied Physics, Hong Kong Polytechnic University (2) The Hong Kong Polytechnic University Shenzhen Research Institute, Shenzhen 518057, China

Resume : The development of energy harvesting white light sources converted from piezo-phototronics effect requires the search of new types of phosphors and devices. In this work, we have proposed a practical approach to design and fabricate a novel piezo-phototronics luminescence device which is made of flexible phosphor composites of doped-ZnS/polydimethylsiloxane (PDMS) coated on the top of piezoelectric Pb(Mg1/3Nb2/3)O3-xPbTiO3(PMN�PT) substrate. In the presence of an external alternating electric field, the piezoelectric actuator of PMN-PT is capable of delivering strain to the flexible phosphor composite layer and stimuli brightness white light emission. The luminescence spectra and their relations with color properties (color coordinates, color temperature, luminous efficacy, etc.) of the white light emission have been investigated. Interestingly, the achieved white light-emissions of the hybrid device can be modulated in real-time and dynamical manners under the control of low electric field. Our results show promising applications in the fields of novel white light source, energy harvesting and self-powered illumination system.

Authors : E.Yakushkin
Affiliations : Institute of Crystallography of the Russian Academy of Science, 119333, Moscow, Russia

Resume : The heat capacity in BaTiO3 single crystals was investigated in relation of domain structure peculiarities. In particular, the heat capacity was investigated at conditions of adsorption and dissociation of H2O by sample surface with different domain configurations. It was shown that the observable thermodynamic behavior of BaTiO3 single crystal strongly depends on the particular domain configurations. It was shown the great influence of water vapor adsorbed mainly by a-domains. The thermal properties were studied by the so-called ac-calorimetric method with the domain structure controlled by polarized optics. The carried out investigations provide apparently the first clear experimental evidence for the contribution of domain walls to the heat capacity measurements of the BaTiO3 single crystal. The provided results shows how in fact the domain structure may affect the thermodynamic properties of the BaTiO3 single crystal that is important for comparison to the theoretical considerations and may be useful for the domain engineering activity.

Authors : A. Jezierski ,J. Kaczkowski
Affiliations : Institute of Molecular Physics, Polish Academy of Sciences, M. Smoluchowskiego 17, 60-179 Poznań, Poland

Resume : The electronic density of states and the band structure of Pb2PtO4 (orthorhombic, space group Pbam) and PbPt2O4 (triclinic, space group P-1) is calculated by ab-initio FPLO and VASP methods. The thermodynamic properties were obtained in quasiharmonic Debye – Grüneisen approximation using GIBBS2 code. We have reported the dependence of bulk modulus, Debye temperature and specific heat on pressure and temperature. The electrical properties evolute from semiconductor (Pb2PtO4 ) to metal behavior(PbPt2O4). The calculated gap in GGA+U (UPt =3.0 eV) approximation for Pb2PtO4 is estimated as 1.02 eV at Γ point and 1.40 eV at R point. This work was funded by the National Science Centre ( NCN) grant DEC-2011/01/B/ST3/02212

Authors : SAAD BINOMRAN, Igor Kornev, Laurent Bellaiche
Affiliations : 1King Saud University, Department of Physics and Astronomy, P.O.BOX: 2455, Riyadh 11451, Saudi Arabia; Laboratoire SPMS, UMR 8580 du CNRS, Ecole Centrale Paris, 92295 Chatenay-Malabry, France; Institute for Nanoscience and Engineering and Physics Department, University of Arkansas, Fayetteville, Arkansas 72701, USA

Resume : First-principles-based scheme within the Wang-Landau algorithm is performed to provide new insights into phase transitions in ferroelectric nanodots. We decide to focus on nanodots made of (Ba0.5Sr0.5)TiO3 (BST) solid solution due to their compositionally-controllable Curie temperature and remarkable properties such as high dielectric constant, low leakage current, high pyroelectric coefficient and high dielectric breakdown voltage. Our results indicate that stress-free BST dot under short-circuit (SC) electrical boundary conditions has different phase transition behaviors than stress-free BST bulk, where three phase transitions from paraelectric-to-tetragonal, tetragonal-to-orthorhombic, and orthorhombic-to-rhombohedral exist. This indicates that the sequence of the phase transitions can change when going from bulk to low-dimensional systems. Moreover, all the phase transitions occurring in the stress-free BST nanodot are of second order. Interestingly, this is in contrast with the case of BaTiO3 bulk, which adopts a first-order paraelectric-to-ferroelectric transition. This result thus indicates that reducing the dimensionality of a system from 3D (bulk) to 0D (nanodot) can change the order of phase transition. Also, we will show the ferroelectric properties of the same system under perfect OC conditions for which the depolarizing field has its maximum value.This work is supported by the National Plan for Science, Technology and Innovation under the research project No. NANO-673-2.

Authors : Xiong Yang, Jing Zhou, Yan Xie, Jie Shen, Wen Chen
Affiliations : State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, School of Materials Science and Engineering, Wuhan University of Technology

Resume : Piezoelectric fiber composites (PFCs), such as macro fiber composites (MFCs) and active fiber composites (AFCs), have attracted increasing interest in a wide range of intellectual applications in aerospace due to their unique flexibility, adaptability, and excellent actuation performance [1, 2]. In general, a piezoelectric actuator with MFCs should be able to work under changing electrical environment such as driving voltage amplitude and frequency [3]. Further research is needed to evaluate the strain behavior and actuation performances of MFCs with the variation of driving voltage amplitudes and frequencies. In the present work, PMnS-PZN-PZT based macro fiber composites with interdigitated electrodes (IDEs) were manufactured. The effects of driving voltage amplitude and frequency on actuation behavior for polarized and unpolarized samples were also investigated, respectively. The results demonstrate that the actuation performance is strongly dependent on driving voltage amplitudes and frequencies. For initially unpolarized samples, the maximum values of strain decrease with increasing driving voltage frequencies. And the typical butterfly shape of strain loops for MFCs begins to disappear when the frequencies exceed 2 Hz. For the polarized samples, the strain and effective piezoelectric coefficients d33 increase linearly with increasing bipolar driving voltage amplitudes. And the strain loops gradually become asymmetric butterfly shape when voltage amplitudes near coercive voltage of 0.5 kV. The effective d33 values decrease exponentially with increasing driving voltage frequencies, which have the same tendency under various driving voltage amplitude. Furthermore, the effective d33 values under unipolar driving voltages also decrease approximately exponentially with increasing driving voltage frequencies. For the same peak-to-peak voltage, the effective d33 values under unipolar driving voltages are higher than that of bipolar driving voltages. In conclusion, the actuation performance of PMnS-PZN-PZT based macro fiber composites could be enhanced by adjusting driving voltage amplitude and frequency.

Authors : Eun-Seon Jeong1, Mi-Kyoung Jeon and Jae-Wook Kang
Affiliations : 1Department of Flexible and Printable Electronics, Chonbuk National University

Resume : Organometal halide perovskite have attracted considerable attention over the past several years due to their great potential for photovoltaic applications and recently considered as promising materials in lasing and light emitting device. The on-going reason behind the limitation of the perovskite solar cells (PSCs) performance such as precise controlled of humidity, solvent, crystallinity, temperature, etc are still the main challenging issues. In this report, we investigated in detail the influence of temperature on the photovoltaic parameter of PSCs. The device architecture consist of planar structure of solution processed of PbI2 and methylamoniumiodide (MAI), where the ZnO- nanoridge and 2,2',7,7'-Tetrakis-(N,N-di-4-methoxyphenylamino)-9,9'-spirobifluorene was used as electron and hole transporting layer, respectively. The current-voltage measurement for all sample was recorded by adjusting the temperature using thermoelectric device from 30 up to -40 oC. Based on the results, open circuit voltage (Voc), short circuit current density (Jsc) and fill factor (FF) increased significantly up to –40 oC leading to improvement of power conversion efficiency (PCE). Furthermore, the stability was tested up to 1000 s and found that the photovoltaic parameters such as Voc and FF shows significant increment at 60 s for -20 oC as compared with 0 oC device. This study also highlights that the photovoltaic parameters can be improved by proper controlled of the temperature. It is also noteworthy to mention that this planar heterojunction PSCs obtain higher efficiency at low temperature.

