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Lead zirconate PbZrO3 has been the subject of research interest for several dozen years. Recently, even its antiferroelectric properties have started to be questioned, and many researchers still deal with the so-called intermediate phase below Curie temperature (TC), whose existence is not fully understood. It turns out that PbZrO3 doped with Nb exhibits below TC phases with complex domain structures. One of them undergoes self-organization taking place at a constant temperature, and transforms, after several minutes, into a lower phase. This isothermal transition was investigated through dielectric, pyroelectric current and Raman scattering measurements. Discontinuities accompanied it in the permittivity and pyroelectric current. The obtained Raman spectra proved that those discontinuities are strictly linked with the isothermal transition between two intermediate phases. The ordering process in lead sublattice stimulated by thermal fluctuations is discussed as a driving force for this peculiar phenomenon.

During the last decade the cubic perovskite oxide EuTiO3 (ETO) has attracted enormous novel research activities due to possible multiferroicity, hidden magnetism far above its Néel temperature at TN = 5.5 K, structural instability at TS = 282 K, possible application as magneto-electric optic device, and strong spin–lattice coupling. Here we address a novel highlight of this compound by showing that well below TS a further structural phase transition occurs below 210 K without the application of an external magnetic field, and by questioning the assumed tetragonal symmetry of the structure below TS where tiny deviations from true tetragonality are observed by birefringence and XRD measurements. It is suggested that the competition in the second nearest neighbor spin–spin interaction modulated by the lattice dynamics is at the origin of these new observations.

The effects of rhodium (Rh) doping on the elastic properties and phase transition behaviors of reduced BaTiO3 single crystals were investigated in the paraelectric phase by using Brillouin spectroscopy. The Rh doping induced changes in the elastic stiffness coefficients and the elastic anisotropy parameter. The degree of softening of (C11 − C12)/2 became more substantial with Rh doping, indicating that the polarization fluctuations were enhanced by heterovalent Rh3+ doping. This was supported by the much larger temperature range over which the nonzero birefringence was observed. Free charge carriers introduced by Rh doping and oxygen vacancies in the reduced BaTiO3 and their interactions with the lattice seem to be the origin of these anomalous changes in the elastic properties.

Elastic anisotropy and slowness curves of barium titanate (BaTiO3) single crystal in the paraelectric phase were investigated by using Brillouin spectroscopy. The directional dependence of sound velocities of the longitudinal and the transverse acoustic waves in the (001) plane showed a four-fold symmetry typical in the cubic phase. Especially, one of the two transverse modes exhibited a substantial softening along the directions. The sound velocity of this mode decreased significantly as temperature decreased toward the transition temperature, which corresponded to the elastic stiffness coefficient (C11 – C12)/2. This result suggests the tetragonal instability caused by the precursor polar clusters in the paraelectric phase of BaTiO3.

For the first time, a weak ferromagnetic hysteresis loop at room temperature has been observed in PbZr1−xTixO3 (PZT) single crystals. The occurrence of these properties has been related to the presence of oxygen vacancies and/or lower oxidation state of titanium. This proves that ferroelectric and ferromagnetic properties can occur simultaneously in this “famous” piezoelectric perovskite without any magnetic dopant.

Doped SrTiO3 becomes a metal at extremely low doping concentrations n and is even superconducting at n &lt, 1020 cm&minus, 3, with the superconducting transition temperature adopting a dome-like shape with increasing carrier concentration. In this paper it is shown within the polarizability model and from first principles calculations that up to a well-defined carrier concentration nc transverse optic mode softening takes place together with polar nano-domain formation, which provides evidence of inhomogeneity and a two-component type behavior with metallicity coexisting with polarity. Beyond this region, a conventional metal is formed where superconductivity as well as mode softening is absent. For n &le, nc the effective electron-phonon coupling follows the superconducting transition temperature. Effusion measurements, as well as macroscopic and nanoscopic conductivity measurements, indicate that the distribution of oxygen vacancies is local and inhomogeneous, from which it is concluded that metallicity stems from filaments which are embedded in a polar matrix as long as n &le, nc.

