Relaxor ferroelectrics

A novel methodology is presented for identifying and distinguishing between structural phases in multi-phasic systems, such as piezoelectric materials like PMN–PT [Pb(Mg1/3Nb2/3)O3–PbTiO3], PIN–PMN–PT [Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3] and PZT [Pb(Zr,Ti)O3], using diffuse multiple scattering and Kossel line diffraction techniques. The method exploits the splitting of triple line intersections from special coplanar reflections combined with logical constraints to generate a splitting fingerprint for robust crystallographic phase determination and discrimination.

Diffuse neutron scattering is a valuable tool to obtain info rmation about the size and orientation of the polar nanoregions that are a characteris tic feature of relaxor ferroelectrics. In this paper, we present new diffuse scattering results obtained o Pb(Zn1/3Nb2/3)O3 (PZN for short) and (1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 (PZN-xPT) single crystals (withx=4.5 and 9%), around various Bragg reflections and along three symmetry directions in the [100]-[011] zone. Diffuse scattering is observed around reflections with mixed indices, (100), (0 11) and (300), and along transverse and diagonal directions only. No diffuse scattering is found in lo gitudinal scans. The diffuse scattering peaks can be fitted well with a Lorentzian function, from whic h a correlation length is extracted. The correlation length increases with decreasing temperature s down to the transition at Tc, first following a Curie-Weiss law, then departing from it and becoming flat at very low temperatures. These results are...

Neutron inelastic scattering measurements of the polar TO phonon mode in the cubic relaxor Pb(lMg1,sNb2,s)03, at room temperature, reveal anomalous behavior similar to that recently observed in Pb(Znl/sNb2,s)0.92Ti0.0d0s in which the optic branch appears to drop precipitously into the acoustic branch at a finite value of the moment,um transfer q = 0.2 A-', measured from the zone center. By contrast, a recent neutron study indicates that PMN exhibits a normal TO phonon dispersion at 800 K. We speculate this behavior is common to all relaxor materials, and is the result of the presence of nanometer-scale polarized domains in the crystal that form below a temperature Td, which effectively prevent the propagation of long wavelength (q = 0) phonons.

The wave vector and temperature dependences of transverse acoustic modes propagating along the [001] and polarized along the [100] orthorhombic axis in KNbO3 have been studied by means of coherent inelastic neutron scattering methods. The results are consistent with previous elastic constant and neutron scattering measurements. The mechanism of the orthorhombic-tetragonal phase transition is discussed in the light of all these data.

Lix(Sr0.5Ba0.5)1-x/2Nb2O6 ceramics were prepared by a solid state synthesis and sintered at 1300 • C. XRD investigations reveal single phase samples up to a substitution limit of x = 0.275. For higher lithium contents, the appearance of LiNbO3 as secondary phase was observed. The density of the ceramics increases with lithium content. The microstructures show globular grains which turns to pillar-like grains with rising lithium substitution. Dielectric investigations confirm relaxor ferroelectric behavior and the diffuse phase transition is shifted towards higher temperatures with increasing lithium content from 129 • C (x = 0) to 221 • C (x = 0.275). The diffuseness coefficient increases with the lithium content. From high-temperature XRD measurements the length of the tetragonal cell parameter c decreases with increasing temperature, reaches a minimum at about 150-230 • C (depending on x) and afterward increases with increasing temperature. Additionally, a significant shift of the Nb(2) position with temperature can be observed.

