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2014 Fall Meeting

OXIDE MATERIALS

V

Functional perovskite systems

Multifunctional perovskite-type oxides and systems based thereon enable numerous device applications in electronics, sensing, energy and health sectors. The symposium will focus on experimental and theoretical advances in obtaining and understanding novel or enhanced properties of perovskites for emerging or improved devices.

Scope

Perovskite-type oxides are known to exhibit a full spectrum of electronic properties - from insulating to semiconducting, metallic, and superconducting - and possess ordering of magnetic spins or electric dipoles, or both. Among the best known perovskites are ferroelectrics, high-temperature superconductors, colossal magnetoresistive oxides, Mott insulators, and multiferroics. Their high sensitivity to external fields, as well as the variety of effects and couplings that they present, make many of these materials multifunctional and enable numerous device applications. Progress in the synthesis of perovskite crystals, thin films, multilayers, and nanostructures makes it possible to create systems with completely novel or enhanced functions allowing for conceptually new devices. Their application areas include microelectronics and information storage, sensors, actuators, acoustical transducers, high-frequency and micromechanical devices, solid-state coolers, devices for energy conversion, and many others in the electronics, energy and health sectors.

The spectacular variation in behavior of perovskites is mainly related to the large effects on electronic structure and ferroic order parameters caused by small changes in their chemical composition and atomic structure. Response functions of perovskites also depend on properties of phase boundaries such as domain walls, surfaces, or interfaces. Susceptibility of the atomic and electronic structures to external magnetic, electric, stress, and light fields contribute to multifunctional behaviour too. Additionally, latent heat of phase transitions under applied fields offers more functions. A fundamental understanding of the crystal structure, electronic structure and electronic processes, phase boundaries and phase transformations, is at the heart of the developments to design perovskite systems with enhanced or novel functions able to lead to application breakthroughs.

The symposium will be an interdisciplinary forum for researchers working on perovskite-based systems. It will bring together experimental and theoretical physicists, chemists, and material scientists working on both fundamental aspects and device applications. The recent advances, challenges, and foreseen future developments will be discussed.

Hot topics to be covered by the symposium

  • Crystal structure of advanced perovskite systems
  • Electronic structure and processes
  • Optical properties
  • Phase boundaries
  • Phase transformations 

List of invited speakers

  • M. Alexe (UK): Photoelectric effects in non-centrosymmetric materials
  • U. Aschauer (Switzerland): Strain-defect interaction in oxides
  • A. Bokov (Canada): Relaxor behavior of disordered perovskites
  • G. Catalan (Spain): Metal insulator transitions in perovskite systems
  • B. Dkhil(France): How relaxors can benefit from the other physics
  • M. Fiebig (Switzerland): Domain walls in multiferroics as functional interfaces
  • V. Fiorentini (Italy): Layered perovskites as a playground for multiferroicity and beyond
  • J. Fontcuberta (Spain): Electronic reconstructions at oxide surfaces and interfaces
  • Ph. Ghosez (Belgium): Oxide heterostructures and large-scale simulations
  • J. Kreisel (Luxemburg): Multiple structures and polarization rotation in bismuth-based perovskite
  • A. Levanyuk (Spain): Phase transitions and domains in ferroelectric thin films and multilayers
  • R. Mankowsky (Germany): Time-resolved studies of complex oxides
  • B. Noheda (The Netherlands): Controlling domains and domains walls at the nanoscale
  • S. Pennycook (USA): Probing functional perovskites through scanning transmission electron microscopy and first-principles theory
  • L. Pintilie (Romania): Pyroelectric and photovoltaic properties of ferroelectric thin films
  • R. Poprawski (Poland): Synthesis of novel composites
  • E. Salje (UK): Structural and functional domain boundaries
  • A. Tagantsev (Switzerland): Charged domain walls: experiment and understanding
  • Z.G. Ye (Canada): Phase transitions, domain structures and local instabilities in PZT crystals
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11:45
Authors : J.E. Rault, O. Mentes, A. Locatelli, N. Barrett
Affiliations : Synchrotron-SOLEIL, BP 48, Saint-Aubin, F91192 Gif sur Yvette CEDEX, France; Sincrotrone Elettra - Sincrotrone Trieste S.C.p.A., AREA Science Park 34149 Basovizza, Trieste, Italy; CEA, DSM/IRAMIS/SPEC, F-91191 Gif-sur-Yvette Cedex, France

Resume : The switchable bipolar ground state is at the heart of research into ferroelectrics for future, low-energy electronics. Polarization switching by an applied field is a complex phenomenon which depends on the initial domain ordering, defect concentration, electrical boundary conditions and charge screening. Injected free charge may also to be used to reversibly switch in-plane polarized domains. We have shown that a very low energy electron beam can reversibly switch in-plane polarization of single crystal BaTiO3. Using a low energy electron microscope we can simultaneously switch and image the in-plane domain polarization. Switching proceeds by propagation of needle domains along the polar direction and then sidewall expansion to complete the polarization switch within the domain. We suggest that the injected charge destabilizes the polarization charge at domain walls, switching the polarization whilst preserving the ferroelastic domain pattern. The current density required to switch the in-plane polarization is 0.26 mA/cm2. This scales to 1 pA for a 10 x 3 microns domain. Fine tuning of the electron energy may also allow to increase the switching speed by orders of magnitude. One could imagine low power opto-electronic devices based on such phenomena.

V.2..3
12:00
Authors : E.K.H. Salje
Affiliations : University of Cambridge

Resume : Functional interfaces are at the core of research in the emerging field of "domain boundary engineering" where polar, conducting, chiral and other interfaces and twin boundaries have been discovered. Ferroelectricity was found in twin walls of paraelectric CaTiO3. We show that the effect of functional interfaces can be optimized if the number of twin boundaries is increased in densely twinned materials. Vortex structures exist in twin boundaries of SrTiO3; the switching of ferroelectric vortices is discussed.

V.2..4
15:00
Authors : Stanislav Kamba1, Veronica Goian1, Rainer Held2, Nathan Orloff,3 James C. Booth,4 Che-Hui Lee2, Alexander Melville2, Eric Bousquet5, and Darrell G. Schlom2,6
Affiliations : 1Institute of Physics, ASCR, Na Slovance 2, 182 21 Prague, Czech Republic; 2Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853, USA 3Department of Physics, University of Maryland, College Park, Maryland 20742 USA 4National Institute of Standards and Technology, Boulder, Colorado 80305, USA; 5Physique Théorique des Matériaux, Université de Liège, B-4000 Sart Tilman, Belgium; 6Kavli Institute at Cornell for Nanoscale Science, Ithaca, New York 14853, USA

Resume : Already in 2004, it was experimentally demonstrated that 1% epitaxial strain can induce ferroelectric order in thin films of SrTiO3 near room temperature. Lowest-frequency polar phonon is highly sensitive on external electric field and therefore permittivity is well tunable by electric field in microwave and THz region. Unfortunately, high microwave dielectric loss does not allow any application of this tunability. Very recently, we demonstrated that ~ 1% tensile strain induces ferroelectric phase transition also in incipient ferroelectric Srn+1TinO3n+1 (n=1-6) crystallizing in Ruddlesden-Popper structure. Tc increases with n and reaches 180 K in Sr7Ti6O19 film. Simultaneously, the n=6 film exhibits high tunability and exceptionally low dielectric loss at 300 K that rivals all known tunable microwave dielectrics. During my talk, I will explain the origin of the low loss and high tunability. In 2010, we have demonstrated that biaxial strain can induce the ferroelectric and ferromagnetic state in epitaxial thin films of EuTiO3, a material that is paraelectric and antiferromagnetic in the bulk. We found that 1% tensile strain in EuTiO3/DyScO3 induces ferroelectricity at 250 K and ferromagnetism at 4.2 K. Higher critical ferroelectric and ferromagnetic temperatures were predicted from first principles in strained EuO and SrMnO3 thin films. Results of our very recent investigations performed on these films will be presented.

V.3..4
16:30
Authors : B. Dabrowski1, J. Mais1, O. Chmaissem1, S. Kolesnik1, E. Markiewicz2, V. Goian3, S. Kamba3, and J. Lynn4
Affiliations : 1Deptment of Physics, Northern Illinois University, DeKalb, IL, USA; 2Institute of Molecular Physics, Polish Academy of Sciences, Poznan, Poland; 3Institute of Physics, Academy of Sciences of the Czech Republic; 4NIST Center for Neutron Research, Gaithersburg, MD, USA

Resume : We have prepared unique 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 cations. Similar to Ba2+Ti4+O3, the classical displacive-type ferroelectric phase transition occurs for x > 0.4 when the Mn ions move out of the center of the MnO6 octahedral units. These materials show on cooling a sequence of transitions from the paramagnetic and paraelectric cubic phase to the paramagnetic and ferroelectric tetragonal P4mm phase and finally to antiferromagnetic and paraelectric cubic (x<0.44) or P4/mmm phase (x>0.44). The largest known magneto-electric coupling was observed near TN when ferroelectricity disappears. Because of high conductivity the measurements of complex dielectric permittivity are reliable only below 40 K, where intrinsic permittivity is about 340 and does not change with magnetic field up to 9 T. Microwave measurements reveal giant extrinsic permittivity due to conductivity of the samples. No clear anomaly, which could be explained by ferroelectric phase transition was observed. The antiferromagnetic order parameter has energy gap of 4.6(5) meV and the top of the magnon band at 43(1) meV. Nearest-neighbor exchange modeling indicates exchange constant of J=4.8(2) meV.