Antiferroelectric‐based dielectric capacitors are receiving tremendous attention for their outstanding energy‐storage performance and extraordinary flexibility in collecting pulsed powers. Nevertheless, the in situ atomic‐scale structural‐evolution pathway, inherently coupling to the energy storage process, has not been elucidated for the ultimate mechanistic understanding so far. Here, time‐ and atomic‐resolution structural phase evolution in antiferroelectric PbZrO3 during storage of energy from the electron‐beam illumination is reported. By employing state‐of‐the‐art negative‐spherical‐aberration imaging technique, the quantitative transmission electron microscopy study presented herein clarifies that the hierarchical evolution of polar oxygen octahedra associated with the unit‐cell volume change and polarization rotation accounts for the stepwise antiferroelectric‐to‐ferroelectric phase transition. In particular, an unconventional ferroelectric category—the ferrodistortive phase characteristic of a unique cycloidal polarization order—is established during the dynamic structure investigation. Through clarifying the atomic‐scale phase transformation pathway, findings of this work unveil a new territory to explore novel ferrodistortive phases in energy‐storage materials with the nonpolar‐to‐polar phase transitions.

We have investigated in detail the lattice dynamics of five different perovskite titanates ATiO3 (A = Ca, Sr, Ba, Pb, Eu) where the A sites are occupied by +2 ions. In spite of the largely ionic character of these ions, the properties of these compounds differ substantially. They range from order/disorder like, to displacive ferroelectric, quantum paraelectric, and antiferromagnetic. All compounds crystallize in the cubic structure at high temperature and undergo structural phase transitions to tetragonal symmetry, partly followed by further transitions to lower symmetries. Since the TiO6 moiety is the essential electronic and structural unit, the question arises, what makes the significant difference between them. It is shown that the lattice dynamics of these compounds are very different, and that mode-mode coupling effects give rise to many distinct properties. In addition, the oxygen ion nonlinear polarizability plays a key role since it dominates the anharmonicity of these perovskites and determines the structural instability.

Influence of heterovalent Nb5+ doping of antiferroelectric PbZrO3 single crystal has been investigated. This kind of doping, producing defects in the perovskite matrix, influences the lattice instabilities responsible for phase transition at TC, and for inducing pre- and post-transitional effects. The dielectric, electromechanical, and optical properties were investigated. Opposite to their ceramic analogues, the investigated single crystals show a new phase transition and enlarged temperature ranges of lattice instabilities.

The symmetry of the intermediate high-temperature phase of PbHfO3 has been determined unambiguously to be orthorhombic using a combination of high-resolution X-ray diffraction and birefringence imaging microscopy measurements of crystal plates. While lattice parameter measurements as a function of temperature in the intermediate phase are consistent with either orthorhombic or tetragonal symmetry, domain orientations observed in birefringence imaging microscopy measurements utilizing the Metripol system are only consistent with orthorhombic symmetry with the unit cell in the rhombic orientation of the pseudocubic unit cell.

The temperature dependence of the elastic properties of antiferroelectric PbHfO3 was investigated by Brillouin scattering. The two structural phase transitions of antiferroelectric-antiferroelectric-paraelectric phases were clearly identified by discontinuous changes in the acoustic mode frequencies and the hypersonic damping. The substantial softening of the mode frequency along with the remarkable increase in the acoustic damping observed in the paraelectric phase indicated the formation of precursor noncentrosymmetric (polar) clusters and their coupling to the acoustic waves. This was corroborated by the observation of quasi-elastic central peaks, the intensity of which grew upon cooling toward the Curie point. The obtained relaxation time exhibited a slowing-down behavior, suggesting that the dynamics of precursor clusters becomes more sluggish on approaching the phase transition temperature., Comment: 16 pages, 5 figures