Submitted for the MAR06 Meeting of The American Physical Society Composition dependence of the diffuse scattering in relaxor (1x)Pb(Mg 1/3 Nb 2/3 )O 3 -xPbTiO 3 (0 ≤ x ≤ 0.40) M. MATSUURA, K. HIROTA, ISSP The University of Tokyo, P. M. GEHRING, NIST Center for Neutron Research, ZUO-GUANG YE, W. CHEN, Department of Chemistry Simon Fraser University, G. SHIRANE, Deapartment of Physics Brookhaven National Laboratory -We have studied composition dependence of diffuse scattering in the relaxor sys 10, 20, 30, and 40% by neutron diffraction. The addition of ferroelectric PbTiO 3 (PT) modifies the "butterfly" and "ellipsoidal" diffuse scattering patterns observed in pure PMN (x = 0), which are associated with the presence of randomly oriented, polar nanoregions (PNR). The spatial correlation length ξ derived from the width of the diffuse scattering increases from 12.6 Å for PMN (x = 0) to 350 Å for PMN-20%PT, corresponding to an enlargement of the PNR. The integrated diffuse scattering intensity, which is proportional to χ ′′ , grows and reaches a maximum at x = 20%. Beyond x =30% PT, a concentration very close to the morphotropic phase boundary (MPB), no diffuse scattering is observed below T C , and well-defined critical behavior is observed. By contrast, the diffuse scattering for x ≤ 20% persists to low temperatures, where the system retains an average cubic structure (T C = 0). We can simulate the wave vector dependence of the diffuse scattering by assuming that it arises from the condensation of a soft transverse-optic (TO) phonon.

Recently, a new orthorhombic phase has been discovered in the ferroelectric system (1x)Pb(Zn 1/3 Nb 2/3 )O3-xPbTiO3 (PZN-xPT) for x= 9%, and for x= 8% after the application of an electric field. In the present work, synchrotron x-ray measurements have been extended to higher concentrations, 10% ≤ x ≤15%. The orthorhombic phase was observed for x= 10%, but, surprisingly, for x ≥11% only a tetragonal phase was found down to 20 K. The orthorhombic phase thus exists only in a narrow concentration range with near vertical phase boundaries on both sides. This orthorhombic symmetry (MC-type) is in contrast to the monoclinic MA-type symmetry recently identified at low temperatures in the Pb(Zr1-xTix)O3 (PZT) system over a triangle-shaped region of the phase diagram in the range x= 0.46-0.52. To further characterize this relaxor-type system neutron inelastic scattering measurements have also been performed on a crystal of PZN-xPT with x= 15%. The anomalous soft-phonon behaviour ("waterfall" effect) previously observed for x= 0% and 8% is clearly observed for the 15% crystal, which indicates that the presence of polar nanoregions extends to large values of x.

We have performed neutron scattering studies on low energy phonon modes in the multiferroic BiFeO 3 . We show measurements near (100), ( ), (200) Bragg peaks on the TA, LA and lowest energy TO modes in a broad temperature range from 300 K to 700 K. The intensities, dispersion, and life times (inversed energy width) of these phonon modes are plotted vs. temperature, and anomalies related to the AFM order (Neel temperature of 640 K) are discussed. We also will also discuss additional low energy modes observed that may be related to the "electro-magnon" excitations in this material. This work is supported by the Office of Basic Energy Sciences, DOE.

We have performed inelastic neutron scattering studies of the low-energy phonon and spin-wave modes in the multiferroic BiFeO3. The low-energy phonon and spin wave dispersion relations along different directions have been mapped out over a broad temperature range from 100K to 750K. The temperature dependence of the intensities, dispersion relations, and lifetimes (inverse energy width) of these phonon and spin wave modes will be presented. Possible interactions between the lattice and spin dynamics will also be discussed. This work is supported by the Office of Basic Energy Sciences, DOE.

to measure both acoustic and optic phonons polarized along (110) (T2 mode) in the relaxor ferroelectric compound PZN-4.5PT. In the low temperature rhombohedral phase, a single domain state was achieved by cooling the single crystal sample under an external electric field of 2 kV/cm along the [111] direction. Phonon measurements were performed near the (2,2,0) and (2,-2,0) Bragg peaks. We have found that the TA2 phonon couples closely to the diffuse scattering, which arises from polar nano-regions in the system. With the redistribution of diffuse scattering under the external field (see Ref. 1), a clear hardening of TA2 mode was observed near the (2,2,0) Bragg peak, while the TA2 mode near (2,-2,0) Bragg peak softens significantly and becomes over-damped. Our results indicate local inhomogeneities such as the PNR can have direct and significant effects on the lattice dynamics and stability of the whole system. Ref. 1: "Electric-field-induced redistribution of polar nano-regions in a relaxor ferroelectric", Guangyong Xu, Z. Zhong, Y. Bing, Z.-G. Ye, and G. Shirane, Nature Materials 5, 134, (2006).