V.4..2
17:00
Authors : Ryszard Poprawski
Affiliations : Institute of Physics Wrocław University of Technology Wybrzeże Stanisława Wyspiańskiego 27 50–370 Wroclaw Poland

Resume : Multiferroic materials with concurrent ferromagnetic and ferroelectric properties offer a possibility of a control of electric properties with the magnetic field and magnetic properties with the electric field. The materials can be employed in sensors, transducers and four-stage elements of non-volatile memories. This is why these materials are extensively investigated in research and industrial centers. So far a single-phase multiferroic material has not been found with interesting properties at room temperature. For that reason profound studies on multiphase materials are carried out (layered structures or columnar structures). Our investigation is focused on three-phase ferroelectric nanocomposites obtained on a basis of magnetic porous glasses. Two-phase sodium-boron-silica glasses doped with iron oxides are the starting material. The phase separation occurs on heating at a certain temperature. An unstable sodium-boron phase is etched with HCl and silica gel remaining in pores is washed out with KOH. Such glasses are characterized with a narrow distributions of the pore sizes, and then various kinds of ferroelectrics are introduced into the glasses. Multiferroic nanocomposites obtained on a basis of porous glasses possess very low electric conductivity which renders studies of dielectric properties and the spontaneous polarization possible. The obtained nanocomposites showed both ferromagnetic and ferroelectric properties in a wide temperature range as was demonstrat.

V.4..4
 
Poster Session I : -
17:30
Authors : Pavel V. Krasovskii
Affiliations : Baikov Institute of Metallurgy and Materials Science, Moscow

Resume : Knowledge of the oxygen content is of significant importance for the characterization of functional oxide ceramics both in research and process control. The aim of this work was to evaluate the accuracy of the measurement of the oxygen content of oxides using carrier gas hot extraction method (CGHE). The study was motivated by the improved high oxygen analytical capabilities of the state of the art instrumentation for CGHE method (LECO corp., USA). The procedure involved the decomposition of the oxide sample (5 – 50 mg) inside a double-walled graphite capsule with Ni and Sn flux by impulse heating up to 2500 – 3000 K under flowing helium gas. Oxygen evolved was detected as CO and CO2 by non-dispersive infrared cells. The focus was on building a proper calibration model for simultaneous CO/CO2 detection. The series of the cross-check calibration experiments was performed with a set of pure reference oxides, including NiO solid reference material (SRM) with certified oxygen content (BAM, Germany). The expanded uncertainty on the measurement of the oxygen content was estimated to be equal to ca. 0.1 mass.% over the working range 2 – 15 mg O. Using multiple reference sample approach, the expanded uncertainty could be reduced to ca. 0.05 mass.%. The investigation of the step-wise decomposition of rare-earth oxide samples under ramp heating conditions was demonstrated as well.

V.V I.1
17:30
Authors : A. Dejneka1, V. Trepakov1,2, L. Jastrabik1, A. Lynnyk1, P. Syrnikov2, P. Markovin2, M. Tjunina1,3
Affiliations : 1Institute of Physics ASCR, 182 21 Prague 8, Czech Republic; 2Ioffe Physical-Technical Institute of the RAS, 194 021 St.-Petersburg, Russia; 3 Microelectronics and Materials Physics Laboratories, University of Oulu, P.O. Box 4500, 90014 Oulun yliopisto, Finland

Resume : Potassium tantalate KTaO3 (KTO) is a quantum paraelectric, which has been widely investigated as a model of ABO3 perovskite-structure ferroelectrics. Despite decades of research, knowledge of band structure, electronic interband transitions, and temperature evolution of the related optical properties of this wide bandgap material remains controversial and incomplete. In particular, the index of refraction in the transparency range increases on cooling in KTO that is on contrary to the behavior in other ionic crystals and semiconductors. The physical mechanism of such an anomalous negative thermo-optics in KTO is unclear. In attempt to elucidate this mechanism, experimental studies of optical constants as a function of photon energy (1 – 6 eV) and temperature (4.2 – 300 K) are performed in single-crystal KTO. The measurements are carried out using variable angle spectroscopic ellipsometry. The optical transitions in vicinity of the absorption edge are inspected carefully. The absorption edge and the indirect transitions are found to shift to higher energies on cooling. At the same time, an increase of absorption in the spectral region of the direct G15 -G25 transitions (around 4.1 - 4.6 eV) is observed. The negative thermo-optical behavior is a consequence of these coexisting phenomena. Their microscopic nature requires further studies

V.V I.6
17:30
Authors : I. Jankowska-Sumara1, A. Majchrowski2
Affiliations : 1Institute of Physics, Pedagogical University of Cracow, ul. Podchorążych 2, Kraków, Poland 2 Institute of Applied Physics, Military University of Technology, ul. Kaliskiego 2, Warszawa, Poland

Resume : The effect of Sn substitution on the antiferroelectric phase transitions in PbHfO3 single crystals doped with small amount of Sn, from the point of view of dielectric, optic and thermodynamic measurements was studied. Dielectric and thermodynamic measurements were performed mainly in order to characterise the phase transitions sequence in PbHfO3:Sn crystals. The temperatures and orders of particular phase transitions have been determined and compared. The first order character of the phase transitions in PbHfO3:Sn was than discussed. Dielectric dispersion measurements were performed in the frequency range from 20 Hz to 2 MHz. The observed effects for PbHfO3:Sn crystals were compared and discussed with previously investigated low frequency dielectric relaxation observed in antiferroelectric PbHfO3 single crystal in paraelectric phase as well as below TC. A characteristic feature is the existence of local maximum on '(T) dependence close to TC both on heating and on cooling. Distinct dielectric dispersion was observed in this region. I case of the optic studies, temperature changes of domain structure and linear birefringence was measured by means of polarizing microscope. A very thin transient phase just below Tc was found to exist.

V.V I.9
17:30
Authors : J. Schwarzkopf, D. Braun, A. Kwasniewski, P. Müller, M. Schmidbauer
Affiliations : Leibniz-Institute for Crystal Growth, Max-Born-Str. 2, 12489 Berlin, Germany

Resume : Formation of ferroelectric domains in thin oxide films have large impact on the ferro- and piezoelectric properties of thin films and can systematically be influenced by the growth of epitaxially strained thin films on lattice mismatched substrates. In this study, thin films of KxNa1-xNbO3, which exhibits promising piezoelectric properties as bulk material, were grown by the liquid-delivery spin metal-organic chemical vapor deposition method. Understanding and controlling of domain formation is achieved by the variation of the film composition (x = 0 – 0.9) and the application of different oxide substrates. Our results clearly indicate that the alignment of the ferroelectric domains and thus the polarization vector strongly depends on the choice of the substrates. While films under tensile lattice strain exhibit regularly arranged a1a2 domains with an exclusive in-plane alignment of the polarization vector, with increasing compressive lattice strain an enhanced out-of-plane component of the polarization vector develops resulting in the sequence of multidomains of a1a2-->a1a2/c-->MB-->MA-->MC. For K0.75Na0.25NbO3 thin films on SrTiO3 substrates we have observed essentially show small, irregular arranged domains with large in-plane and out-of-plane piezoresponse. Decay of the piezoresponse signal after poling as a function of time is well described by the Kohlrausch-Williams-Watts (KWW) relaxation function with $beta$ = 0.4, which indicates relaxor behavior.