The temperature dependence of all independent elastic stiffness coefficients of cubic BaTiO3 was determined over a wide temperature range from 400 °C to the Curie point (Tc ∼ 131 °C) by using Brillouin light scattering spectroscopy. Among the two elastic eigen-modes corresponding to the two measured transverse acoustic waves, (C11-C12)/2 showed a large softening in the paraelectric phase, while the change in C44 was very small. This result caused the elastic anisotropy A, defined as 2C44/(C11-C12), to increase from ∼2.1 to ∼2.7 upon cooling toward the phase transition temperature. The large elastic anisotropy was attributed to the tetragonal instability and the associated anisotropic polarization fluctuations of precursor polar clusters formed by the correlated Ti motions. The elastic anisotropy was fitted by using the Curie-Weiss law resulting in a significant deviation in a certain temperature range between Tc and ∼Tc + 50 °C, similar to the dielectric permittivity.

The structural instability of SrTiO3 at T S = 105 K is reinvestigated experimentally and theoretically by birefringence measurements and within the self-consistent phonon approximation. Analogous to BaTiO3 the phase transition shows precursor dynamics starting approximately 60 K above the phase transition temperature. These rotational dynamic clusters compete with precursor effects stemming from the polar soft mode and appear on different length scales as compared to BaTiO3.

The influence of a small amount of niobium ions (0.6 mol% $\mathrm{N}{\mathrm{b}}_{2}{\mathrm{O}}_{5}$) introduced into $\mathrm{PbZr}{\mathrm{O}}_{3}$ single crystals on the structural, dielectric, optical, and electromechanical properties was studied. The main goal was to search for the influence of this doping on the phase transition sequence. It was found that addition of Nb leads to stabilization of the known intermediate phase and to formation of a new one. It is interesting that locally broken symmetry could be observed both below and far above the Curie temperature. All these results are analyzed in terms of charge compensation phenomena.

The dynamics of precursor polar clusters in rhodium(Rh)-doped barium titanate single crystals were examined in the paraelectric phase by Brillouin light scattering and birefringence measurements in a wide temperature range. The longitudinal acoustic (LA) mode and central peaks in the inelastic light scattering spectrum were investigated by Brillouin scattering, while the temperature dependence of the birefringence was accurately determined by means of a birefringence imaging system. In a specific temperature range above the ferroelectric phase transition temperature, the LA mode frequency exhibited a significant softening concomitant with the substantial increase in the hypersonic damping, which was attributed to the formation of polar clusters and their interactions with acoustic waves. In this temperature range where acoustic anomalies were brought about, the birefringence showed non-zero values, indicating the existence of local non-centrosymmetric regions. All these results clearly indicated that the ...

The temperature variations of the elastic constant C 11 and the corresponding acoustic attenuation coefficient of barium titanate single crystals grown by two different methods in the paraelectric phase were obtained in a wide temperature by means of Brillouin light scattering. Two phenomenological approaches were adopted to attempt to explain the anomalous change in C 11 (denoted as Δ C 11 ) in the paraelectric phase. Δ C 11 exhibited a logarithmic variation as log[( T − T 0 )/ T 0 ] in a certain temperature range from T c to about T c + 80 °C instead of the other variation of ( T − T 0 ) ζ predicted by the mean-field approach. This temperature range was almost the same as the range where precursor dynamics were theoretically predicted to set in. The fact that the logarithmic variation was proposed for uniaxial systems might indicate that the correlated deformation of precursor polar clusters is tetragonal, as was suggested from nuclear magnetic resonance study [7] .

The temperature dependences of electrostrictive strain and birefringence for a PbZr0.80Sn0.20O3 single crystal have been measured with a high accuracy close to the high temperature phase transitions into the paraelectric phase. Characteristic features are the existence of local maxima on M 11(T) dependence and irregular Δn(T) dependences that indicate existence of an intermediate phase between the antiferroelectric and paraelectric phase. Above TC a local Δn(T) maximum appears on heating caused probably by interactions of polar regions embedded in the non-polar cubic matrix. The existence of these regions could be accounted for by a disorder of Sn ions in the lead zirconate lattice.