Molecular dynamics simulations were performed on a first-principles-based effective Hamiltonian for Pb͑Sc 1/2 Nb 1/2 ͒O 3 ͑PSN͒ with nearest neighbor Pb-O divacancy pairs. Simulations were performed for PSN with ideal chemical order, chemical short-range order, and random chemical disorder. Divacancy concentration vs temperature, X ͓Pb-O͔ vs T, phase diagrams were calculated, and they are shown to be topologically equivalent to the previously calculated hydrostatic pressure vs temperature diagram. In PSN with ideal chemical order, the Burns temperature defines an isotherm, which is analogous to the "Griffiths phase" in the magnetic dilution problem.

Strontium barium niobate, (Sr,Ba)xNb₂O₆ (SBN), is known for its remarkable ferroelectric properties, pyroelectric and linear electro-optic coefficients, and strong photorefractive effects. These characteristics make SBN highly desirable for technological applications such as storage media for holograms, pyroelectric and piezoelectric applications, and electro-optic data storage. By carefully controlling the cooling rate during calcination and optimizing the sintering temperature, single-phase pure Sr₀.₇₅Ba₀.₂₅Nb₂O₆ (SBN25) and Sr₀.₅Ba₀.₅Nb₂O₆ (SBN50) ceramics were synthesized using a simple solid-state reaction route. The material calcined at 1250°C and sintered at 1300°C stabilized in a pure phase with a tetragonal structure in the P4bm space group, achieving a density >95%. The lattice parameters were found to be a = 12.467(4) Å, c = 3.956(5) Å for SBN25, and a = 12.435(2) Å, c = 3.945(7) Å for SBN50. Both compositions exhibited relaxor-type behavior with diffuse phase transitions. The dielectric data were analyzed using the Modified Curie-Weiss law, while dielectric relaxation followed the Vogel-Fulcher relationship with freezing temperatures of 277.3K for SBN25 and 278.4K for SBN50. Significant dielectric dispersion was observed in the low-frequency and low-temperature regime in both components of dielectric permittivity, with a small dielectric relaxation peak detected in the temperature range 323-473K, attributed to a defect-related hopping process. Cole-Cole analysis further indicated the polydispersive nature of the dielectric relaxation.

BSZT40NF has been doped with rare earth oxides (Erbium, Holmium and Samarium) in an attempt to understand the effect on the reliability of the dielectric material for multilayer capacitor and tunable microwave applications. The morphology of the samples used was characterized using scanning electron microscopy (SEM) used to confirm the presence of each rare earth ions. It is suggested that incorporation of rare earth ions into the BSZT40NF is as a result of ionic radius, resulting in varying grain growth and tunable properties. The change in reliability and tunable properties of the capacitor and microwave devices can be attributed to overall distribution of rare earth oxides and their occupation site within the BSZT40NF dielectric. Term Index: BSZT40NF, rare earth ions, SEM, Tunable properties.

Ceramics based on lead zirconate-titanate Pb(Zr0.70Ti0.30)O3 (PZT), bismuth manganite (BM) and the composite (1 − x) PZT–x BMwere obtained. A systematic study of linear and nonlinear dielectric susceptibilities temperature and frequency dependences was conducted. A composition-induced crossover in nonlinear dielectric susceptibility was detected. The so-called scaled nonlinear susceptibility, a3, was obtained from experimental values of the real part of the linear and third-order nonlinear dielectric susceptibilities. The value for a3 was negative for low BM content in the whole temperature range specific to discontinuous ferroelectric phase transitions and relaxor behavior. In contradiction, a3 was positive for BM and for the composite with sufficiently high BM content. The positive a3 was attributed to a subsystem of dipoles created by trapped charges. Hopping charge transfer, which is a dominant mechanism for conduction in manganites, is responsible for the positive a3 and for th...