Authors : Jie Shen1, Guangjie Xue1, Jing Zhou1*, Shirley Shen2, Wen Chen1
Affiliations : 1 State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, and School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070, P. R. China 2 CSIRO Manufacturing Flagship, Private Bag 10 Clayton South, VIC 3169, Australia

Resume : The last decade saw little progress on the research on the CaO-Li2O-Sm2O3-TiO2 (CLST) microwave dielectric ceramics due to the complexity in experimental based mechanistic research on dielectric properties. It is mainly influenced by both intrinsicand extrinsic factors. The present study uses the electronic structure calculation with crystal models to evaluate the intrinsic influences of A-site substitutions (Mg2 , Ba2 and Sr2 ) on the dielectric properties of CLST ceramics. In addition, CLST ceramics are prepared using a solid-state reaction and characterized. The electronic structure calculation shows that Mg2 or Ba2 enhances the covalent bond of the crystal, reducing the dielectric loss and permittivity, while Sr2 does the opposite. The experimental results show that Sr2 enters the lattices within the range of substitution amounts, while Ba2 does so only with low substitution content. In these situations, the variation tendencies of the properties with the substitutions agree to the prediction of the electronic structure calculation well, suggesting that intrinsic factors play the main role on the dielectric properties. On the other hand, Mg2 substitution and high content of Ba2 substitution are unable to form homogenous solid solution, since the ion sizes are too small (for Mg2 ) or too big (for Ba2 ), but second phases are formed instead. In these situations, the variation tendencies of the properties with the substitution agree to the two-phase composition rule.

Authors : Alexandre Boulle [1], Ingrid C. Infante [2], Nathalie Lemée [3]
Affiliations : [1] SPCTS – CNRS UMR 7315, Centre Européen de la Céramique, 12 rue atlantis, 87068 Limoges Cedex, France; [2] SPMS Lab. UMR8580 CNRS & CentraleSupélec, Université Paris-Saclay, Grande voie des vignes, 92295 Châtenay-Malabry, France; [3] LPMC, EA 2081, Université de Picardie Jules Vernes, 33 rue Saint Leu, 80039 Amiens, France

Resume : An intrinsic property of materials presenting ferroic orders such as magnetization, polarization and/or deformation is the presence of domains, implying the presence of domain walls. In ferroelectric thin films and multilayers, domains may arrange in the form of periodic 180° stripe-domains of alternating up and down polarization so as to reduce the depolarizing field, hence ensuring charge neutrality at the surface or at the ferroelectric/paraelectric interfaces. These domains give rise to a modulated X-ray diffraction (XRD) signal with satellites near the main Bragg peak. From their position and intensity, both the domain period and relative polarization can be straightforwardly obtained. In this work, we show that a complete simulation of the XRD curves allows the determination of not only the relative polarization and periodicity, but also to have access to the total ferroelectric domain size distribution, as well as to the thickness of the domain wall or the wall roughness and tortuosity. The potential of our model will be illustrated for the case of tricolor PbTiO3/SrTiO3/PbZr0.2Ti0.8O3 superlattices and studied from room temperature up to 900K through ferroelectric transition. We show that the closure of the electric field lines at the ferro/para interfaces is the source of an important ferroelastic strain which can be determined from the XRD curves. We will discuss the possible opening of this model to other ferroic thin films materials presenting structural domains.

Authors : C.Cochard, N.Guiblin, J.M.Kiat, F.Porchet, L. Llopez Conesa, S.Estradé, F.Peiro, Y.Watier, O.Guedes, P.E. Janolin
Affiliations : Laboratoire SPMS, UMR CNRS-CentraleSupelec, Univestité Paris Saclay, Châtenay-Malabry, France; Schlumberger,Clamart, France;Laboratoire Léon Brillouin, UMR 12 CEA/CNRS, CEA/Saclay, Gif-sur-Yvette France; Laboratory of Electron Nanoscopies (LENS), Electronics Department, University of Barcelona, Barcelona, Spain; ESRF The European Synchrotron Grenoble, France

Resume : Piezoelectricity has attracted a considerable interest due to the variety of possible applications such as accelerometers, gyroscopes or transducers. It is known that solid solutions of relaxor and normal ferroelectrics show enhanced piezoelectric properties close to the morphotropic phase boundary (MPB) compared to the end-members. Therefore, materials such as Pb(Mg1/3Nb2/3)O3-PbTiO3 or Pb(Zn1/3Nb2/3)O3-PbTiO3 have been extensively studied over the last 50 years. Pb2(YbNb)O6-PbTiO3 (PYN-PT) perovskite solid solution which is long known to have good piezoelectric properties (d33(ceramic)=510pC/N) and a relatively high Curie temperature (~650K at the MPB), has not received as much attention so far, possibly because single crystal processing is particularly difficult. Besides its evident interest for industrial applications, the study of PYN-PT solid solution will most likely increase the current understanding of antiferroelectrics, ferroelectrics and relaxors materials. Indeed, this solid solution presents the peculiarity of displaying all polar ordering at room temperature depending on the composition. Here, we present the evolution of the crystallographic structures associated with the changes in the polar orders.

Authors : Varun Gandhi, Christian Caspers, Arnaud Magrez, Jean-Philippe Ansermet
Affiliations : Indian Institute of Technology Bombay, Mumbai 400076, India; Laboratoire de Physique des Matériaux Nanostructurés, École Polytechnique Fédérale de Lausanne -- EPFL, CH-1015 Lausanne, Switzerland; Institute of Condensed Matter Physics, École Polytechnique Fédérale de Lausanne -- EPFL, CH-1015 Lausanne, Switzerland; Laboratoire de Physique des Matériaux Nanostructurés, École Polytechnique Fédérale de Lausanne -- EPFL, CH-1015 Lausanne, Switzerland

Resume : Antiferromagnetic (AF) resonances in the multiferroic insulator Bismuth Ferrite (BiFeO3) were detected by high-resolution sub-terahertz spectroscopy using a Vector Network Analyzer (VNA) thanks to its 120 dB dynamic range. We identified antiferromagnetic and magnon features in the frequency range 0.48--0.76 THz. AF resonances showed a clear hysteresis, well distinguishable from that of the magnon peak. We explored the implementation of a lock-in detection based on the VNA.