V.V I.11
17:30
Authors : A.A. Tikhii, V.A. Gritskih, S.V. Kara-Murza, N.V. Korchikova, Yu.M. Nikolaenko, I.V. Zhikharev
Affiliations : Lugansk National Taras Shevchenko University, 91011 Lugansk, Ukraine; Lugansk National Taras Shevchenko University, 91011 Lugansk, Ukraine; Lugansk National Taras Shevchenko University, 91011 Lugansk, Ukraine; Lugansk National Taras Shevchenko University, 91011 Lugansk, Ukraine; Donetsk Institute for Physics and Engineering named after O.O. Galkin, 83114 Donetsk, Ukraine; Donetsk Institute for Physics and Engineering named after O.O. Galkin, 83114 Donetsk, Ukraine

Resume : We propose a semi-empirical method for estimating the oxygen deficiency δ of La0.7Sr0.3MnO3-δ (LSMO) films obtained by dc magnetron sputtering of ceramic target. The method is based on a comparison of the calculated oxygen deficiency dependence of the refractive index with the experimental value of refractive index of the films. Calculation of the refraction index was performed using molecular ionic and crystalline valence refractions and takes into account the screening effect of the charge carriers directly associated with oxygen deficiency. The refractive index, thickness and conductivity of LSMO-films were determined by multi-angle reflectivity ellipsometry at the wavelength of the He-Ne laser (632.8 nm) after preparation and after annealing. Comparison of the oxygen deficiency in the control sample before and after annealing shows good agreement with the corresponding results obtained by an independent method. Annealing brings the composition of the all investigated epitaxial and polycrystalline LSMO-films to stoichiometric one with refractive index in the range 1.87-1.9 [1, 2]. 1. A. Tikhii, V. Gritskih, S. Kara-Murza, N. Korchikova, Yu. Nikolaenko, and I. Zhikharev. Phys. Status Solidi C 10, 673 (2013). 2. V.N. Varyukhin, Yu.V. Medvedev, Yu.M. Nikolaenko, A.B. Mukhin, B.V. Belyaev, V.A. Gritskikh, I.V. Zhikharev, S.V. Kara-Murza, N.V. Korchikova, A.A. Tikhii. Technical Physics Letters 35, Issue 10, pp 937-940 (2009).

V.V I.12
17:30
Authors : Michał Pilch, Andrzej Molak
Affiliations : Institute of Physics, Uniwersity of Silesia, 40-007 Katowice, Poland

Resume : Resistance switching effect has been studied in NaNbO3:Mn crystals. Samples were rejuvenated in ambient air, below and above antiferroelectric phase transition. Dielectric spectroscopy has exhibited weak dispersion in dielectric permittivity. Influence of the annealing on electronic structure has been determined with use of X-ray photoelectron spectroscopy. The Na 2s, Nb 3d, O 1s, and Mn 2p lines of the aged as-grown crystal and the rejuvenated samples spectra have been analyzed. Occurrence of Nb4+ state indicates occurrence of oxygen vacancies in surface layer. The Na ions migrate toward surface due to rejuvenation. Direct current resistance RDC has been measured in 300-550 K range. We have observed switching from insulator high resistance state to semiconductor medium resistance, and finally to metallic-type low resistance state. The results are discussed in framework of the extended defects model. We propose that the aliovalent Mn2+ dopant ions stabilize oxygen vacancies and enable the resistive switching.

V.V I.14
17:30
Authors : J. Kaczkowski, M. Pugaczowa-Michalska, A. Jezierski
Affiliations : Institute of Molecular Physics, Polish Academy of Sciences, ul. M. Smoluchowskiego 17, 60-179 Poznan, Poland

Resume : The electronic structure of different phases of BiFeO3 were calculated by using density functional theory (DFT). The DFT+U and semilocal Tran-Blaha modified Becke-Johnson (TB-mBJ) potential were used. DFT+U results are in good agreement with previous calculations. Our results have shown that in case of R3c, Pnma, Pn21a BiFeO3 has G-AFM ordering and C-AFM in case of Cm space group. In all calculated structures BiFeO3 is a semiconductor with the band gap: 2.26 eV (2.27 eV) for R3c, 1.91 eV (1.66 eV) for Pnma, 1.99 eV (2.18 eV) for Pn21a and 2.09 eV (2.55 eV) for Cm within DFT+U (TB-mBJ). This work was supported by the National Science Centre (Poland) through Grant nr DEC-2011/01/B/ST3/02212

V.V I.16
17:30
Authors : A. Iljinas, V. Stankus, B. Abakevičienė, J. Čyvienė
Affiliations : Kaunas University of Technology, Studentu 50, LT-51368 Kaunas, Lithuania

Resume : One of important perovskite structure material are lead titanate (PbTiO3). Thin films has great importance for high technology devices as ferroelectric random access memory (FRAM), pyroelectric infrared detectors, piezoelectric properties and other. The main problems of fabrication of such thin films is a high temperatures (500-700oC), stoichiometry, which leads to mixtures of different oxide’s phases (Pb, PbO, TiO2 and PbTiO3, Pb2Ti2O6). It is very difficult to form flat structures. Pb are very volatile at high temperatures, therefore many methods use ex-situ or post annealing methods. But thin films, formed by many ex-situ technologies are nonquality (porous, grained and rough). Our proposed method is to form PbTiO3 thin films by deposition of multilayers (~1 nm) of single oxides, sputtered by reactive magnetron deposition method on thermal heated (550 oC, 600 oC, 650 oC and 700oC) substrate (in-situ). Substrates were silicon and platinized silicon. Structure changes, phase composition of as deposited thin films were measured and analyzed using X-ray diffraction method. The surface morphology was investigated by SEM microscopy. Hysteresis loop was measured and dielectric properties were analyzed by impedance spectroscopy method.

V.V I.24
17:30
Authors : Laura Bégon-Lours, Rozenn Bernard, Eric Jacquet, Cécile Carretero, Karim Bouzehouane, Stephane Fusil, Vincent Garcia, Stephane Xavier, Stephanie Girod, Cyrile Deranlot, Manuel Bibes, Agnès Barthélémy & Javier E. Villegas.
Affiliations : Unité Mixte de Physique CNRS-Thalès (UMR137), 1 av. A. Fresnel, 91767 Palaiseau Cedex, France

Resume : We measured vertical transport across superconductor/ferroelectric/normal-metal junctions, to investigate electroresistance effects induced by ferroelectric switching. Ultrathin (4 to 8 nm thick) manganese-doped bismuth ferrite (BiFeO3-Mn) is deposited by Pulsed Laser Deposition on top of 50 nm thick superconducting YBaCuO3 films. Nano and microscale junctions are then defined using a series of nanofabrication steps which include e-beam lithography, metal deposition (Nb or Co capped with Pt) and lift-off. Conductive-Tip Atomic Force Microscopy and Piezoresponse Force Microscopy are performed to measure the junction’s electroresistance. The amplitude of this effect and the ferroelectric coercive fields are measured at room temperature as well as below the critical temperature of YBaCuO3. The observed behavior will be compared with that of ordinary ferroelectric junctions. Work supported by DIM Oxymore

V.V I.28
17:30
Authors : J. Hlinka1, T. Ostapchuk1, E. Buixaderas1, C. Kadlec1, P. Kuzel1, I. Gregora1, J. Kroupa1, M. Savinov1, J. Petzelt1, J. Drahokoupil1, and J. Dec2
Affiliations : 1Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, Prague 8, Czech Republic, CZ-182 21 2Institute of Materials Science, University of Silesia, Bankowa 12, Katowice, Poland, PL-40-007

Resume : PbZrO3 is a model example of an antiferroelectric (AFE) oxide. Its phase transition from the cubic phase (Z=1) to the orthorhombic AFE one (Z=8) is the result of the condensation of two order parameters at the wave vectors Q1 = (0:25; 0:25; 0) and Q2 = (0:5; 0:5; 0:5). Due to the huge multiplication of the unit cell, a large number of phonon modes becomes active in the infrared and Raman spectra of the AFE phase. These modes have been identified in our recent spectroscopic studies of PbZrO3 single crystals. Our data allowed to relate these optically active modes to the phonon modes at special Brillouin zone points of the parent, high temperature cubic phase (at Brillouin zone points Q1 and Q2, for example) [1]. Since there are no direct experimental measurements of phonon dispersion curves available so far, we tried to reconstruct some of them from our data, as often done for incommensurate dielectrics. Our measurements revealed a strong anisotropy of the low-frequency dielectric constant and softening of phonons of seven different symmetries. This last result can be understood by the presence of a whole soft and flat phonon branch, which guarantees a simultaneous instability with respect to both the homogeneous and the staggered polarization. From these results, we deduce that the AFE phase in PbZrO¬3 is stabilized by a trilinear coupling term. Support by the Czech Science Foundation is acknowledged (Project 13-15110S). [1] J. Hlinka et al., Phys. Rev. Lett 112, 197601 (2014)

V.V I.33
Start atSubject View AllNum.
 