We show that, in relaxors, the transverse acoustic (TA) mode displays a particularly original behavior, due its coupling to the transverse optic (TO) mode as well as to the polarization P of the Polar Nano-Domains (PND) that are ubiquitous in these special ferroelectrics. A neutron scattering study of the TA phonon frequency and damping, and especially of their q dependence, reveals that the PNDs condense in the form of platelets. In the relaxor range of temperatures, in which elastic diffuse scattering is also observed, the TA mode is strongly scattered by the PNDs. We compare our results with those from thermal conductivity studies of inhomogenous solids and similar neutron results obtained in other perovskite systems. We also present a theoretical model that describes the scattering mechanism specific to relaxors, the TA-P-TO interaction, is shown to fit the acoustic data well and also provides an estimate of the TO mode frequency and damping.

Relaxors like PMN and PMN based materials proved to be promising candidate for multilayer capacitors (MLCs) and electrostriction actuators , pyroelectric bolometers, piezoelectric sensors replacing normal ferroelectrics such as BaTiO 3 and PZT. The compositional heterogeneity resulting from scale of ordering at the B-site influences relaxor to normal ferroelectric behavior .The genesis and growth of PMR resulted in ferroelectric transition. The distribution of curie points in PMR leads to DPT behavior. The dielectric relaxation is attributed to the relaxation of domain walls. Strong charge effects developed as a result of 1:1 ordering at the B-site limits the ordering of domains hence the size growth. The difference between NFE and RFE along with mechanism influencing the transition from RFE to NFE have been discussed.

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The pair distribution functions ͑PDF͒ of BaTi 1−x Zr x O 3 ͑BTZ͒ relaxors ͑x = 0.25, 0.32, 0.35͒, as well as those of the end members BaTiO 3 and BaZrO 3 , were determined at 300 K from neutron powder scattering data. In the relaxors, the PDF provides direct evidence that the Ti and Zr atoms do not occupy the equivalent octahedral sites expected from the crystallographic cubic perovskite structure. It is shown that the TiO 6 and ZrO 6 octahedra in BTZ relaxors are instead similar to those observed in BaTiO 3 and BaZrO 3 , respectively. In BaZrO 3 , the Zr atoms lie at the center of regular oxygen octahedra, forming nonpolar ZrO 6 units. In the tetragonal ferroelectric phase of BaTiO 3 , the distribution of Ti-O distances within TiO 6 octahedra is found compatible with a displacement of the Ti atoms in the ͓111͔ p direction of the pseudocubic perovskite cell. We conclude that the local polarization in BTZ relaxors is mainly due to the displacements of the Ti atoms and that moreover the Ti displacements are very similar in BTZ relaxors and in the classical ferroelectric BaTiO 3 .

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In this work, a model based on the existence of polarized nanoregions (PNRs) in a dielectric matrix is presented for a quantitative analysis of the hysteresis behavior in relaxor ferroelectrics. The PNRs are simulated by spheroids covered with a thin dielectric envelope. The electric field dependence of the polarization is described by the Landau-Ginzburg-Devonshire equation. The phase transition temperature of the individual spheroids appears to be strongly dependent on its orientation relatively to the external electric field. In addition, it depends on the aspect ratio of the spheroid and its size. The polarization in a relaxor ferroelectric was calculated by summation of the polarizations of individual spheroids. The final result is obtained by replacing the sum by a convolution integral of averaged angular dependence of polarization and the PNR size distribution. The obtained theoretical calculations are compared with experimental results.