Although numerous papers on physical properties of the BaTiO 3 crystal can be found in literature, there is a lack of tentative studies of its properties in temperature range close to but above T C . That is why investigations of temperature dependence of the dielectric properties, electrostrictive strain and thermal expansion have been undertaken. Results obtained point to non-linear behaviour of all these properties even tens degrees above T C . Especially the non-linear thermal expansion, first time measured in detail for BaTiO 3 above T C , implies the existence of micro/nano-polar regions whose temperature stability and sizes are responsible for temperature hysteresis above T C .

PbHfO(3) is investigated theoretically and experimentally with respect to possible precursor effects starting in the paraelectric phase far above the cubic to tetragonal phase transition temperature. The theoretical modeling within the polarizability model predicts a giant softness of the system with spatially large polar and antiferrodistortive domain formation which compete with each other. These predictions are substantiated by the experiments, where the softness and the precursor effects are confirmed by birefringence, dielectric permittivity measurements and elastic properties by Brillouin scattering. The intermediate phase is found to have the polar nature confirmed by P-E hysteresis loop measurements, which is another manifestation of the competition between interrelated instabilities, namely a polar one and an antiferroelectric one.

Order-disorder mechanism is a part of phase transition nature in the ABO3 perovskites. It is related with the existence of polar regions, which dynamics in the electric field determines the dielectric response near T c. Temperature dependence of mechanical strain connected with polarisation change in the paraelectric phase has been investigated for the BaTiO3 and PbZrO3 single crystals. Existence of polar regions influences the electrostrictive properties and induces the piezoelectric effect in the paraelectric phase. A non-linear temperature dependence of the electrostrictive coupling between the macroscopic strain and macroscopic polarisation has been found above T c.

A ceramic of nominal formula Pb0.95Sr0.05(Zr0.53Ti0.47)0.98Nb0.02O3 has been investigated. Dielectric properties and differential scanning calorimetry tests pointed to a transformation temperature of 306??C. By means of a dynamic method the piezoelectric and complex elastic compliances for polarized ceramics have been measured as a function of temperature. The temperature dependence of the elastic properties has indicated bilinear coupling between the order parameter and strain. The unexpected existence of a pertinent piezoelectric response far above accompanied by strong changes in the elastic properties was observed. On the basis of the dielectric response and x-ray diffraction studies carried out on poled and unpoled ceramics, the influence of the compositional fluctuations and the existence of polar regions on the anomalous piezoelectric activity above were considered rather than a change of symmetry after the action of an external electric field.

Infrared reflectivity, time-domain terahertz transmission, high-frequency dielectric measurements and Raman spectroscopy of Na0.5Bi0.5TiO3 complex ferroelectric perovskite were performed in a broad temperature range. The results were analysed considering the macroscopic symmetry as well as symmetry resulting from local Na–Bi ordering in all three known phases. An overdamped infrared soft mode was revealed in the THz range which, together with central-mode type dispersion in the GHz range, contribute to the strong and broad dielectric permittivity maximum around 600 K. Anharmonic Bi and/or Na vibrations and local hopping, respectively, are suggested to be the main origins of these excitations. The broad phonon spectra and the frequency independent dielectric losses at low temperatures are compatible with the existence of nanoscopic polar regions and disorder to liquid He temperatures similar to relaxor ferroelectrics.

The lattice dynamics of Pb-containing perovskite oxides are investigated theoretically for the transition metal series Ti, Zr, Hf, in order to elucidate their commonalities and their distinctions. For all three compounds, pronounced precursor effects are found to their phase transition temperatures, which get more pronounced the heavier the central transition metal ion is. In addition, a competition between a polar and an antiferrodistortive instability is predicted to take place, which is strongly mass dependent. While in PbTiO3 the polar instability wins, both instabilities are active in PbZrO3, whereas in PbHfO3 the antiferrodistortive phase transition dominates the dynamics. For all three compounds, marked anomalies in the elastic constants are predicted, which are most pronounced in PbHfO3. Experimental results for elastic anomalies preceding the phase transition, which agree qualitatively with the model calculations are presented for PbHfO3.