Authors : Charles Paillard [1], Olivier Copie [1], Charlotte Cochard [1], Pascale Gemeiner [1], Ingrid Cañero-Infante [1], & Brahim Dkhil [1]
Affiliations : [1] Laboratoire SPMS, UMR 8580, CentraleSupélec, CNRS, Université Paris-Saclay, Grande Voie des Vignes 92 295 Châtenay-Malabry CEDEX, France

Resume : The solid solution (1-x)Pb(Ni1/3 Nb2/3)O3-xPbTiO3 (PNN-PT) exhibits relaxor to purely ferroelectric behaviour with large piezoelectric coefficients near the so-called Morphotropic Phase Boundary (MPB) by increasing the PT amount. This is for example the case for many other relaxor-PT systems like PMN-PT, PZN-PT, ... Here, the presence of Ni cations enriches this solid solution by providing potential magnetic and optical features making PNN-PT a multifunctional perovskite oxide. Therefore the structural, electronic, dielectric, piezoelectric, optical and magnetic properties were systematically investigated on a broad range of compositions, ranging from x=0 to x=0.6. We show indeed strong relaxor-like properties (dielectric relaxation, electrostriction) and large piezoelectric coefficient reaching 1000 pC/N at room temperature near the MPB at x=0.35. The optical properties (reflectance, band gap, ...) reveal the absorbance potentialities of PNN-PT in the visible and UV range. In addition, the study of the lattice constant with temperature, coupled to calorimetric experiments, point to a possible Jahn-Teller distortion related to low to high spin transition of the Nickel ion near room temperature for solid solution with low PT content.

Authors : C. Cochard1,2, R. Faye1, I. C. Infante1, V. V. Shvartsman3, D.?C.?Lupascu3, O. Guedes2, and P.-E. Janolin1*
Affiliations : 1SPMS Laboratory, UMR8580 CNRS & CentraleSupelec Grande Voie des Vignes, Chatenay-Malabry, France, F-92295 2Riboud Product Center, Schlumberger 1 rue H. Becquerel, Clamart, France, F-92410 3Institute for Materials Science, University of Duisburg-Essen and Centre for Nanointegration Universit?tsstrasse 15, Essen, Germany, D-45141

Resume : In contrast to ferroelectrics, antiferroelectrics have received less attention despite rich and still yet understood phenomena making them of interest for academic research as well as for potential applications including high-energy storage capacitors, electrocaloric devices, or sensors and transducers. Several phonon mode instabilities are known to exist in antiferroelectrics like in the prototypal PbZrO3 (PZ) system. Such instabilities imply antiparallel and/or ferroelectric displacements as well as in-phase and/or antiphase oxygen octahedra tiltings. It is believed, but still debated, that these modes compete and/or may couple leading to antiferroelectric behavior. By destabilizing these modes, it is then possible to get various polar states. As examples, PZ goes through a peculiar ferroelectric state with temperature increasing prior to the paraelectric state or Pb(Yb1/2Nb1/2)O3-PbTiO3 (PYN-PT) solid solution which can exhibit all polar orders at room temperature, thus leading to antiferroelectric, classical ferroelectric, or relaxor properties increasing PT amount. While the behavior of antiferroelectrics was recently reconsidered, only few works using local probes to reveal the polar features have been published. In this work, we use piezoresponse force microscopy (PFM) to get insight into the local features of induced polar arrangements as a function of electric field and temperature in these systems. After recalling structural and electric features on the above mentioned compounds deduced from larger scale techniques including X-ray diffraction and neutron scattering, Raman and dielectric spectroscopies, as well as macroscopic piezoelectric and ferroelectric measurements as a function of temperature we will reveal the local phenomena underneath these properties seen by PFM. As a result, we evidence on PZ single crystals the arising of a piezoelectric response through the antiferroelectric to ferroelectric phase transformation and its time-dependent evolution by performing PFM mappings as a function of temperature. On PYN-PT ceramics of various compositions, we show the room temperature studies, including local piezoelectric loops to explore compositions with low PT content near the antiferroelectric end-member (0≤x≤0.16) and direct imaging of virgin and induced domain patterns characteristic of relaxor, ferroelectric-relaxor, and ferroelectric materials (0.20≤x≤0.60). In the latter case, we will confirm and complete with these PFM studies the PYN-PT phase diagram, showing the antiferroelectric order from local piezoelectric loops, and studying for virgin and artificial polar domains the coherence lengths and the corresponding temperature transition, respectively. These results will be presented within the global picture of the piezoresponse microscopy studies comparing antiferroelectrics with relaxors and ferroelectrics.

Authors : Z. Othmen1,2, K. Daoudi1,3, R. Othmen1,4, A. Madouri4, M. Oueslati1 and B. Dkhil2
Affiliations : 1 Unité Nanomatériaux et Photonique, Faculté des Sciences de Tunis, Université de Tunis El Manar, 2092, Tunis, Tunisie. 2 Laboratoire Structures, Propriétés et Modélisation des Solides, CNRS-UMR 8580, CentraleSupélec, Université Paris-Saclay, France. 3 Department of Applied Physics, College of Sciences, University of Sharjah, P.O. Box 27272, Sharjah, United Arab Emirates. 4 CNRS/LPN, Route de Nozay, F-91460 Marcoussis, France.

Resume : Since the discovery of graphene a huge interest has been devoted to this material in view of its integration in various technological applications ranging from nanometric electronic devices to large scale solar cells. So far, the deposition of a thin monolayer of graphene has been achieved using various techniques on various substrates materials. In order to extend our knowledge and benefit from the amazing electronic properties of this material we have here successfully transferred a graphene layer on top of a La0.7 Sr0.3CoO3 (LSCO) perovskite oxide thin film using chemical vapor deposition technique and studied its consequence on the Co spin state and local structure distortions. Indeed, LSCO cobaltites [3] are known to be mixed-valence systems (Co3+/Co4+ ) characterized by rich and complex physical properties. The Co-ions (Co3+ ) and (Co4+ ) are able to take three different spin states: low-spin (LS), intermediate-spin (IS) and high-spin (HS) states. The predominant spin state in 20nm-thick film of LSCO grown on LaAlO3 substrate is the LS state where Jahn-teller (J-T) lattice distortions are inactive in contrast to the IS state. Using Raman spectroscopy we unambiguously show that the J-T active Raman modes are induced in the Graphene/LSCO nanostructure which drastically differs to the situation of LSCO without graphene. This observation is attributed to a charge transfer from graphene to LSCO promoting the IS states which in turn activates the J-T Raman modes.

Authors : Jie Wei, 1, 2 Yang Liu, 1 Xiaofei Bai, 1 Chen Li, 2 Yalong Liu, 2 Zuo Xu, 2 Raphael Haumont, 3 Ingrid C. Infante, 1 and Brahim Dkhil 1
Affiliations : 1 Laboratoire Structures, Propriétés et Modélisation des Solides, CNRS-UMR8580, CentraleSupélec, Université Paris-Saclay, 92295 Chatenay-Malabry Cedex, France 2 Electronic Materials Research Laboratory, Key Laboratory of Ministry of Education & International Center for Dielectric Research, Xi'an Jiaotong University, Xi'an 710049, P. R. China 3 Laboratoire de Physico-Chimie de l'Etat Solide, ICMMO, CNRS-UMR 8182, Bâtiment 410 -Université Paris-Sud XI, 15 rue Georges Clémenceau 91405 Orsay Cedex, France

Resume : Sc-doped BiFeO3 (BFO) ceramics synthesized by a facile solid-state sintering route were characterized by X-ray diffraction, magnetic and electrical measurements. Our data reveal that Sc substitution reduces the leakage current and enhances the multiferroic properties of BFO. By replacing Fe3+ time to time with non-magnetically active Sc3+, Sc substitution induces a weak ferromagnetism by triggering a ferromagnetic-like coupling rather than an AFM super-exchange. Simultaneously, a well saturated polarization value and polarization switching under low driving field are achieved due to the combined effect of both the polar distortion and reduced leakage current density. A bulk limited Poole–Frenkel emission behavior we evidenced in Sc-doped BFO ceramics gives a zero-field trap ionization energy of 0.99 eV suggesting that the likely trap centers are oxygen vacancies.