The behavior of the dielectric response in relaxor ferroelectric materials is studied by means of Monte Carlo simulations of a simple two-dimensional (2D) generic model. It is showed that the shifting with the frequency of the peak of the temperature dependence of the dielectric permittivity e can be obtained just by considering a randomly distributed pinning anisotropy for the out-plane projection of the polar nanoregions. It is also showed that the consideration of a weak long-range dipolar interaction between nanodomains continuously drives the system to a non-relaxor ferroelectric state in which a single peak is observed for the dielectric permittivity. ß 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 6 O. García-Zaldívar et al.: Loss of relaxor properties due to dipolar interactions physica s s p status solidi b

Please check the following details for your article Synopsis: A low-to high-temperature neutron diffraction study of some (K x Na 1Àx)NbO 3-based ceramics has been carried out. The structure of these ceramic compositions has been determined using Rietveld refinement.

Relaxor ferroelectric Sr 4 CaLaTi 3 Nb 7 O 30 ceramics were prepared by using the conventional solid state reaction technique. Dielectric property and ferroelectric transition were studied in detail over a broad temperature range. X-ray diffraction analysis revealed that the Sr 4 CaLaTi 3 Nb 7 O 30 ceramics crystallizes in the tetragonal tungsten bronze structure with space group P4bm. The dielectric studies confirmed two relaxation regions due to the formation of the polar nanoregions below the deviation temperature $405 K. Relaxations I and II were attributed possibly due to the relaxational contributions from dipole reversal of polar nanoregions and fluctuation of polar nanoregion boundaries, respectively. A maximum dielectric constant of 1177 was found at a measuring frequency of 500 Hz. Room temperature polarization-electric field (P-E) hysteresis loops were assessed and a remnant polarization of 0.65 μC/cm 2 with a coercive field of 3.33 kV/cm was observed under an applied electric field of 58 kV/cm. The Sr 4 CaLaTi 3 Nb 7 O 30 ceramics exhibited a prominent dielectric and ferroelectric performance which indicates the potential application of this material in various electronic devices.

NOTICE: this is the author’s version of a work that was accepted for publication in Acta Materialia. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Acta Materialia, 2011, v.

Many metallic alloys, intermetallic compounds and metal hydrides show disordered crystal structure (partly or mixed occupied and/or split or close atomic sites) when Bragg scattering is analyzed by the Rietveld method. If the crystal appears from Bragg scattering as disordered, it does not mean that it cannot be ordered locally. Significant, and often sufficient, information about the local order can be gleaned from the analysis of the atomic Pair Distribution Function (PDF) obtained from the Total Scattering which samples Bragg and diffuse scattering data of a polycrystalline sample simultaneously. The local ordering in apparently disordered crystal is of high importance in determining the materials property, and helps to understand the chemical bonding in the crystal. We will show on two examples what is possible to learn from the PDF obtained from a powder sample: The crystal structure of YCu 6.576 , a substitution variant of the CaCu 5-type, was shown to contain Cu 2-dumbbells replacing Y-atoms in a fraction s=0.19 in the formula Y 1-s Cu 5+2s. The structure type TbCu 7 is assigned to the disordered structure. The local order in the vicinity of the Cu 2-dumbbells has been derived from the PDF obtained from the X-ray powder data [1]. The coordinating Cu 6-hexagon around the dumbbell site shows a shrinkage of 0.33(1) Å w.r.t. the equivalent environment of the Y-atom. No adjacent Y-atoms are substituted but a hexagonal arrangement of Cu 2-dumbbells exists in layers perpendicular to c. The stacking along [001] is random and can be modeled locally from the PDF data consistent with both ab-and abc-type stacking. Therefore, the local order is comparable to that in Ni 17 Th 2-and Th 2 Zn 17structure types, ordered variants of TbCu 7. These results agree with the recent atomistic simulations based on interatomic pair potentials extracted from ab-initio calculated total energy curves by adopting modified Möbius inversion method [2]. Deuterium local order in cubic Laves phase deuteride YFe 2 D 4.2 was studied by neutron (ToF) powder diffraction experiments and PDF modeling [3]. The minimal D-D distance in a metal hydride of 2.1 Å (Switendick rule) has been experimentally proved in the HT-disordered phase. The distribution of deuterium atoms around the iron is not random, and cannot be explained only by applying the Switendick rule. The local order of deuterium atoms within the first iron coordination sphere in the HT-disordered phase above 343 K is similar to the iron coordination in the LT-ordered phase. Same composition of the coordination polyhedra FeD 5 and FeD 4 was found in both phases by Reversed Monte Carlo modeling of the PDF. The exact shape of the FeD 5 and FeD 4 coordination polyhedra in the HT-disordered phase cannot be, however, unambiguously revealed by the PDF analysis.