For PbZrO3 and PbZr0.99Ti0.01O3 single crystals the first order Raman light scattering spectra in the paraelectric phase have been analysed. In lead zirconate two kinds of crystals, with and without a transient phase, were investigated. It was found that temperature dependence of the defect-induced soft mode frequency in the paraelectric phase has a negligible contribution to the low-frequency dielectric response. From the point of view of strong dielectric relaxation in the range of 106–109 Hz, which originates in a disorder of the lead sites, crossover of the order-disorder and displacive type of antiferroelectric phase transition in lead zirconate is considered: the phase transition mechanism is neither purely displacive nor order-disorder. Contribution of physical phenomena responsible for the e(ω,T) dielectric response at low frequencies of an external electric field are described.

Dielectric studies of a PbHfO3 (lead hafnate) single crystal undergoing two structural phase transformations at about 163°C (436 K) and 209°C (482 K) were performed in broad frequency and temperature range. Special attention was paid to the paraelectric phase. Investigations of the complex dielectric permittivity in the frequency range 10 Hz to 10 MHz revealed two relaxations of polydispersive and nearly monodispersive (Debye-like) character connected with space charge behaviour. In the frequency range of 106-109Hz a polar relaxation mode has been found and related to a disorder in the Pb sublattice. Temperature dependence of the dielectric step of this relaxation corresponds to a sharp anomaly of the e(T) function at the phase transition from the paraelectric to antiferroelectric state. Analysis of temperature evolution of the first order Raman light scattering spectra showed existence of a soft line at this transformation. Crossover of the displacive and order-disorder type of the transformatio...

Infrared reflection and transmission measurements on PbZrO3 single crystal, ceramic and thin films in the 10-600 K temperature range enabled us to determine the dielectric response function and discuss the dynamic origin of the antiferroelectric transition. The strong dielectric anomaly is caused by an overdamped mode in the 10 cm−1 range which is assigned to anharmonic hopping of Pb atoms whereas the phonon modes contribute only by ∼100 to the relative permittivity value. Thin films show somewhat weaker and more smeared phonon spectra and lower permittivity values.

Transmission electron microscopy and neutron diffraction have been used to characterize ceramics and single crystals from the rhombohedral region of the (x = 0.06-0.45) phase diagram. Electron diffraction patterns showed the existence of superlattice reflections of the type , where h = k = l, and , which are not observed by neutron powder diffraction. The analysis of these reflections also revealed satellite spots around the , which are associated with periodic antiphase boundaries. The origin of these superlattice reflections is explained by the existence of local regions presenting antiparallel cation displacements, and models for this are suggested

Studies of dielectric relaxation have been carried out for a PbHf0.98Ti0.02O3 single crystal in the frequency range 10 Hz-10 MHz in the paraelectric phase. Two dispersive steps of polydispersive and nearly monodispersive (Debye-like) character have been ascribed respectively to space charge and disorder in Pb sublattice recently found by X-ray examination.

Investigations of local electromechanical properties for PbZr1− x Sn x O3 single crystals are a way to understand better the phase transition mechanisms in oxide perovskites with antiferroelectric phase transition. The investigations of local electromechanical studies were performed by the PEFM. The piezoelectric activity in nano-scale and weak birefringence observed in micro-scale have been found in the paraelectric phase and are a proof for theoretically predicted local instability above T C [A. Bussmann-Holder et al., Phys. Rev. B 79, 184111 (2009)]. Origin of these instabilities is analysed taking into account non-homogeneous distribution of Sn in crystal lattice, presence of extended defects and other lattice inhomogeneities. Temperature dependences and thermal hysteresis of piezo- and electrostrictive responses were compared with bulk properties.