Session I : FILMS 1
Chair: M. Alexe
09:00
Authors : Qi Hang Qin (1), Laura Äkäslompolo (1), Lide Yao (1), Sayani Majumdar (1), Jaianth Vijayakumar (1), Slawomir Zietek (2), Ilona Pohjavirta (1), Pekka Kupiainen (1), Jaroslaw Kanak (2), Tomasz Stobiecki (2), and Sebastiaan van Dijken (1)
Affiliations : (1) Department of Applied Physics, Aalto University School of Science, FI-00076 Aalto, Finland (2) Department of Electronics, AGH University of Science and Technology, 30-059 Kraków, Poland

Resume : Ferroelectric tunnel junctions (FTJs) have opened up promising routes towards energy-efficient data storage applications and memristive devices. Polarization reversal in a ferroelectric tunnel barrier can change the resistance of a junction, an effect known as tunneling electroresistance (TER). Large TER has been obtained for junctions that are comprised of different electrodes. Here, we demonstrate that a giant TER effect of 10 000 000% can be realized in nominally symmetric junctions of two La2/3Sr1/3MnO3 (LSMO) electrodes separated by a PbZr0.2Ti0.8O3 (PZT) or BaTiO3 (BTO) tunnel barrier. The TER is ascribed to structural dissimilarities at the barrier/electrode interfaces and their influence on a polarization-induced metal-to-insulator transition in LSMO. Evidence for this scenario is obtained from transmission electron microscopy and in-plane electric transport measurements inside a piezo-response force microscope. From these data, it is estimated that a 0.8 nm thick LSMO interface layer becomes insulating when the polarization of the ferroelectric barrier points towards the bottom electrode. This effect increases the tunnel barrier width and it enhances the tunnel barrier resistance. A similar effect does not occur when the polarization points to the LSMO top electrode due to roughness and atomic mixing at the interface. The robust TER response indicates that interface engineering of FTJs provides a viable scheme for the design of sensitive resistive switching devices.

V.5.1
10:00
Authors : Lide Yao, Sayani Majumdar, Laura Äkäslompolo, Sampo Inkinen, Qi Hang Qin, and Sebastiaan van Dijken
Affiliations : NanoSpin, Department of Applied Physics, Aalto University School of Science, FI-00076 Aalto, Finland

Resume : Transition metal oxides with a perovskite crystal lattice of type ABO3 may possess corresponding oxygen-deficient modulation structures with different material properties. One prototypical example is the brownmillerite structure of type ABO2.5, which due to its high ionic conductivity could find applications in solid oxide fuel cells, oxygen-separation membranes, and gas sensors. Here, we demonstrate that the evolution of the perovskite-brownmillerite phase transition can be fully controlled and monitored in epitaxial La2/3Sr1/3MnO3 (LSMO) films using electron-beam irradiation in a transmission electron microscope (TEM). Real-time TEM imaging with atomic resolution reveals that the structural transition is driven by an incessant ordering of electron-beam induced oxygen vacancies in every second MnOx plane. The local depletion of oxygen reduces the coordination of Mn cations, causing a vertical displacement of the La/Sr ions. Over-irradiation of the brownmillerite phase induces a second transition to a perovskite-like structure with disordered oxygen vacancies and an enhanced out-of-plane lattice compared to the original LSMO film. Electron energy loss spectroscopy and energy-dispersive x-ray spectroscopy confirm the findings. The demonstrated ability to simultaneously induce and characterize oxygen-deficient structural phases in a continuous and controllable manner opens up new pathways for atomic-scale studies on electronic and ionic transport in complex oxide materials.

V.5.4
11:30
Authors : M. Scigaj [1,2], J. Gazquez [1], M. Varela [3,4], J. Fontcuberta [1], G. Herranz [1], and F. Sánchez [1]
Affiliations : [1] Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus de la UAB, Bellaterra 08193, Spain; [2] Dep. de Física, Universitat Autònoma de Barcelona, Campus de la UAB, Bellaterra 08193, Spain; [3] Dpt. Física Aplicada III, Universidad Complutense de Madrid, Madrid 28040, Spain; [4] Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA

Resume : The two dimensional electron gas at the (001) interface between LaAlO3 (LAO) and SrTiO3 (STO) is generally explained considering a scenario of polar catastrophe. Remarkably, (110)- and (111)-oriented crystalline LAO/STO interfaces as well as the interface between STO(001) and some amorphous oxides can be also conducting. For the amorphous/STO interfaces, oxygen vacancies are usually claimed as the origin of the conductance. Redox reactions may depend on two factors: the oxygen affinity of the ions in the amorphous layer and the vacancy formation energy and diffusivity. Generally, the latter depends on the crystal orientation. To evaluate the relative weight of both factors, we have grown series of amorphous -LAO, YSZ and STO films on STO(110) and STO(111). The critical thickness for conduction depends on the amorphous oxide. However, it is the same for LAO/STO(110) and LAO/STO(111), strongly suggesting that differences vacancy formation energy and diffusivity are overridden by interface redox processes, which are governed by the oxygen affinity of the metal ions in the amorphous layer. TEM revealed a crystalline interfacial layer around 0.5 nm thick and EELS signaled presence of oxygen vacancies. In conclusion, the oxygen affinity of the incoming ions, rather than the crystalline plane of the substrate, is the driving force of the interface redox reactions that triggers conduction at amorphous/STO interfaces.

V.6.2
14:30
Authors : Pintilie Lucian, Alin Iuga, Cristina Chirila, Mihaela Botea, Lucian Trupina, Ioana Pintilie, Andra Georgia Boni, Luminita Hrib
Affiliations : National institute of Materials Physics, Atomistilor 105 bis, Magurele, Romania

Resume : Results regarding the pyroelectric and photovoltaic properties of the ferroelectric thin films will be presented. The main parts will be: - growth of good quality epitaxial ferroelectric films and preliminary structural/electrical characterization - short-circuit photocurrent measurements; dependence on the properties of the electrode interface; relation with the magnitude of the imprint - pyroelectric properties of epitaxial ferroelectrics - combined pyroelectric-photovoltaic properties; enhanced pyroelectric signal by continuous UV illumination - pyroelectric properties in multilayers

V.7.2
 
Session IV : PHOTOFERROELECTRICS
Chair: L. Pintilie
16:00
Authors : Marin Alexe, Akash Bhatnagar
Affiliations : University of Warwick, Department of Physics, CV4 7AL Coventry, UK

Resume : In the recent past, the field of photo-ferroelectrics has been revitalized by the reports of photovoltaic effect (PVE) in BiFeO3 (BFO). Unlike traditional semiconductors the open circuit voltages in these materials are not limited by band gap Eg, they can exceed Eg by orders of magnitude. The microscopic origins of this effect are still under debate. Initial investigations on BFO films assumed that the PVE in BFO is primarily due to the presence of a potential step at the domain wall. However, in our recent work it was observed that the generation and recombination of photo-generated non-equilibrium carriers are primarily affected by the presence of shallow energy levels and the anomalous bulk photovoltaic effect play the major role in PVE. This talk will address fundamentals of photoferroelectrics and anomalous bulk photovoltaic effect in BiFeO3. Besides of that, newly characterization methods based on local photoelectric measurement such as photo-induced transient spectroscopy (PITS) which bring valuable data regarding generation and recombination of the photo-excited carriers will be tackled. We will also discuss complementary characterization methods such as thermally stimulated current and variable temperature PV effect and show that these can provide information on electronic structure of material, respectively shallow or deep levels in the band gap, which may affect the dark and photo-conduction mechanism.

V.8.1
16:30
Authors : M. Lejman1, G. Vaudel1, I. C. Infante2, P. Gemeiner2, V. Gusev3, B. Dkhil2, P. Ruello1
Affiliations : 1. Institut des Molécules et Matériaux du Mans UMR6283 CNRS-Université du Maine, Le Mans, France 2. Laboratoire SPMS UMR8580 CNRS-Ecole Centrale Paris, Châtenay Malabry, France 3. Laboratoire d'Acoustique de l'Université du Maine UMR6613 CNRS-Université du Maine, Le Mans, France

Resume : The study of the generation of GHz-THz coherent acoustic phonons by femtosecond laser action is a powerful time-domain spectroscopy to evaluate and possibly to control the electron-phonon coupling mechanisms in solids [1]. These fundamental investigations are a key issue for future development of ultrasonic devices providing short acoustic wavelengths (nm) required for advanced nanometrology. Up to now, photo-induced GHz-THz coherent acoustic phonons have been mainly explored in metals and semiconductors as well as in artificial nanostructures [1]. However, despite their inherent strong polarization (providing natural asymmetry) and superior piezoelectric properties, ferroelectric oxides have been regarded only recently [2-5]. Here by using ultrafast pump-probe optical measurements, we report that photo-generation/photo-detection of small band-gap BiFeO3 ferroelectric leads, at room temperature, to spectacular larger GHz coherent shear acoustic wave signal (TA mode) than that coming from longitudinal mode (LA mode), as never reported in any material before [6]. The detailed analysis of the data indicates that this singular behavior comes from an efficient light-induced inverse piezoelectric mechanism. In particular, this piezoelectric effect is governed by the screening of the internal electric fields in BFO driven by light-induced charges. This giant photoacoustic response opens new perspectives for the use of ferroelectric oxides in ultrahigh frequency acoustic devices and the development of new GHz-THz acoustic sources. [1] P. Ruello, V. Gusev, Ultrasonics, Review Paper, in press (2014). [2] P. Ruello, T. Pezeril, S. Avanesyan, G. Vaudel, V. Gusev, I. C. Infante, and B. Dkhil, Appl. Phys. Lett. 100, 212906 (2012) [3] L. Y. Chen, J. C. Yang, C. W. Luo, C. W. Laing, K. H. Wu, J.-Y. Lin, T. M. Uen, J. Y. Juang, Y. H. Chu, and T. Kobayashi, Appl. Phys. Lett. 101, 041902 (2012) [4] Z. Jin, Y. Xu, Z. Zhang, X. Lin, G. Ma, Z. Cheng, and X. Wang, Appl. Phys. Lett., 101, 242902 (2012) [5] H. Wen, P. Chen, M. P. Cosgri, D. A. Walko, J. H. Lee, C. Adamo, R. D. Schaller, J. F. Ihlefeld, E. M. Dufresne, D. G. Schlom, P. G. Evans, J. W. Freeland, and Y. Li, Phys. Rev. Lett. 110, 037601 (2013) [6] M. Lejman, G. Vaudel, I. C. Infante, P. Gemeiner, V. E. Gusev, B. Dkhil, and P. Ruello, Nature Comm. in press (2014)