The elastic and inelastic components of y-ray scattering from a non-transforming VaSi single crystal have been measured using a 57CO Mossbauer source and resonant absorber. The system places an upper limit of � 4 x 10 - 8 e V on the possible energy transfer which distinguishes inelastic from elastic scattering. The scattering at the (440) Bragg reflection with q = 0 and q - 0�1 A -1 has been measured as a function of temperature for two orthogonal orientations of the crystal. Anomalous changes in the elastic and inelastic intensities have been observed. It is suggested that these changes are associated respectively with central mode and soft mode aspects of the dynamics of the vanadium atoms.

The local compositional heterogeneity associated with the short‐range ordering of Mg and Nb in PbMg1/3Nb2/3O3 (PMN) is correlated with its characteristic relaxor ferroelectric behavior. Fully ordered PMN is not prepared as a bulk material. This work examines the relaxor behavior in PMN thin films grown at temperatures below 1073 K by artificially reducing the degree of disorder via synthesis of heterostructures with alternate layers of Pb(Mg2/3Nb1/3)O3 and PbNbO3, as suggested by the random‐site model. 100 nm thick, phase‐pure films are grown epitaxially on (111) SrTiO3 substrates using alternate target timed pulsed‐laser deposition of Pb(Mg2/3Nb1/3)O3 and PbNbO3 targets with 20% excess Pb. Selected area electron diffraction confirms the emergence of (1/2, 1/2, 1/2) superlattice spots with randomly distributed ordered domains as large as ≈150 nm. These heterostructures exhibit a dielectric constant of 800, loss tangents of ≈0.03 and 2× remanent polarization of ≈11 µC cm−2 at room te...

Super ionic material KAg 4 I 5 was synthesized by two methods i.e "solution evaporation method" and "firing method". Highly pure AgI and KI were used as raw materials for synthesis. The powder obtained by "solution evaporation method" was dried, ground and then heated at 162 0 C for 14 hours in air, then ground before characterisation studies. In "firing method" mixture was heated and quenched and then ground followed by heating at 162 0 C for 18 hours before final grinding and characterisation studies. Present investigation is undertaken to compare two methods of preparation of super ionic conductor KAg 4 I 5 since very little work has been done on this compound. Lattice constant of the material was obtained from diffraction photographs obtained from Debye-Scherrer camera. Differential thermal analysis(DTA) shows, greater proportion of super ionic compound obtained when synthesized by first method. Though the measured electrical conductivity obtained by first method is higher than that of second method, activation energy of charge transport is found to be the same in both.

A novel high-entropy perovskite powder with the composition Bi0.2K0.2Ba0.2Sr0.2Ca0.2TiO3 was successfully synthesized using a modified Pechini method. The precursor powder underwent characterization through Fourier Transform Infrared Spectroscopy and thermal analysis. The resultant Bi0.2K0.2Ba0.2Sr0.2Ca0.2TiO3 powder, obtained post-calcination at 900 °C, was further examined using a variety of techniques including X-ray diffraction, Raman spectroscopy, X-ray fluorescence, scanning electron microscopy, and transmission electron microscopy. Ceramic samples were fabricated by conventional sintering at various temperatures (900, 950, and 1000 °C). The structure, microstructure, and dielectric properties of these ceramics were subsequently analyzed and discussed. The ceramics exhibited a two-phase composition comprising cubic and tetragonal perovskites. The grain size was observed to increase from 35 to 50 nm, contingent on the sintering temperature. All ceramic samples demonstrated rela...