The complex perovskite , exhibiting a long-range B-site cation ordering, has been investigated by Raman scattering from 10 K up to 956 K. The Raman results are systematically treated, and analysed through the characteristic parameters of phonon peaks. The existence of an additional intermediate phase I between the low-temperature antiferroelectric phase A and the high-temperature paraelectric phase P has been demonstrated (, ). These results were compared with dielectric measurements. The disappearance of the first-order Raman structures near 1000 K in the paraelectric phase is discussed in terms of dynamic disorder in the Pb and O sublattices.

Three relaxation processes for frequencies from 10 Hz to 10 MHz and for various Ti concentrations in PbZr1-xTixO3 (x

Raman scattering investigations were performed over a large temperature range from 10 to 700 K on pure and Ti-doped PbHfO3 single crystals. The modifications of the Raman spectra were precisely observed in the vicinity of two structural phase transitions occurring in the crystal: an antiferroelectric (A1) to antiferroelectric (A2) phase transition at 436 K and antiferroelectric (A2) to paraelectric (P) phase transition at 484 K. The characteristic parameters of the Raman structures were determined throughout the whole phase transition sequence. The softening of the two lowest-frequency Raman lines seems to have a dominating influence on the slight increase in dielectric permittivity at the A1 to A2 phase transition in both pure and doped samples suggesting a displacive nature for this transition. For Ti-doped samples the form of the A1 to A2 transition is smoother than for undoped samples while the A1 to P transition appears to be unaffected by doping with Ti.

Raman scattering measurements were carried out for the ordered and disordered states of PbIn1/2Nb1/2O3 (PIN) single crystals in the temperature range from 10 K to 1050 K. Sensitivity of the Raman method to the degree of order in the B site cations was confirmed. Sharp changes in the Raman spectra near the phase transition from the antiferroelectric to the paraelectric state (440 K) were detected for the ordered sample. Diffuse changes in the vicinity of the ferroelectric-paraelectric transition were seen in the disordered one. In the paraelectric phase, Raman lines of first order character have been found in the low-frequency range. The disappearance of these lines at higher temperature (1000 K) is discussed from the standpoint of a supplementary structural phase transition.

Investigations of the electric permittivity, elastic compliance, pyroelectric and piezoelectric properties as functions of time and temperature were performed for a PbZr0.985Ti0.015O3 single crystal and compared with Raman scattering data. The e(T) function in the paraelectric and intermediate phase can be described by the stretched exponential functions typical for glass system. Poling of the sample in d.c. electric field induces stable ferroelectric properties in the intermediate phase. In this case the transition to the pure antiferroelectric phase takes place via a transient glass phase.

The elastic properties of KF-substituted perovskite lead titanate ( PbTiO 3) were investigated by dielectric measurements and Brillouin light scattering. The ferroelectric phase transition occurred at substantially lower temperature due to KF substitution, which was attributed to the modification of the covalency in Pb – O and Ti – O bonds. The longitudinal acoustic (LA) mode of KF-substituted PbTiO 3 showed a frequency softening in the paraelectric phase, which was accompanied by increasing acoustic damping. This indicated that polarization fluctuations responsible for the acoustic anomalies were enhanced by KF substitution.

The dielectric, elastic, and piezoelectric properties of a niobium-doped $\mathrm{Pb}{\mathrm{Zr}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{x}{\mathrm{O}}_{3}$ ceramic with a composition located near the morphotropic phase boundary have been studied from $25\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}400\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. A strong softening of the elastic coefficients was observed far below the temperature corresponding to the dielectric permittivity maximum, ${T}_{\ensuremath{\epsilon}\mathrm{max}}=366\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. The steep decrease of the stiffness coefficient ${c}_{44}$ from $400\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}350\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ is probably a stepwise anomaly which is expected at an improper ferroelastic transition. In addition, it was found that all macroscopic piezoelectric activity had disappeared well above ${T}_{\ensuremath{\epsilon}\mathrm{max}}$. This is explained by the combined effects of compositional fluctuations in the $\mathrm{Zr}∕\mathrm{Ti}$ sublattice and the presence of polar nanoregions. The elastic properties have an anomaly at the temperature at which the lattice becomes predominantly centrosymmetric. The piezoelectric activity vanishes when the polar nanoregions reach a critical size below which they can no longer interact coherently through the nonpolar matrix to induce a macroscopic piezoelectric response.