Authors : Annette Bussmann-Holder & Krystian Roleder
Affiliations : Institute of Physics; University of Silesia, Katowice, Poland

Resume : Early measurements by Courtens [1] suggested that the birefringence in the ferroelastic phase varied with temperature with a critical exponent for the order parameter of 0.36(2). More recent measurements [2], in which birefringence imaging was used to make sure that a domain-free region of the crystal was measured, revealed a mean-field exponent close to 0.5. It was suggested that Courten’s measurement, which was carried out by averaging over a field of view of the crystal, might have been affected by the presence of domains appearing within the low-temperature phase. More importantly for the purposes of this report, Courtens observed a curious cusp appearing just above the phase transition that he explained in terms of critical fluctuations. Such behavior was not seen in the work [2]. In this report we will show that this cusp can be avoided if only phase transition is observed at no change in the indicatrix orientation during structural transformation (Fig 2). At the same time the temperature behavior of birefringence below TS is not pointing to purely displacive type transition. Above Ts the precursor dynamics is present [3] independently on crystal technology and its temperature range is in good agreement with temperature range reported also for micro- and nanoceramics of SrTiO3 by Hehlen et al [4]. 1. E. Courtens, Phys. Rev. Letters, 29, No. 20, 1972 2. M. A. Geday and A. M. Glazer, J. Phys.: Condens. Matter 16, 3303–3310, 2004 3. K. Roleder, A. Bussmann-Holder, M. Górny K. Szot and A. M. Glazer, Phase Transitions, 85, No. 11, 939–948, 2012 4. B. Hehlen, A. Al-Zein, C. Bogicevic, P. Gemeiner, and J-M. Kiat, Phys. Rev. B87, 014303 (2013)

Authors : L. Szymczak, A. Soszyński
Affiliations : Institute of Physics, University of Silesia, ul. Uniwersytecka 4, 40-007 Katowice, Poland

Resume : Ferroelectric Ba1−xSrxTiO3 (BST) ceramics are of great technological interest. Due to its large pyroelectric coefficient, high dielectric permittivity, low dielectric losses and high dielectric breakdown strength, the ferroelectric BST has recently been identified as promising candidate for an inexpensive infrared thermal imaging device called uncooled infrared focal plane arrays [1]. The BST, especially due to its high dielectric permittivity, may replace the current silicon oxide and nitride dielectrics to build up next generation of dynamic random access memories, which require higher integration densities [2]. In addition, the strong dependence of dielectric permittivity on electric field [3] makes them attractive for application in voltage-tunable microwave devices such as filters, tunable oscillators, delay lines, and phase shifters [4], which are essential elements in communication and radar systems [5]. The dielectric properties of BST can be modified not only by controlling the Ba/Sr ratio but also through partial substitution of iso- or heterovalent cations in A and/or B-sites in ABO3 perovskite structure [6, 7, and 8]. The influence of rare earth oxides such as Dy2O3, Er2O3 and Sm2O3 on the structural and dielectric properties of barium strontium titanate ceramics has recently been extensively investigated [9, 10, and 11]. However, information about La2O3-doped BST ceramics, especially of the temperature dependence of dielectric parameters, is scarce [12-17]. In this report the results of experimental studies of the influence of La2O3 on the grain structure, phase transitions and dielectric properties of (Ba0.8Sr0.2)TiO3 (BST 80/20) ceramics will be presented. The La concentrations in ceramics, which were prepared by conventional mixed oxide method, was changing from 0.5 to 2 mol. %. The unit cell parameters were determined from the x-ray diffraction measurements, and scanning electron microscope JSM 5410 with an energy dispersive X-ray spectrometer (EDS) was used to reveal the grain structure and chemical composition of ceramics obtained. Detailed studies of dielectric permittivity as function of temperature and frequency showed that these compounds undergo a diffuse phase transition. Measurements of the pyroelectric and thermally stimulated depolarization currents have confirmed character of this transition. References: [1] S. Liu, M. Liu, Y. Zeng, and Y. Huang, Mat. Sci. Eng. B90, 149, (2002). [2] A. I. Kongon, S. K. Streiffer, C. Basceri, and S. R. Summerfelt, Mater. Res. Bull. 46, (1996). [3] S. Lahiry and A. Mansingh, Ferroelectrics 306, 37, (2004). [4] F. Zimmermann, M. Voights, C. Weil, R. Jakoby, P. Wang, W. Menesklou, and E. Ivers-Tiffe, J. Eur. Ceram. Soc. 21, 2019, (2001). [5] S.-G. Lee, C.-I. Kim, J.-P. Kim, and S.-H. Lee, Mater. Lett. 58, 110, (2004). [6] L.Szymczak. L.Kozielski, M.Adamczyk, A.Lisińska-Czekaj, D.Czekaj, Z.Ujma, Ferroelectrics, 349, 179-189, (2007). [7] L.Szymczak, Z.Ujma, M.Adamczyk, M.Pawełczyk, Ceramics International, 34, 1993-2000, (2008). [8] L.Szymczak, M.Adamczyk, M.Pawełczyk, Archives of Metallurgy and Materials, 54(4), 943-949, (2009). [9] Huang X Y, Gao C H, Chen X C, Zheng X L, Huang G J, Liu H P., J Rare Earths, 22(z3): 226−228, (2004). [10] Jingji Zhang, Jiwei Zhai, Xiujian Chou, Xi Yao, Materials Chemistry and Physics, 111,409, (2008). [11] Li Y, Qu Y. J., Mater Res Bull, 44(1): 82−85, (2009). [12] Ling Dong, Xu Guo-yue, Cai Shaoa, J. of Optelectronics and Advanced Materials, 7(5), 2737 -2742, (2005). [13] RH Liang, XL Dong, Y Chen, et al., Materials Chemistry and Physics, 95(2-3), 222-228, (2005). [14] XH Wang, WZ Lu, J Liu, et al., J. Eur. Ceram. Soc., 26(10-11), 1981-1985, (2006). [15] Chunlai Xu, Heping Zhou, Key Engineering Materials, 336-338(1-3), 249-251, (2007). [16] Yanhua Fan, Shuhui Yu, Rong Sun, et al., Applied Surface Science, 255(20) 8319-8323, (2009). [17] C. R.Gautam, A. K.Yadav, P.Singh, Materials Research Innovations, 17(3), 148-153, (2013).

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Emerging materials and functions : P. Paruch
Authors : Hiroki Taniguchi
Affiliations : Department of Physics, Nagoya University

Resume : Ferroelectric oxides have conventionally developed with oxides mainly composed of oxygen-octahedra, which are represented by perovskite-type compounds such as BaTiO3, Pb(Zr,Ti)O3, BiFeO3, and so on. Though their various ferroic properties are fascinating topics in the field of physics and materials science, the discovery of new ferroelectrics in the octahedra-based oxides seems to be gradually saturating in these days. There is thus increasing demand for mining new ferroelectric systems by expanding the area of exploration. Our group recently focused on the development of new ferroelectric oxides, which are mainly composed of oxygen tetrahedra, in particular SiO4 and AlO4. An advantage of the oxygen-tetrahedra-based oxides is their environmental affinity and natural abundance, since most of rock-forming oxides in the earth?s crust are known to be formed by the oxygen-tetrahedra. There are however very few tetrahedra-based-oxides reported to show ferroelectricity, except for water-soluble phosphates and phosphites that are generally difficult to apply for modern electronics. Here I show the bismuth silicates, Bi2SiO5, whose ferroelectricity has recently been demonstrated by our group. Based on the mechanism of ferroelectricity clarified in Bi2SiO5, I will discuss the designing principle of new tetrahedra-based ferroelectric oxides by introducing some examples in ferroelectric stuffed-zeolites.