Dielectric properties of BaTiO 3 (BT), BaTiO 3 +0.1wt.%MnO 2 (BTMn) and BaTiO 3 +0.1 wt.%Fe 2 O 3 (BTFe) solid solution was investigated. The effects of substitution on the microstructure and on the electric properties of BaTiO 3 samples were studied by performing X-ray diffraction and electric measurements. X-ray diffraction analysis of the samples shows the formation of single-phase compound with a tetragonal structure at room temperature. SEM microphotographs exhibit the uniform distribution of grains. The electric properties (a real part of electrical permittivity(ε') and an imaginary part of electric modulus (M")) were investigated in the temperature range from 150K to 600K and in the frequency range from 0.1 Hz to 10 MHz. It was found that a Fe and Mn ions-doping influence the electric properties of the investigated polycrystalline materials.

High sensitivity measurements of the dielectric constant of solid oxygen are reported for 4 Ͻ T Ͻ 54 K. The results show unexpectedly large hysteresis effects for the temperature dependence of the dielectric constant in the ␣ and ␤ phases of oxygen on thermal cycling below 44 K. The behavior is compared to that observed for solid N 2-Ar mixtures where the geometrical frustration of the molecular orientational ordering leads to pronounced memory effects. In contrast to solid N 2-Ar where the effects of frustration and disorder combine to form an orientational glass, there is no disorder present for pure O 2 and the hystereses are attributed to the strong frustration of the interactions.

Single phase and dense BaZr x Ti 1 À x O 3 (BZT) ceramics (x ¼ 0.05, 0.1, 0.15, 0.2, 0.25) were obtained by microwave sintering and the powders of these ceramics were synthesized by conventional hydrothermal method. The microstructural, dielectric and ferroelectric properties of BaZr x Ti 1 À x O 3 ceramics sintered at 1300 o C were investigated. The XRD analysis revealed that the synthesized compound was formed with no second phase. As x was increased from 0.05 to 0.25, the average grain size was observed on the SEM micrographs to decrease from $6 μm to $3 μm. The dielectric constant as a function of temperature showed a decrease in Curie temperature (T C) with an increasing x, while the maximum value of dielectric loss occurred (tan δ) at x ¼0.1. A ferroelectric-relaxor crossover was observed to take place with increasing x by using the modified Curie-Weiss law. The remnant polarization (P r) decreased from 9.45 to 4.4 C/cm 2 with an increasing x, while the maximum value of P r ¼11.84 also occurred at x ¼0.1. The breadth of T C range increased rapidly when x o0.15, but no significant difference was observed with further doping of Zr 4 þ. The full width at half maximum (FWHM) was used to show the degree of the broadening in Curie peak.

Microsymposia of temperature and pressure are presented. As we shall discuss, the experimental findings allow us to relate the intermolecular hydrogen bonding response to the dynamical behavior of the molecular fragments, which justify the ability of the structure to mechanical relaxation.

The characteristics of a new ferroelectric measurement system at the European Synchrotron Radiation Facility are presented. The electric-field-induced phase transitions of Pb(Mg 1/3 Nb 2/3)O 3-xPbTiO 3 are determined via in situ measurements of electric polarization within the synchrotron diffraction beamline. Realtime data collection methods on single-crystal samples are employed as a function of frequency to determine the microstructural origin of piezoelectric effects within these materials, probing the dynamic ferroelectric response.

Thermal conductivity measurements have been carried out on single crystals of SrTiO 3 and KTaO 3 in the presence of electric fields applied either perpendicular or parallel to the heat current. In the case of SrTiO 3 , the response is surprisingly large: a 7 kV/cm parallel field increases the thermal conductivity by up to 400%. A pronounced anisotropy in both materials, which becomes apparent above nearly the same temperature, is also observed. These effects can be interpreted qualitatively using a simple model in which TA phonons in an energy band near the soft TO mode scatter off of either impurities, ferroelectric microregions, or quantum ferroelectric fluctuations.