V.8.2
17:00
Authors : D. W. Nye1, D. S. Keeble1, S. Gorfman2, M. C. Weber3, J. Kreisel3, M. Alexe1, A. Bhatnagar4, G. Nisbet5, S.P. Collins5, P. A. Thomas1
Affiliations : 1 Department of Physics, University of Warwick, UK 2 Department of Physics, University of Siegen, Walter Flex str. 3, D57072, Siegen, Germany 3 Department "Science & Analysis of Materials (SAM)" Centre de Recherche Public Gabriel Lippmann, Luxembourg 4 Max Planck Institute of Microstructure Physics, D-06120 Halle, Germany 5 Diamond Light Source, Didcot, UK

Resume : In a material with both a piezoelectric effect and the capability to form a photocurrent, photostriction can be observed – the deformation of the crystal by light. When studying photostriction, a potential method is to use x-rays to probe the unit cell in response to another light source as a stimulus, such as a laser or a diode. Given that x-rays are also photons it is plausible that they produce some effect in themsleves. Experiments were carried out to investigate how significant are the effects of the x-rays are in producing photostriction in the absence of any other source of illumination. The material studied in this example was bismuth iron oxide, BiFeO3. A thin film with electrodes was used, and it was found that the photocurrent generated by a laboratory x-ray source on the sample was of comparable level to that of a laser or diode used in the study of the bulk photoelectric effect. Using a novel, time dependent crystallographic approach, the intrinsic effect of synchrotron x-ray light on a photoferroelectric thin film has been investigated. Furthermore, we have simultaneously collected diffraction and photoelectric data, and the correlation between the electronic and structural properties will be discussed. These results could suggest that caution is necessary when interpreting photostriction data obtained with the use of x-rays

V.8.3
17:15
Authors : Joe Briscoe, Yongfei Cui, and Steve Dunn
Affiliations : Materials Research Institute, School of Engineering and Materials Science, Queen Mary University of London, E1 4NS, UK.

Resume : To achieve innovations in photocatalysis new materials and material types are required. Barium titanate (BaTiO3) has a similar band gap and electron affinity to TiO2, suggesting the potential for similar photocatalytic behaviour, but its perovskite structure leads to additional ferroelectric properties. We study the photocatalytic activity of BaTiO3 via the degradation of a standard organic dye molecule, rhodamine B. We compare the impact of ferroelectricity on photocatalytic activity by making use of the stability of both cubic, non-ferroelectric and tetragonal, ferroelectric BaTiO3 at room temperature. We find that a catalyst with higher ferroelectric content displays three times higher photocatalytic activity than non-ferroelectric material despite a lower surface area. In addition, photochemically depositing silver nanoparticles on the surface of the ferroelectric catalyst leads to ten times higher activity than for the non-ferroelectric equivalent. We link this enhancement to the ability of the ferroelectric material to effectively separate photoinduced charge carriers due to the polarisation-induced internal field, and the strong Stern layer formed on the ferroelectric surface, which increases dye adsorption. The further enhancement of the silver-coated catalyst is linked to preferential deposition on the positive domains, where photo-reduction is more likely to occur. This highlights the potential of ferroelectric materials for use in photocatalytic applications.

V.8.4
17:30
Authors : Thierry Pauporte and Jie Zhang
Affiliations : Institut de Recherche de ChimieParis, CNRS-Chimie ParisTech, UMR8247, 11 rue Pierre et Marie Curie, 75005 Paris, France.

Resume : The preparation of composite lead iodide perovskite/ZnO composite layers by impregnation and chemical conversion of a precursor soaking various electrochemically deposited ZnO structured films is presented. These layers have been used as photoelectrodes in excitonic solid-state solar cells with the structure: ZnO/perovskite CH3NH3PbI3/Spiro-OMeTAD. Well-conducting ZnO layers are deposited in chloride medium and grown with tailored (nano)structures ranging from arrays of nanowires to a compact, well-conducting film. Moreover, the effect of a thin intermediate overlayer of ZnO conformally electrodeposited in nitrate medium and with a low n-type doping (i-ZnO) is discussed. Our results show higher power conversion efficiencies for the nanostructured perovskite/oxide composite layers compared to the dense one. Moreover, we show that the presence of the i-ZnO layer in contact with the perovskite improves markedly the cell short circuit current and the open-circuit voltage due to charge recombination reduction. For the best cells, the active layers efficiently absorb light over a large spectral range from near-UV to near infra-red region and exhibit excellent charge collection efficiencies. Solar cells based on an optimized design generate a very large photocurrent and a power conversion efficiency above 10%.

V.V II.5
17:30
Authors : Sang Hyo Kweon, Mir Im, Sahn Nahm
Affiliations : Department of Material Science and Engineering, Korea University, Seoul, South Korea

Resume : KCa2NaNb4O13 ceramics, Dion-Jacobson layered perovskite materials, have been widely investigated because they can be easily exfoliated to the nano-sized sheets which can be used to the future multilayer capacitors with a small size and high performance. A KCa2NaNb4O13 phase was formed at 1000oC and a dense ceramics were obtained after sintering at 1325oC for 10 h. A proton exchange process was carried out to produce the intermediate phase of HCa2NaNb4O13. The stable (Ca2NaNb4O13)- nanosheet colloids were formed using the mixture of the HCa2NaNb4O13 powders, tetrabutylammonium hydroxide (TBAOH) solution and water having the same TBA+/H+ ratio. The exfoliated (Ca2NaNb4O13)- nanosheets were dispersed into the acetone medium, which was used to form the thin film by the electrophoretic method under 100 V electric source. The electrophoretic thin films were then annealed at various temperatures for 30 min under air condition and all the films have the Ca2NaNb4O13 phase. The electrical and dielectrical properties of these films will be presented in this work.

V.V II.15
17:30
Authors : Mir Im1, Sang-Hyo Kweon2, Sahn Nahm1,2
Affiliations : 1KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul 136-701, South Korea 2Department of Materials Science and Engineering, Korea University, Seoul 136-701, South Korea

Resume : Homogeneous KTiNbO5 and K3Ti5NbO14 phases were formed at 900oC and the dense KTiNbO5 and K3Ti5NbO14 oxides were obtained from the specimen sintered at 1150oC and 1125oC, respectively. Liquid-phase-assisted abnormal grain growth occurred in both specimens along the directions perpendicular to <002> during the sintering. A proton exchange process was carried out to synthesize the proton-exchanged powders which reacted with tetrabutylammonium hydroxide (TBAOH) solution and DI water to synthesize stable [TiNbO5]- and [Ti5NbO14]- nanosheet colloids. These nanosheet colloids were dispersed into the acetone, which was used to grow the thin films by the electrophoresis under 100 V electric source. The TiNbO5 and Ti5NbO14 thin-films have the (001) preferred growth direction. A high dielectric constant(εr) of 48 with a loss of 4.0% at 100 kHz was obtained from the TiNbO5 film annealed at 600oC and this film also showed a low the leakage current density of 2*10-7 A/cm2 at 0.25 MV/cm. Moreover, the Ti5NbO14 films annealed at 700oC showed an εr of 41 with a dielectric loss of 1.5 % at 100 kHz and the leakage current density of 1.5*10-7 A/cm2 at 0.3 MV/cm. Therefore, these films are good candidates for the future multilayer ceramic capator.