Authors : M. Campbell, J. R. Whyte, R. G. P. McQuaid, A. Kumar, J. M. Gregg
Affiliations : Queens University Belfast

Resume : Over the last decade there has been an explosion of interest in sheet conductors, such as surface states in topological insulators [1], LaAlO3 -SrTiO3 interfaces [2] and graphene [3]. Recent research has shown that ferroic domain walls constitute another exciting group of 2D conductors, with probably even greater potential than those already known: after all, domain walls have special properties that other systems do not have in that they are mobile, can be controllably shunted from point to point, and can be spontaneously created, or made to disappear. Luckily for the research community, the field of ?domain wall nanoelectronics? [4] is still young and there is a great deal, in terms of fundamental science, still to be uncovered. This talk will concentrate on two areas of domain wall research recently performed at Queen?s University Belfast: firstly, experiments revealing fundamental insight into domain wall conduction mechanisms will be described. Specifically, the use of scanning probe microscopy to determine Hall voltages at domain walls will be discussed, as will the active carrier types, mobilities and densities implied in both rare earth manganites and metal-halide boracites (both improper ferroelectrics with transport-active ?head-to-head? and ?tail-to-tail? walls). Secondly, various ways in which domain wall injection and motion [5] have been controlled, using sample morphology, electric and stress fields, will be described which have culminated in the successful creation of a ferroelectric domain wall diode [6]. [1] H. Zhang et al. Nature Physics 5, 438 (2009) [2] A. Ohtomo and H. Y. Hwang, Nature 427, 423 (2004) [3] K. S. Novoselov et al. Science 306, 666 (2004) [4] G. Catalan et al. Rev. Mod. Phys. 84 119 (2012) [5] J. R. Whyte et al. Adv Mat. 26, 293 (2014); J. R. Whyte et al. J. Appl. Phys. 116, 066813 (2014) [6] J. R. Whyte et al. Nat. Comms (in press 2015)

Authors : V. Stepkova, P. Marton, J. Hlinka
Affiliations : Insitute of Physics, Czech Acad. Sci.

Resume : Phase-field simulations demonstrate that the polarization order-parameter field in the Ginzburg-Landau-Devonshire model of rhombohedral ferroelectric BaTiO3 allows for an interesting linear defect, stable under simple periodic boundary conditions. This linear defect, termed here as Ising line, can be described as about 2 nm thick intrinsic paraelectric nanorod acting as a highly mobile borderline between finite portions of Bloch-like domain walls of the opposite helicity. These Ising lines play the role of domain boundaries associated with the Ising-to-Bloch domain wall phase transition.

Authors : Y. Liu1, I.C. Infante1, P.E. Janolin1, XJ Lou2, XB Ren2, W. P. Geng3, A. Q. Jiang3, X. J. Meng4, D.C. Lupascu5, L. Bellaiche6, J. F. Scott7, B. Dkhil1
Affiliations : 1Laboratoire Structures, Propriétés et Modélisation des Solides, UMR8580, CentraleSupélec, CNRS, Université Paris-Saclay, 92290 Châtenay-Malabry, France 2Multi-disciplinary Materials Research Center, Frontier Institute of Science and Technology, and State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, P. R. China 3State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai, 200433, P. R. China 4National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Yu Tian Road 500, Shanghai 200083, P. R. China, University of Chinese Academy of Sciences, No. 19A Yuquan Road, Beijing 100049, China 5Institute for Materials Science, University of Duisburg-Essen and Center for Nanointegration Duisburg-Essen (CeNIDE), Essen 45141, Germany 6Physics Department and Institute for Nanoscience and Engineering, University of Arkansas, Fayetteville, 72701 Arkansas, USA 7Department of Physics, Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, UK and Departments of Chemistry and Physics, St. Andrews University, St. Andrews, Scotland KY16 9ST

Resume : The search for alternative solid-state refrigeration materials to hazardous gases in conventional and cryogenic cooling devices is a very active field of condensed matter. The use of phase transitions is a powerful tool to achieve giant caloric effects in ferroic materials in which magnetization, polarization, strain and/or volume can be strongly tuned under a moderate external stimulus. Here, we explored various phenomena existing in ferroelectrics to reveal their potentialities as solid state coolers. By using Landau-based phenomenological calculations, we studied the elasto- and electro-caloric properties of the model and ecofriendly BaTiO3 in details including bulk and thin film form, the role of the external uniaxial stress, electric field, substrate, film thickness and electrodes. We show that ferroelectrics are natural multicaloric materials in which both giant elasto- and electro-caloric responses can be achieved near room temperature and that the 2nd-order nature of transitions can be beneficial. We also investigated how multiphase points composition can be used to enhance electrocaloric effects. Moreover, in addition to conventional electrocaloric effect, we show that negative effect can be also generated efficiently and thus used as a supplemental tool for designing enhanced caloric responses. As a conclusion, our findings clearly demonstrate promising perspectives for ferroelectrics in solid-state refrigeration.

10:30 Coffee break    
Lead-based model perovskites : K. Roleder
Authors : B. Hehlen, M. Al-Sabbagh, A. Al-Zein, J. Hlinka
Affiliations : Laboratoire Charles Coulomb (L2C), University Montpellier and CNRS, Place E. Bataillon, Montpellier, France; Laboratoire Charles Coulomb (L2C), University Montpellier and CNRS, Place E. Bataillon, Montpellier, France; European Synchrotron Radiation Facility (ESRF), 71 Avenue des Martyrs, Grenoble, France; Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 18221 Praha 8, Czech Republic

Resume : Hyper-Raman scattering (HRS) is a non-linear inelastic spectroscopy sensitive to polar excitations in solids whatever their crystalline symmetry. This selection rule is very attractive in particular for centro-symmetric structures for which polar modes are inactive in Raman. HRS has been performed in the cubic relaxors PbMg1/3Nb2/3O3 (PMN) and PbMg1/3Ta2/3O3, with particular attention to the low frequency region, down to 2 cm-1. Spectra have been recorded over a wide temperature range (900K-30K in PMN) providing therefore the framework for a detailed analysis of the polarization dynamics in these systems. In both materials, the soft mode response exhibits a doublet structure up to the highest temperature investigated [1,2] emphasizing a common property of cubic relaxors. The lowest frequency component is assigned to the primary soft mode of symmetry F1u, while the second likely originates from a local disorder persisting until very high temperatures and lifting the cubic selection rules. On cooling, the soft F1u-mode of PMN becomes overdamped at the onset of the Burns temperature, but very interestingly it splits between 600K and 400K into two components which harden on decreasing further the temperature. This behavior likely highlights the onset of a local anisotropy of the polarization and provides therefore new insight about the relaxor nature. 1. A. Al-Zein, et al. Phys. Rev. Lett. 105, 017601 (2010) 2. S.B. Vakhrushev, et al. Phys. Solid State, 52, 889 (2010)

Authors : J. Hlinka
Affiliations : Insitute of Physics, Czech Acad. Sci.