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Lacunar spinel is a class of compounds that are derivative of the spinel family, AB2X4, with some vacancies at the A-site. They are very interesting both crystallographically and with respect to the physical properties as several members exhibit structural phase transition from F-43m to R3m and long-range magnetic ordering at low-temperature.[1,2] Having R3m (C3v symmetry) space group along with long-range magnetism make these compounds interesting in the aspect of spintronics, as they may host Néel-type skyrmions.[3] One such very well-studied compound is GaV4S8 that hosts skyrmion with individual size of 22 nm. [3] Here, we report a study on a different member of the lacunar spinel family, GaMo4Se8 that is expected to have smaller skyrmions size. We performed high-resolution powder neutron diffraction across the structural phase transition (TS = 51 K). Through Rietveld refinement, it is found out that there are two coexisting low-temperature crystal structures with space group R3m (major phase) and Imm2 (minor phase) (Fig.1), which is very unique only for GaMo4Se8.[4] We propose an explanation for the coexisting of both crystal structures through mode-crystallographic and bond-valence sum analysis and postulate that the large strain in the rhombohedral structure is alleviated by the formation of the orthorhombic phase with larger displacive distortion amplitude. Furthermore, we have carried out magnetization measurements and performed magnetic critical behavior analysis. We find that the magnetic transition in GaMo4Se8 is close to a tricritical mean-field model, and the analysis of the magnetic phase diagram using magneto-entropic map revealed a positive phasefield which might be an indication of the presence of complex magnetic structures such as cycloid or skyrmions states. Figure 1. The percentage change in cubic (F-43m), rhombohedral (R3m), and orthorhombic (Imm2) phases of GaMo4Se8 as a function of temperature. The Mo4 tetrahedron (green color) corresponding to each phase is shown along with the possible distortion direction (red color arrow).

Barium titanate ceramics have been obtained by sol-gel methods. The dielectric investigations of these materials revealed the existence of diffuse ferroelectric transitions. By using a phenomenological model, we could demonstrate the existence of a simple relationship between the diffuse character of the transition and the sample grain-size. This effect has been attributed to interactions between charged defects on the grain surfaces and the spontaneous polarization of the material.

Inelastic x-ray and neutron scattering were used to measure two matching lattice excitations on the ͓01͔ zone boundary in ␣-uranium. The excitations have the same polarization and reciprocal-space structure, but one has energy consistent with the thermal activation energy of the other, indicating that it creates the mode. The implied mechanism, where a mode is created by an amplitude fluctuation that mirrors the mode itself, is consistent with an intrinsically localized mode ͑ILM͒, and this is supported by thermodynamic data. The reciprocal-space structure, however, indicates a mode that is extended along its polarization direction, ͓010͔, and yet fully localized along a perpendicular direction, ͓001͔. An enhancement of the thermal but not electrical conductivity with mode activation also suggests that these modes are more mobile than conventional ILMs. The behavior is, however, qualitatively similar to that predicted for ILMs on two-dimensional hexagonal lattices, where in-plane localization has been shown to be extended over more than ten discrete units, and the modes can be highly mobile.

In previous work, molecular dynamics simulations based on a first-principles-derived effective Hamiltonian for Pb 1-X (Sc 1/2 Nb 1/2)O 3-X (PSN), with nearest-neighbor Pb-O divacancy pairs, was used to calculate X [Pb-O] vs. T, phase diagrams for PSN with: ideal rock-salt type chemical order; nanoscale chemical short-range order; and random chemical disorder. Here, we show that the phase diagrams should include additional regions in which a glassy relaxor-phase (or state) is predicted. With respect to phase diagram topology, these results strongly support the analogy between relaxors and magnetic spinglass-systems.