V.V II.16
17:30
Authors : Min-Hsiang Hsu(1,2), Marianna Pantouvaki(1), Clement Merckling(1), Joris Van Campenhout(1), Philippe Absil(1), Dries Van Thourhout(2,3)
Affiliations : (1) IMEC, Kapeldreef 75, 3001, Leuven, Belgium (2) Photonics Research Group, INTEC, Ghent University –imec, Ghent, 9000 Belgium (3) Center for Nano- and Biophotonics (NB-Photonics), Ghent University, Ghent 9000, Belgium

Resume : Monolithic integration of functional oxides on Si facilitates the progress of several novel electronics and photonics devices. BaTiO3 (BTO), with its unique opto-electrical properties, is a promising candidate for such advanced applications. Yet, the integration of BTO onto Si is very challenging due to its different crystal structure and dissimilar lattice parameter. Moreover, BTO intrinsic properties are sensitive to crystalline phases defined by stoichiometry and epitaxial conditions.This work describes the co-deposition by molecular beam epitaxy of BTO single-crystal films on Ge-on-Si(001) (GoS) pseudosubstrates. To perfectly register both BTO and Ge lattices during heteroepitxy, an in-plane 45˚ rotation of the oxide lattice with respect to Ge(001) surface has been developed using a ½-monolayer BaO at the BTO/GoS interface. Then, the impact of stoichiometry on BTO properties is studied in terms of reflection high energy electron diffraction, x-ray diffraction, transmission electron microscope, Rutherford backscattering spectroscopy and ellipsometry. Unexpectedly, we showed that epitaxial Ti-rich BTO (with high Ti/Ba>10) can still be grown on GoS with perovskite structure but with altered crystal symmetry and quality against the perfect stoichiometric BTO layers. Finally, electrical properties of epitaxial BTO films on GoS are benchmarked in function of Ba/Ti ratio, highlighting the impact of the stoichiometry on the undesirable formation of oxygen vacancies in the layers.

V.V II.19
17:30
Authors : Nekvindová P.1, Cajzl, J.1, Oswald J.2, Macková A.3, Malinský P.3, Špirková J.1
Affiliations : 1 Faculty of Chemical Technology, Institute of Chemical Technology, Prague, Czech Republic; 2Institute of Physics, Academy of Sciences of the Czech Republic, Prague, Czech Republic; 3Nuclear Physics Institute, Academy of Sciences of the Czech Republic, Rez, Czech Republic

Resume : Erbium (Er3+) is well-known for its transitions used in telecommunications systems due to the Er3+ intra-4f emission which corresponds to the 4I13/2 → 4I15/2 transition. Therefore Er3+ ions doped photonics materials are candidates for fabrication of optical amplifiers or lasers operating at 1530 nm. Lithium niobate is a very often used photonics material because of outstanding properties of its perovskite structure, which allows for modulation and amplification of the optical radiation at the same time. However, common single crystalline lithium niobate is in fact congruent crystal and real ratio of lithium to niobium is not 1:1 but about 6 % of lithium is missing. This fact enables easy doping with for instance magnesium but also, as in our case, with erbium. Doping of erbium into lithium niobate has been studied by our group for several years. In this contribution the summary of the erbium doping techniques into lithium niobate will be shown. It means that various techniques like erbium doping from metal or oxide layers, doping from melted erbium salt, erbium ion implantation, PLD and sol-gel techniques will be compared and also discussed. Possibility of erbium doping via ion implantation into other photonic crystals such as Al2O3, ZnO and diamond will be also mentioned. Properties of prepared thin films will be compared especially in terms of the erbium positions in crystal structure and luminescence properties. We acknowledge the Czech Science Foundation project GA 14-05053S. Some parts of this research were realised at the CANAM (Center of Accelerators and Nuclear Analytical Methods) infrastructure.

V.V II.22
17:30
Authors : Thierry Delahaye(1,2), Marie-H?l?ne Berger(1), Jean-Fran?ois Hochepied (1,2)
Affiliations : (1) MINES PARISTECH, University "Paris Sciences et Lettres", Center for Materials Studies, BP87 91003 EVRY cedex- FRANCE (2) ENSTA PARISTECH, Unit? Chimie et Proc?d?s, 828 Bd des Mar?chaux 91762 PALAISEAU cedex - FRANCE

Resume : Olsen cycles are able to produce electricity thanks to phase transitions between states of different polarity in pyroelectric materials. Some perovskite compounds exhibit such phase transitions in the range 80-130?C, making them attractive for conversion of waste heat into electricity. Up to now, such systems work at lab scale with thin films of pyroelectric materials sandwiched between electrodes and subjected to varying electric field and bath temperature following Olsen cycles. Based on patent WO 2011/055065, we study here a new concept of pyroelectric conversion using concentrated suspensions of submicronic particles circulating through elements of given electric fields and temperatures reproducing the Olsen cycles. If this system may be expected as less efficient per cycle as compared to solid systems, it is also much more likely to be implemented in industries. Our choice was focused in the families KNbO3-PbTiO3 (KNPT) and KNbO3-BaTiO3 (KNBT). The challenges consisted in optimizing particle size and liquid phase to get the desired charge transfer effect and stable colloidal suspensions. KNPT particles in polyols were found promising and some electrical measurements will be shown.

V.V II.23
17:30
Authors : 1) M. Wojcik, E. Jedryka, 2) D. Pesquera, F. Sanchez, G. Herranz and J. Fontcuberta
Affiliations : 1) Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02 -668 Warszawa, Poland; 2) Institute de Ciècia de Materails deBarcelona ICMAB-CSIC, Campus de la UAB, 08193 Bellaterra, Catalonia, Spain

Resume : Perovskite manganites are regarded one of the main building blocks of the oxides spintronics devices because of high spin polarization of the charge carriers and Curie point above room temperature. These properties are due to delocalization of the eg electrons in the network of 3d(Mn) and 2p(O) orbitals induced by the double exchange mechanism, leading to ferromagnetic order and metallic conductivity. However, this strongly correlated system displays a tendency to charge localization and phase separation (PS) into coexisting ferromagnetic/antiferromagnetic and metallic/insulating phases, having a detrimental impact on the magnetotrasport properties of these materials. Until now it has been accepted that in case of thin films of optimally doped La2/3Sr1/3MnO3 , phase separation takes place only within a narrow nanometrically thick dead layer close to an interface with a substrate. In this work we show that this picture is oversimplified. We have taken advantage of the extreme sensitivity of the 55Mn NMR technique to disentangle two different origins of phase separation in manganite (La2/3Sr1/3MnO3/SrTiO3) thin films. We observed that phase separation is not restricted to the dead layer at the interface, but propagates across the entire film thickness displaying a depth dependent density profile of localized holes (Mn4+). This is the evidence that the hole trapping centers located within the film volume play also an active role in PS. Moreover, from the analysis of the NMR restoring field sensed by the spins of 55Mn nuclei it has been found that these two distinct hole localization mechanisms act also as independent sources of magnetic anisotropy and their respective contribution to overall anisotropy varies across the film thickness.

V.V II.29
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Session I : FP theory 1
Chair: P. Ghosez
14:00
Authors : M. B. Maccioni, M. Scarrozza, G. M. Lopez, A. Filippetti, J. Iniguez, and V. Fiorentini
Affiliations : Physics Dept., U Cagliari; CNR-IOM Cagliari; ICMAB Barcelona

Resume : Just as their standard counterpart, layered perovskite promise to be a interesting player in the field of multiferroicity. We will discuss, based on ab initio calculations, a few examples of exotic behavior of materials in the family AnBnO3n+2x for n=4 and 5. For the insulating n=4 case, we have two examples: LaMnO3.5 is a weak ferromagnet with an anomalously large linear magnetoelectric coupling, due mainly to the soft modes involved; LaTiO3.5 doped with V is a ferromagnet, and magnetization is inverted upon polarization inversion - the quintessential magnetoelectric effect. For the n=5 case, we find that BiTiO3.41 exhibits metallic character in one space direction coexisting with non-zero polarization in an orthogonal direction, a hybrid behavior opening the way to interesting potential applications.

V.9.1
16:30
Authors : M. Guennou, J. Kreisel
Affiliations : CRP Gabriel Lippmann, Department Materials Science, Luxembourg

Resume : A growing concern regarding the toxicity in lead-containing devices, has triggered a considerable interest in lead-free piezoelectrics. Because of its electronic similarity with Pb2+, the “lone-pair” cation Bi3+ appears as a natural replacement candidate and can produce a similarly large ferroelectric polarisation. The majority of studies have focussed on only two stable materials: the multiferroic bismuth ferrite BiFeO3 with a reported strain-driven MPB in thin films, and Na0.5Bi0.5TiO3 (NBT) which presents a high piezoelectric response when doped with Ba2+. Here, we will first discuss the structural richness of Bi-based materials [1,2], before presenting in more detail the structural features of Na0.5Bi0.5TiO3 (NBT) for which we report a temperature-dependent 3D atomic-level model, which is based on a neutron pair-distribution analysis [3]. Our statistical analysis of this model shows how local distortions compete, how this competition develops with temperature and, in particular, how different polar displacements/rotations of Bi-cations coexist, highlighting the interest of Bi-based materials in the search for new lead-free piezoelectrics. [1] M. Guennou et al. Phys. Rev. Lett. 112, 075501 (2014) [2] M. Guennou et al. Phys. Rev. B 84, 174107 (2011). [3] D. S. Keeble et al. Adv. Funct. Mat. 23, 184 (2013).