To better understand the phase transition mechanism of PbZrO3 (PZO), the lattice dynamics of this antiferroelectric compound are investigated within the polarizability model, with emphasis on the cubic to orthorhombic phase transition. Similarly to ferroelectric phase transitions in ABO3 perovskites, polar dynamical clusters develop and grow in size upon approaching T(C) from the high temperature side and never form a homogeneous state. Simultaneously, elastic anomalies set in and compete with polar cluster dynamics. These unusual dynamics are responsible for precursor effects that drive the PZO lattice towards an incipient ferroelectric state. Comparison of the model calculations with the temperature dependences of elastic coefficients measured on PZO single crystals reveals a striking similarity.

Light-scattering investigations in the temperature range from 10 to 850K have been performed on single crystals of silver niobate AgNbO3. The results are compared with structural and dielectric measurements revealing a complex sequence of phases. The Raman results and especially the strong central peak, which occurs over a wide range of frequencies and temperatures, are analysed in connection with the various phase transformations. The specific contributions of the niobium and the silver ions are tentatively discussed.

Detailed investigations of the pyroelectric and dielectric properties were performed on PbZrO3 single crystals grown from PbO + ZrO2 + PbF2 + B2O3 flux. Virgin samples possessed a spontaneously developing transient phase. The influence of space charge polarization, in particular connected with the special role of vacancies in Pb and O sublattices, on the temperature changes of proper pyroelectric current inside the ferroelectric phase is considered. Also the residual current observed above the Curie temperature and below the transition temperature to the antiferroelectric phase is discussed in detail.

The temperature dependence of Raman scattering near the phase transition points between antiferroelectric orthorhombic(Aa), ferroelectric rhombohedral (FR) and paraelectric cubic (PC) phases was investigated in PbZrO3 crystals. The measurements were carried out with simultaneous observations of the electric permittivity along the [111] direction. The ferroelectric nature of the intermediate phase had previously been observed by the hysteresis loop and pyroelectric tests. The evolution of the Raman spectra from Aa to Pc through the FR phase is reported. The main modification of the Raman spectrum takes place at the temperature at which e(T) begins to exhibit significant variations.

Piezoelectric properties of Na0.5Bi0.5TiO3 ceramics have been investigated over a broad temperature range using a resonance technique. The thermal behaviours of the piezoelectric tensor coefficients d31, d33 and d15 confirm that there is a distinct phase transformation at 200 °C. For the first time it has been found that a piezoelectric signal connected with the tensor component d33 is observed up to 280 °C. This corresponds to earlier neutron and x-ray diffraction data on the point of transition from rhombohedral to tetragonal symmetry.

We report the results of comprehensive study of the critical dynamics of the prototype perovskite antiferroelectric PbZrO$_3$. The combination of inelastic X-ray and diffuse X-ray scattering techniques and Brillouin light scattering was used. It is found that the dispersion of the TA phonons is strongly anisotropic. The dispersion curve of the in-plane polarized TA phonons propagating in [1 1 0] direction demonstrates pronounced softening. Slowing down of the excitations at R-point is found, it is manifested in growing of the central peak. This slowing down is too weak to be considered as a primary origin of the corresponding order parameter. Obtained results are treated in terms of TA--TO flexoelectric mode coupling. It is demonstrated that the structural phase transformation in PbZrO$_3$ can be considered as the result of the only intrinsic instability associated with the ferroelectric soft mode., 13 pages, 8 figures

Silver niobate AgNbO3 is a perovskite compound which undergoes a complex series of structural phase transitions. Raman scattering experiments have been performed on single crystals between 300 and 650 K. The analysis of the data, in using a suitable lineshape Raman function, reveal the presence of a broad central component in addition to an underdamped soft phonon line. A very diffuse phase transition is found to be connected to the occurence of the central peak whereas a very sharp transition can be associated to the abrupt soft-phonon disappearance.