Resume : Solid solutions of lead-based perovskites are often showing either a ferroelectric transition with a glassy dynamics or enhanced piezoelectric properties. The IR spectroscopy of lead-based relaxors is well understood[1], but the assignment of Raman spectra remains problematic. The Raman activity originates from both the occupational ordering [2] and the ionic off-centering [3]. The weight of these effects changes from one material to another. Morever, the inherent disorder lifts the strict Raman selection rules, while the Hyper-Raman scattering spectra obey the polarization selection rules rather well [4]. Still, Raman scattering in relaxors shows a measurable polarization dependence and specific features of Raman scattering can be even employed to probe relaxor to ferroelectric crossover [5] or to distinguish between distinct ferroelectric phases coexisting in materials with compostion close to the so-called MPB boundaries[6]. Here, our recent polarized Raman scattering studies of relaxors will be discussed. 1. JH et al, Phase Transitions, 79, 41 (2006). 2. Setter N and Laulicht I, Appl. Spectrosc., 41, 526 (1987). 3. Iwata M, et al, Jpn. J. Appl. Phys., 40, 5819 (2001). 4. A. Al-Zein, et al, Phys. Rev. B, 78, 134113 (2008); Phys. Rev. Lett. 105, 017601(2010). 5. Maier B et al, Phys. Rev. B, 79, 224108 (2009). 6. I. Rafalovskyi, et al, arXiv:1304.1879 (2013). 7. J. Pokorný et al, J. Adv. Phys. 5, 1550013 (2015).

Authors : A.M. Glazer, Nan Zhang, M. Pasciak, M. Guttmann, T.R. Welberry, K. Roleder, J. Hlinka and Zuo-guang Ye
Affiliations : Physics Department, Oxford University, UK; Chemistry Department, Simon Fraser University, Vancouver, Canada; Academy of Sciences, Czech Republic; Rutherford Appleton Laboratory, UK; Research School of Chemistry, ANU, Canberra, Australia; Institute of Physics, Silesian University, Katowice, Poland; Academy of Sciences, Czech Republic; Chemistry Department, Simon Fraser University, Vancouver, Canada

Resume : A combined neutron diffuse scattering study and model analysis of the antiferroelectric crystal PbZrO3 is described. Clear evidence for disordering of oxygen octahedral tilts and Pb displacements is found in the high-temperature cubic phase. Extra scattering is found at M and R points in the Brillouin zone. A Molecular Dynamics simulation closely reproduces the diffuse scattering pattern. The arrangements of the plus (in-phase) and minus (antiphase) tilt systems are discussed according to the model. The transition between disordered and ordered local structure is discussed and compared with that seen in Zr-rich PbZr1-xTixO3.

Authors : Pierre-Eymeric Janolin, Romain Faye, Charlotte Cochard
Affiliations : Laboratoire SPMS Universite Paris Saclay, CentraleSupelec, CNRS

Resume : We shall present our recent results on antiferroelectrics and antiferroelectric-based solid solutions, focusing on the atomistic origin of the wealth of extraordinary properties they exhibit when combined with ferroelectrics or magnetic materials. Starting with the model antiferroelectric lead zirconate (PbZrO3), we shall explain why the transitional phase between the high-temperature cubic phase and the room-temperature antiferroelectric phase is not always observed as well as its origin and properties. The proximity in energy with ferro- and para-electric phases will also be discussed from the behavior of PbZrO3 under high pressure, investigated from 1st-principles and experimental results. We shall also review the possibilty to engineer materials through the influence of chemical order on the onset of antiferroelectricity. After reviewing double-perovskites in general, we shall focus on lead ytterbium niobate (PYN: PbYb1/2Nb1/2O3 or Pb2YbNbO6). This material is of particular interest as its solid solution with lead zirconate (PbTiO3) exhibits all polar orders of applicative interest at room temperature, notably high-temperature high-piezoelectric constants that surpass lead zirconate titanate ones. The comparative study of the microscopic displacement patterns in the two solid solutions (PbZrO3-PbTiO3 and PYN-PbTiO3), both based on antiferroelectrics, will shed a new light on the building blocks of high-performance perovskite functional materials. The last part of the presentation will review another avenue to engineer novel properties by presenting the solid solution between an antiferroelectric material (still PbZrO3) and a magnetic perovskite (PbFe2/3W1/3O3). Short- and long-range interactions exist in both end-members. This multiferroic solid-solution exhibits not only polar and magnetic orders but also couplings of different kinds and at different length-scales, including bi-relaxors, combining the high-performances of ferroelectric relaxors with multiferroicity

Authors : E. Buixaderas 1, I. Gregora 1, J. Hlinka 1, F. Cordero 2, F. Craciun 2, C. Galassi 3
Affiliations : 1 Institute of Physics, Czech Academy of Sciences, Prague, Czech Republic 2 CNR-ISC, Istituto dei Sistemi Complessi, Roma, Italy 3 CNR-ISTEC, Istituto di Scienza e Tecnologia dei Materiali Ceramici, Faenza, Italy

Resume : Antiferroelectricity has aroused again a lot of attention, due to the new possibilities for application in devices because of its natural nano-domain structure. The prototypic antiferroelectric material is PbZrO3. However, its antiferroelectric behaviour is also in competition with a polar instability. It is, therefore, not surprising that PbZrO3 becomes ferroelectric under electric field, pressure or small ionic substitution. Small amounts of Ti induce an intermediate ferroelectric phase on cooling from the paraelectric phase, prior to the achievement of its antiferroelectric ground state. We have studied the intermediate ferroelectric states in Pb(Zr,Ti)O3, with about 5% of Ti. Dielectric, inelastic and Raman experiments show that there are several intermediate ferroelectric states in these ceramics, very dependent on the thermal pre-history of the samples. The availability of these states near room temperature depends on the delicate thermal treatment of the sample and the heating and cooling rates. A good understanding of this effect will help to develop better antiferroelectric-ferroelectric devices.

Authors : H. Safa Aydın, Volkan Kalem
Affiliations : Department of Metallurgical and Materials Engineering, Selcuk University, 42130, Konya/Turkey

Resume : The effect of Sr doping on dielectric and piezoelectric properties, Curie temperature (Tc), and microstructure of PMN-PT solid solutions were studied. The Sr-modified ceramics with a composition (Pb1-xSrx)[(Mg1/3Nb2/3)0.67Ti0.33]O3 (x= 0 – 0.10) were prepared by conventional solid state sintering method. Dielectric and piezoelectric properties of the doped ceramics were measured at room temperature. The experimental results showed that the strontium doping in this system results in a reduction of grain size, a downward shift in Tc, and decreased tetragonality. Compositions with x = 0.02-0.04 exhibited maximum dielectric constant, electromechanical coupling factor and piezoelectric strain constant. Based on this investigation, Sr doped PMN-PT compositions are considered to be good candidates for sensor and actuator applications.