V.10.2
17:15
Authors : Julita Piecha, Andrzej Molak, Christian Rodenbücher, Uwe Breuer, Krzysztof Szot,
Affiliations : Institute of Physics, University of Silesia, 40-007 Katowice, Poland; Peter Gruenberg Institut, Forschugszentrum Jülich, D-52425 Jülich, Germany; Central Institute for Engineering, Electronics and Analytics, Forschugszentrum Jülich, D-52425 Jülich, Germany;

Resume : Influence of oxidation and reduction reaction in congruent LiNbO3 monocrystals have been analyzed in macro- and nano-scale with use of surface sensitive studies. All reduced samples of lithium niobate changed their color from transparent to black. Termogravimetry measurement has been conducted in low oxygen partial pressure 10-10 mbar in range from 500°C - 1000°C. Obtained results have shown mass loss in the crystal samples. Marked decrease in mass loss has occurred at 1000°C for redox reaction. Effusion experiments carried out at 800°C and 900°C under vacuum condition allowed us to determine type of released component, i.e. lithium oxide. The LiNbO3 monocrystals, have been reduced in ultra strong condition at 950°C, 850°C, 750°C and has been analyzed with use of the Secondary Ion Mass Spectroscopy technique. The 3D profiles have shown a non homogeneous distribution of lithium and niobium elements in the matrix of the sample. Electrical measurement has been conducted at 400°C in vacuum, in macro-scale (4 point technique, allows to define resistivity dependence from bulk, anode, and cathode area, simultaneously) and nano-scale (LC-AFM). Reduction process has induced heterogenic changes of resistivity in surface layer. Topology scans show conductive nanostructures like filaments and islands. XPS measurements have shown that marked changes have been observed at the surface layer and not in the interior part of the crystal.

V.10.4
Start atSubject View AllNum.
 
Session I : FP theory 2
Chair: V. Fiorentini
09:00
Authors : Ph. Ghosez, J. Varignon, N. Bristowe, D. Fontaine and E. Bousquet
Affiliations : Theoretical Materials Physics, University of Liege, Belgium

Resume : Ferroelectricity in ABO3 perovskites and related compounds has been a topic of intensive research over the last 60 years. Recently, the coupling of the ferroelectric lattice mode with other non-polar modes has attracted an increasing interest since it offers promising and still widely unexplored possibilities to couple ferroelectricity with other functional properties and even to produce unusual phenomena. In this context, the trilinear coupling between ferroelectric and oxygen rotational modes in naturally-occuring and artificially layered perovskites emerged as a practical way to produce unusual dielectric properties or to achieve enhanced magneto-electric coupling. Focusing on vanadates and half-doped titanates, we will discuss here how even more interesting phenomena can appear when additional orbital and charge orders enter into play!

V.11.1
09:30
Authors : Julien Varignon, Nicholas C. Bristowe, Eric Bousquet, Philippe Ghosez
Affiliations : Université de Liège, Allée du 06 aout, 4000 Liège

Resume : Transition metal perovskites have attracted huge interest over the last decades since the seminal discoveries of colossal magnetoresistance and high-temperature superconductivity. Vanadium based perovskites (A3+V3+O3, A=La to Y), although not widely studied, are a fascinating playground for modern physics. These systems are Mott insulators and crystalize in the well-known Pnma phase at room temperature. With decreasing temperature, they develop “Jahn-Teller” distortions modifying the degeneracy of the d orbitals and producing different orbital-ordered phases, which can be exclusive or coexisting. Additionnaly, those orbital ordered phases are intimately connected to particular antiferromagnetic orderings. Based on a symmetry mode analysis, we identify new relevant couplings between structural, electronic and magnetic degrees of freedom in vanadates and clarify the unusual coexistence of Jahn-Teller distortions, providing new insight on the latter and their role in perovskites in general. Using first-principles calculations, these new lattice mode couplings are proven to enable an unprecented Jahn-Teller and orbital ordering induced ferroelectricity in vanadate superlattices. Finally, due to the intimate connection between orbital ordering and magnetism, an electric field control of magnetism is predicted, opening novel possibilities for the design of magnetoelectric multiferroics.

V.11.2
10:15
Authors : Jorge Iñiguez and Jacek C. Wojdel (1); Oswaldo Dieguez (1,2)
Affiliations : (1) Institut de Ciencia de Materials de Barcelona (ICMAB-CSIC), Campus UAB, 08193 Bellaterra, Spain; (2) Department of Materials Science and Engineering, Tel Aviv University, Tel Aviv 69978, Israel

Resume : Ferroelectric and ferroelastic domain walls (DWs) are becoming the focus of renewed excitement. Modern experimental techniques permit an unprecedented control on nano-domain structures, and it is now possible to produce materials with a large volume fraction occupied by the DWs themselves. Also, recent experiments show that DWs can display distinct properties not present in the domains. For example, measurements of increased conductivity and photovoltaic activity in materials like BiFeO3 suggest that the DWs could serve as active elements for applications in electronics. As a result, a lot of effort is being devoted to the engineering and optimization of the DWs. Understanding the novel DW behaviors remains a great challenge, and atomistic first-principles theory is called to play a key role in the field. We have employed a variety of tools, ranging from accurate quantum methods to approximate model potentials for large-scale simulations, to investigate DW-related phenomena. In this talk I will present some of our most striking results, including the discovery of novel structures and structural transitions at the DWs of well-known (multi)ferroic oxides, the tuning of DW properties with epitaxial strain, and ideas for inducing novel orders confined at the walls.

V.11.5
 
Session III : LEAD-BASED FERROIC CRYSTALS
Chair: B. Dkhil
14:00
Authors : Z.-G. Ye, A. A. Bokov, Y. Xie, B. Wang and X. Long
Affiliations : Department of Chemistry Simon Fraser University Burnaby, BC, V5A 1S6, Canada

Resume : PbZr1-xTixO3 (PZT) system has been extensively studied over the past decades for both industrial applications and fundamental research. Recently, PbZr1-xTixO3 single crystals with compositions (0.2 ≤ x ≤ 0.65) across the mophotropic phase boundary (MPB) region have been grown in our laboratory by a top-seeded solution growth (TSSG) technique. The availability of PZT single crystals makes it possible to systematically investigate the correlation between structural evolu-tion and electrical properties in PZT system. In this work, the domain structure and phase transitions of PZT single crystals with compositions x=0.32, x=0.42, x=0.46 and x=0.62 are studied by polarized light microscopy (PLM), piezoresponse force microscopy and dielectric measurements. PLM observation shows an in-crease of extinction angle in the two rhombohedral crystals: x=0.32 at 340 °C, and x=0.42 at 250°C, indicating a thermally induced polarization rotation accompanied with the rhombohedral (R) to monoclinic (M) phase transition. The ferroelectric to paraelectric phase transition in x=0.32 is of first order with a discontinuous change of birefringence around TC=351°C. The dielectric measurements show anomalies below TC, confirming the R-M phase transitions in both crystals. For the MPB composition x=0.46, PLM shows a monoclinic symmetry with complicated domain at room temperature, which upon heating changes to a tetragonal phase at about 286°C and then to a cubic phase at TC=394 °C. Crystals of compositioPbZr1-xTixO3 (PZT) system has been extensively studied over the past decades for both industrial applications and fundamental research. Recently, PbZr1-xTixO3 single crystals with compositions (0.2 ≤ x ≤ 0.65) across the mophotropic phase boundary (MPB) region have been grown in our laboratory by a top-seeded solution growth (TSSG) technique. The availability of PZT single crystals makes it possible to systematically investigate the correlation between structural evolu-tion and electrical properties in PZT system. In this work, the domain structure and phase transitions of PZT single crystals with compositions x=0.32, x=0.42, x=0.46 and x=0.62 are studied by polarized light microscopy (PLM), piezoresponse force microscopy and dielectric measurements. PLM observation shows an in-crease of extinction angle in the two rhombohedral crystals: x=0.32 at 340 °C, and x=0.42 at 250°C, indicating a thermally induced polarization rotation accompanied with the rhombohedral (R) to monoclinic (M) phase transition. The ferroelectric to paraelectric phase transition in x=0.32 is of first order with a discontinuous change of birefringence around TC=351°C. The dielectric measurements show anomalies below TC, confirming the R-M phase transitions in both crystals. For the MPB composition x=0.46, PLM shows a monoclinic symmetry with complicated domain at room temperature, which upon heating changes to a tetragonal phase at about 286°C and then to a cubic phase at TC=394 °C. Crystals of composition x=0.46 exhibit the best piezoelectric properties, with a piezoelectric constant d33=1223 pC/N and an electromechanical coupling factor k33=80%. The (100) plate of the tetragonal crystal with composition x=0.62 is optically isotropic, but the (011) plate shows a small birefringence at 45° (angle between polarizer and <100> direction). This is because of the formation of nano-sized tetragonal domains due to the instability of the ferroelectric phase. A total compensation is achieved in the (100) plate, but in the (011) plate the compensation is only partial. By applying an electric field, macroscopic domains can be induced in a (100) plate at a field of 25kV/cm and the crystal becomes aniso-tropic. Birefringence becomes larger with increasing field and shows a maximum value Δn=0.012 at the field of 30kV/cm. After the electric field is removed, the crystal changes back to isotropic, indicating the field induced macroscopic domain is metastable. We discuss the mechanisms for the formation of domain structures and phase transitions in PZT single crystals and compared them with the behaviour and mechanisms of relaxor ferroelectrics.