12:45 Lunch break    
Thin films and superlattices I : P. Thomas
Authors : Patrycja Paruch
Affiliations : DQMP, University of Geneva, Switzerland

Resume : Interfaces in oxides - whether artificially introduced in superlattices or present intrinsically as ferroic domain walls - provide pathways to novel functional behaviour such as electronic transport properties or coupling between different order parameters, all at a very localised scale. Here we report on such interfaces, focusing in particular on the role of electrostatic and strain boundary conditions. We explore the complex phase diagram of epitaxial BiFeO3/LaFeO3 superlattices [1] grown on (001) SrTiO3 and (110) DyScO3 substrates, presenting three distinct regions as a function of BiFeO3 fraction, with a BiFeO3-like ferroelectric phase and a LaFeO3-like paraelectric phase at its extremities, and a complex intermediate region, as supported by first principles calculations. The intermediate region shows unusual, mixed functional behavior, most likely due to competing phases driven by substitution with a same-size central ion and the specific boundary conditions imposed by the superlattice structure, with much more diffuse transitions observed for the samples grown on SrTiO3. In epitaxial ferroelectric Pb(Zr,Ti)O3 thin films, we investigate on the effects of surface adsorbates and oxygen vacancy redistribution on the electrical conduction at domain walls. In SrTiO3-based films, domain-wall-specific conduction is present with no additional treatment [2]. In DyScO3- based films, we observe reversible switching between conducting and insulating behaviour at 180° domain walls following ultrahigh vacuum thermal annealing vs. ambient exposure, respectively [3]. 1. Rispens et al, Phys. Rev. B. 90, 104106 (2014) 2. Guyonnet et al, Adv. Mat. 23, 5377 (2011) 3. Gaponenko et al, Appl. Phys. Lett. 106, 162902 (2015)

Authors : Pavlo Zubko [1], Jacek Wojdel [2], Marios Hadjimichael [1], Stephanie Fernandez [3], Anais Sene [4], Igor Luk’yanchuk [4], Jean-Marc Triscone [3], Jorge Iniguez [5,2]
Affiliations : [1] London Centre for Nanotechnology, University College London, London, UK [2] Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Barcelona, Spain [3] Department of Quantum Matter Physics, University of Geneva, Geneva, Switzerland [4] Laboratory of Condensed Matter Physics, University of Picardie, Amiens, France [5] Materials Research and Technology Department, Luxembourg Institute of Science and Technology (LIST), Luxembourg

Resume : Ferroelectrics are already firmly established as some of the most useful functional materials with a broad range of applications in non-linear optics, thermal imaging, electromechanical elements and electronics. Furthermore, there is hope that recent advances in our understanding of nanoscale ferroelectricity may enable this list to be further expanded with devices such as ferroelectric tunnel junctions, memristors and ferroelectric field effect transistors. Among the many fascinating properties of nanoscale ferroelectrics, the possibility of using them as negative capacitance elements has recently been attracting significant interest in part due to the potential benefits it may bring to the operation of field effect transistors [1]. The negative capacitance phenomenon relies on the imperfect screening of the ferroelectric polarisation, which can be engineered in a controlled manner in artificially layered systems such as ferroelectric-dielectric superlattices. We have used dielectric impedance spectroscopy to investigate the dielectric properties of such superlattices exhibiting negative capacitance effects over a broad range of temperatures. The results are interpreted using phenomenological modelling and atomistic simulations, which reveal the crucial role played by the ferroelectric domain structure in the dielectric properties of these artificially layered materials. [1] Salahuddin, Datta, Nano Letters 8, 405 (2008)

Authors : A.Mercy, J.Varignon, E. Bousquet, Ph. Ghosez
Affiliations : Theoretical Materials Physics, Université de Liège Allée du six août 17, B-4000 Sart Tilman, Belgium

Resume : Oxides perovskites attract widespread interest due to the large scope of their functional properties, including ferroelectricity, magnetism, superconductivity, giant magnetoresistance to name a few. Among them, the members of the R3+Ni3+O3 family (1,2,3,4,5), display an interesting phase diagram. As the temperature decreases, they undergo a metal to insulator phase transition (MIT), linked to the appearance of a charge ordering/charge disproportionation and a symmetry change from Pbnm to P21/n. The only exception is LaNiO3, which adopts a R-3c phase and remains metallic (6). The charge ordering is crucial for the MIT, as it splits the eg d levels between neighboring Ni3+ sites (t2g6eg1) in two different eg occupations: t2g6eg2 (Ni2+) and t2g6eg0 (Ni4+). Moreover, this specific charge ordering is compatible with complex magnetic structures that can further give rise to improper ferroelectricity and the appearance of a sizable spontaneous polarization (3,4). Many efforts have already been devoted to the characterization of those systems. Unfortunately, standard DFT methods typically fail to reproduce their correct ground state, both in terms of symmetry and magnetic properties (3,4,5). In the present work, we report symmetry analysis and first-principles study of selected bulk R3+Ni3+O3 nickelates. Firstly, we show that our DFT approach, based on the hybrid B1WC functional (7), is able to reproduce the proper ground state symmetry and properties. This allows us to re-discuss, in bulk systems, the interplay between various structural degrees of freedom (ferroelectric, AFD rotational motions, oxygen breathing, Jahn-Teller distortions) and the orbital, charge and magnetic orderings and to identify possible new functionalities. Secondly, we discuss the influence of epitaxial strain and layering on the properties of bicolor nickelates superlattices, including the possible appearance of hybrid improper ferroelectricity. Work supported by the ARC project “TheMoTherm” and F.R.S-FNRS project “HiT4FiT”. Ph. Ghosez also acknowledges a Research Professorship of the Francqui Foundation. 1. Electric-Field Control of the Metal-Insulator Transition in Ultrathin NdNiO3 Films. R. Scherwitzl, P. Zubko, I. Gutierrez Lezama, S. Ono, A. F. Morpurgo, G. Catalan and J.-M. Triscone, Adv. Mat. 22, 5517 (2010). 2. Metal-Insulator Transition in Ultrathin LaNiO3 Films. R. Scherwitzl, S. Gariglio, M. Gabay, P. Zubko, M. Gibert and J.-M. Triscone, Phys. Rev. Lett. 106, 246403 (2011). 3. Multiferroicity in Rare-Earth Nickelates RNiO3, G. Giovannetti, S. Kumar, D. Khomskii, S. Picozzi and J. van den Brink, Phys. Rev. Lett. 103, 156401 (2009). 4. Rationalizing strain engineering effects in rare-earh nickelates. F. Y. Bruno, K. Z. Rushchanskii, S. Valencia, Y. Dumont, C. Carrétéro, E. Jacquet, R. Abrudan, S. Blügel, M. Lezaic, M. Bibes and A. Barthélémy, Phys. Rev. B 88, 195108 (2013). 5. Ab initio study of the factors affecting the ground state of rare-earth nickelates. S. Prosandeev, L. Bellaiche and J. Iñiguez, Phys. Rev. B 85, 214431 (2012). 6. Exchange Interaction in the Insulating Phase of RNiO3. J.-S. Zhou, J. B. Goodenough and B. Dabrowski, Phys. Rev. Lett. 95, 127204 (2005). 7. Hybrid exchange-correlation functional for accurate prediction of the electronic and structural properties of ferroelectric oxides. D. I. Bilc, R. Orlando, R. Shaltaf, G.-M. Rignanese, J. Iñiguez and Ph. Ghosez, Phys. Rev. B 77, 165107 (2008).

Authors : A.M. Schober[1], M.C. Weber[1], M. Guennou[1], J. Fowlie[2], J. -M. Triscone[2], J. Kreisel[1]
Affiliations : [1] LIST Luxembourg Institute of Science and Technology, 41 rue du Brill, 4422 Belvaux, Luxembourg. [2] DPMC, University of Geneva, 24 Quai Ernest-Ansermet, 1211 Genève 4, Switzerland

Resume : Rare earth nickelates ReNiO3 have been intensively studied over the recent years for their magnetic properties as well as their very sharp metal-insulator transition. This transition can be tuned by the size of the rare-earth, so that the behavior changes in the series. LaNiO3, in particular, is metallic at all temperatures, making it an ideal electrode material for oxide-based electronics. This led to many subsequent investigations to unveil the tuning of their physical response to external parameters such as temperature and epitaxial strains. Here, we report experimental investigations of ReNiO3 nickelates films (Re = La, Nd) on LAO substrates down to 3 unit cells by Raman spectroscopy, performed with the aim to explore the stability limit of the bulk structure for ultrathin films. This complements earlier results obtained on similar films down to 15 nm[1] (approx. 40 unit cells), which had revealed a first symmetry lowering from the rhombohedral ground state of LaNiO3. Changes in the Raman signature for the ultrathin films give evidence for further structural changes. Methods for extraction of the Raman signature of those extremely thin films will also be discussed. [1] M.C. Weber a,b, M. Guennou a, D. Pesquera c, J. Fontcuberta c, J. Íñiguez c, J. Kreisel a,b, Strain-induced symmetry breaking in LaNiO3 thin films, EMRS Fall meeting 2014.

15:30 Coffee break    
Thin films and superlattices II : M. Viret
Authors : Massimiliano Stengel
Affiliations : Institut de Ciencia de Materials de Barcelona (ICMAB-CSIC); ICREA - Institució Catalana de Recerca i Estudis Avançats

Resume : Flexoelectricity describes the electric polarization that is linearly induced by a strain gradient, and is being intensely investigated as a tantalizing new route to converting mechanical stimulation into electrical signals and vice versa. While several breakthough experiments have been reported in the past few years, progress on the theoretical front has been comparatively slow. The main difficulty with calculating the flexoelectric response of a material is the inherent breakdown of translational periodicity that a strain gradient entails, which at first sight questions the very applicability of traditional plane-wave pseudopotential methods. In this talk I will show how these obstacles can be overcome by combining density-functional perturbation theory with generalized coordinate transformations, gaining access to the full microscopic response (in terms of electronic charge density, polarization and atomic displacements) of a crystal or nanostructure to an arbitrary deformation field. As a practical demonstration, I will present results on the full flexoelectric response of SrTiO3, including atomic relaxations and surface effects. I will show that, upon bending a macroscopically thick SrTiO3 slab, one obtains a positive or a negative voltage depending on the crystal lattice termination, which points to a dramatic dependence of the flexoelectric effect on the details of the sample surface.

Authors : Lee C. Phillips, Pascale Gemeiner, Vincent Garcia, Stephane Fusil, Edouard Lesne, Eric Jacquet, Brahim Dkhil, Manuel Bibes, Agnes Barthelemy
Affiliations : Unité Mixte de Physique CNRS/Thales and Université Paris-Sud, France (Lee C. Phillips; Vincent Garcia; Stephane Fusil; Edouard Lesne; Eric Jacquet; Manuel Bibes; Agnes Barthelemy) Laboratoire SPMS, UMR8580, CNRS-CentraleSupélec, Université Paris-Saclay, France (Pascale Gemeiner; Brahim Dkhil)

Resume : Oxide thin films possess diverse functionalities [1] but are sensitive to small variations in defects and microstructure, an important challenge for applications. In ferroelectrics, defect doping antagonizes ferroelectricity and causes imprint and leakage. As the common research tool, pulsed laser deposition (PLD), is very sensitive to parameter tuning, and common characterization techniques provide only limited defect information, there is a great need to improve microstructural characterization standards. Here we use use Raman spectroscopy with ultraviolet (UV) excitation to evaluate strained epitaxial films of the prototypical ferroelectric BaTiO3 (BTO) that exhibits tunnel electroresistance [2], memristive effects [3] and control of spin polarization [4]. UV-Raman is a rapid, non-destructive and cost-effective technique that probes modes associated with ferroelectricity, and is critically sensitive to the defect environment. UV-Raman signatures are correlated with growth mode, functional behaviour and tunneling electroresistance. Our work should improve reproducibility and optimize functionality in thin film ferroelectrics for research and technological applications. This work was supported by the French ANR project NOMILOPS (ANR-11-BS10-0016), and ERC Advanced Grant FEMMES (contract n°267579). [1] Bibes et al. Adv. Phys. 60,5 (2011) [2] Garcia et al. Nature 460, 81 (2009) [3] Chanthbouala et al. Nature Mater. 11, 860 (2012) [4] Garcia et al. Science 327, 1106 (2010)

Authors : C . Kadlec, V. Skoromets, and P. Kužel
Affiliations : Institute of Physics, AS CR, Na Slovance 2, 18221 Prague 8, Czech Republic

Resume : For several years, we have studied the possibility to electrically modulate the propagation of terahertz (THz) radiation using SrTiO3 (STO) strained thin films [1,2]. Indeed, the dielectric behavior of STO is controlled by the soft mode whose frequency depends on temperature and electric field. Tensile strain in STO films grown on a DyScO3 (DSO) substrate enables one to induce the ferroelectric phase transition close to room temperature [3]. DSO layers are intercalated between the STO ones to maintain the strain. With this further work, a deeper understanding of the physics of strained STO thin films has been reached [4]. A tunable structure suitable for applications is proposed. The dependence of the dielectric spectra on temperature and external electric field is described by a general model which involves a damped harmonic oscillator (soft mode) coupled to a Debye relaxation (central mode). Near the phase transition, the relaxation is silent and observable in the spectra only owing to its coupling to the polar soft mode. At lower temperatures, the soft mode hardens and exerts less influence on the THz dynamics. In contrast, the central mode becomes stronger and, under 120 K, it mainly determines the shape of the measured spectra.

Authors : R. Moalla1, B. Vilquin1, G. Saint-Girons1, N. Baboux2, G. Sebald3, R. Bachelet1
Affiliations : 1 INL-CNRS, Ecole Centrale de Lyon, Ecully, France 2 INL-CNRS, INSA de Lyon, Villeurbanne, France 3 LGEF, INSA de Lyon, Villeurbanne, France

Resume : Electrocaloric (EC) materials, which couple a change in temperature with an applied electric field, can address cooling applications in microelectronic systems and are subject of growing interest [1,2]. Ferroelectric oxides as PZT films appear as good candidates for this purpose [3]. However, in spite of the growing number of EC studies on pyroelectric oxides, their structure-properties relationships are still missing. In this communication, we will show the impact of the domain-orientation on the ferroelectric and EC properties of epitaxial PbZr0.52Ti0.48O3 (PZT) films. The main domain-orientation is tuned here by the thermal expansion mismatch with the substrate. SrTiO3(001) and Si(001) substrates are used to generate different orientations of the ferroelectric domains: mainly c-axis and a-axis, respectively. The EC effect is revealed to be much larger along the polarization axis and temperature changes can reach 12°C in c-oriented PZT films near room temperature under 900 kV/cm in comparison to 5°C in a-oriented, in the same conditions. This tendency is similar to what has been observed for intrinsic pyroelectric coefficients [4]. These results are of high interest for refrigeration applications, thermal energy harvesting or thermal sensing applications in integrated systems. [1] G. Sebald et al., J. Appl. Phys. 100, 124112 (2006) [2] J.F. Scott, Annu. Rev. Mater. Res. 41, 229 (2011) [3] E. Defay et al., Adv. Mat. 25, 3337 (2013) [4] R. Moalla et al., submitted

18:00 Best Student Presentation Awards Ceremony and Reception (Main Hall)    

No abstract for this day

Symposium organizers
Mael GUENNOUCRP Gabriel Lippmann

41 rue du Brill 4422 Belvaux Luxembourg

+352 470 261 512
Krystian ROLEDERInstitute of Physics | University of Silesia

Uniwersytecka 4 40-007 Katowice Poland

+48 32 359 1478
Brahim DKHILEcole Centrale Paris Laboratoire SPMS, ECP

Grande voie des vignes 92290 Chatenay-Malabry France

+33 1 41 13 15 86
Jiří HLINKAInstitute of Physics | Czech Acad. Sci.

Na Slovance 2 182 21 Prague 8 Czech Republic

+420 266 05 2 154