V.13.1
14:30
Authors : N. Zhang1,6, H. Yokota2, A. M. Glazer3,5, Z. Ren1, D. A. Keen4, D. S. Keeble5, P. A. Thomas5 and Z.-G. Ye1,6
Affiliations : 1 Department of Chemistry and 4D Labs, Simon Fraser University, 8888 University Drive, Burnaby, BC, V5A 1S6, Canada, 2Department of Physics, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba City, 263-8522, Japan, 3Physics Department, University of Oxford, Parks Road, Oxford, OX1 3PU, United Kingdom, 4ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX, United Kingdom, 5Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, United Kingdom, 6Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education & International Centre for Dielectric Research, Jiaotong University, Xi’an, 710049, China.

Resume : PbZr1-xTixO3 (PZT) is one of the most important and widely used piezoelectric materials. The study of its local and average structures is of fundamental importance in understanding the origin of its high-performance piezoelectricity. Pair Distribution Function analysis and Rietveld refinement have been carried out to study both the short- and long-range order in the Zr-rich rhombohedral region of the PZT phase diagram. The nature of the monoclinic phase across the Zr-rich and morphotropic phase boundary area of PZT is clarified. Evidence is found that long-range rhombohedral and both long- and short-range monoclinic regions all coexist at all compositions. In addition, evidence for a boundary between the R and M regions has finally been found and is shown to be characterized by a change from one type of monoclinic (MA) to another monoclinic (MB) structure.

V.13.2
14:45
Authors : E. Buixaderas, T. Ostapchuk, I. Gregora, J. Hlinka
Affiliations : Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Prague 8, Czech Republic

Resume : The main lattice instabilities of PbZrO3 arise from Pb and O atoms shifts, which induce, in the antiferroelectric phase, a modulation in the ab plane and oxygen tilts. We studied the polarized IR and Raman spectra of oriented single domain plates and the temperature dependence of phonons. We identified separately all symmetry modes and found soft modes of seven different symmetries in the antiferroelectric phase. This can be understood in the frame of a three dimensional lattice model with trilinear coupling terms allowed by symmetry, which can stabilize the antiferroelectric displacements of Pb, within a matrix with tendency to the long range ferroelectric order. [1] The substitution of a small percent of Zr by Ti in this system (1% of Ti) induces very interesting phenomena. We also studied PbZr0.99Ti0.01O3 single crystals by means of micro-Raman scattering and Second harmonic generation. The crystals undergo two first order phase transitions within the approximate temperature range 488?503 K. The presence of the second harmonic signal within the phase transitions, together with the analysis of the Raman spectra, leaded us to the conclusion that the intermediate phase is ferroelectric and, probably rhombohedral with the space group R3m. This result support the model sketched in [1] for the development of the antiferroelectricity in PbZrO3. Support by the Czech Science Foundation is acknowledged (Project 13-15110S). [1] J. Hlinka et al., Phys. Rev. Lett 112, 197601 (2014)

V.13.3
16:15
Authors : E.D. Politova, G.M. Kaleva, N.V. Golubko, A.V. Mosunov, S. Yu. Stefanovich, A.H. Segalla*
Affiliations : L.Ya.Karpov Institute of Physical Chemistry, Obukha s.-st., 3-1/12, b.6, 105064, Moscow, Russia *ELPA Company, Panfilovsky pr. 10, Zelenograd, 124460, Moscow, Russia

Resume : The development of piezoelectric materials with working temperatures > 700 K comprises actual task due to demands of industries and ecological problems. Ceramic solid solutions with based on oxides with perovskite structure (Bi,Pb)(Sc,Ti)O3 and (K0.5,Na0.5)O3 attract much attention due to prospects of their applications at high temperatures. In this work, influence of preparation conditions and various overstoichiometric additives (oxides, chlorides and fluorides in amounts up to 15 w. %) on structure, microstructure, ferroelectric and piezoelectric properties of ceramics (1-x)BiScO3 – xPbTiO3 with x=0.635-0.65 (BSPT) and (K0.5,Na0.5)O3 with compositions close to the Morphotropic Phase Boundaries were studied using X-ray Diffraction, Scanning Electron Microscopy, Second Harmonic Generation, and Dielectric Spectroscopy methods. Piezoelectric parameters d33 and kt of the preliminary poled samples were measured. Optimal conditions for dense and textured ceramics preparation were determined, changes in the phase content and unit cell parameters stimulated by additives observed. The 1st order ferroelectric phase transitions were revealed at temperatures near 700 K. High piezoelectric coefficients d33 ~ 500 pC/N and kt ~ 0.65 were reached in modified BSPT ceramics. Enhancement of piezoelectric properties is discussed in relation to the preparation conditions, type and content of dopants. The work was supported by the RFBR grant 12-03-00388.

V.14.2
17:00
Authors : A. Calka and M. Wyszomirska
Affiliations : University of Wollongong, Faculty of Engineering, Wollongong, NSW2522, Australia

Resume : Many functional materials are traditionally synthesized by slow reaction processes that are energy and time consuming. In the present world there is strong demand on development of modern materials and materials processing methods that could offer rapid reaction rates, energy efficiency and be environmentally safe. Perovskite oxide ceramics have found wide applications in energy storage capacitors, electromechanical transducers and piezoelectric, and ferroelectric devices. The conventional method to prepare Perovskite oxide ceramics is ceramic-powder-based processing, i.e., through solid-state reaction at high temperatures. This process has several disadvantages, such as high-temperature reaction, limited degree of chemical homogeneity, and low sintering ability. Therefore, during past years, several chemical-based processing routes, including freeze-drying, spray-pyrolysis, sol– gel, spray-drying, and pyrolysis of complex compounds, have been developed to prepare powders with more homogeneous composition, improved reactivity, and sintering ability at low temperatures. Recently, non-conventional processing methods such as mechanical alloying and mechano-chemical approaches have been used to create reactions between species. However in this method the reaction kinetics is very slow and processing time long. Here we report application of an Electric Discharge Assisted Mechanical Milling (EDAMM)[1] technique to synthesize various Perovskite oxide ceramics. By using EDAMM, high purity single phase multi-element oxides can be formed in as little as 0.1% of the processing time required in conventional solid-state techniques. An even more important feature of EDAMM is that the crystallite size of the synthesized compound is able to be reduced to nanometer size , by careful selection of electrical (voltage, current, total power) and mechanical (vibration frequency and amplitude) experimental parameters. We use EDAMM for (i) synthesis of oxides from elemental powders by oxidation in oxygen plasma and for (ii) synthesis of single phase multi element oxides from pre-mixed oxides as starting materials. This presentation provides an overview of recent development of EDAMM method and it’s application in rapid synthesis of Perovskite ABO3 type oxide ceramics. The EDAMM technique offers an exciting opportunity to rapidly synthesize a range of new and existing materials to be used in a variety of energy storage applications that include rechargeable lithium batteries, hydrogen fuel cells, and super-capacitors. [1] Nature, 419,(2002)147-151

V.14.5

No abstract for this day

No abstract for this day


Symposium organizers
Jorge IniguezInstitut de Ciència de Materials de Barcelona (ICMAB-CSIC)

Campus UAB 08193 Bellaterra Spain

+34 931 888 786
+34 935 805 729
jiniguez@icmab.es
Krystian ROLEDERInstitute of Physics | University of Silesia

Uniwersytecka 4 40-007 Katowice Poland

+48 32 359 1478
Krystian.Roleder@us.edu.pl
Marina TyuninaUniversity of Oulu

Microelectronics and Materials Physics Labs P.O. Box 4500 FI-90014 Oulun yliopisto Finland

+358 08 5532729
+358 08 553 2728
marinat@ee.oulu.fi