An entry from the Inorganic Crystal Structure Database, the world’s repository for inorganic crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the joint CCDC and FIZ Karlsruhe Access Structures service and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Inorganic Crystal Structure Database, the world’s repository for inorganic crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the joint CCDC and FIZ Karlsruhe Access Structures service and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Inorganic Crystal Structure Database, the world’s repository for inorganic crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the joint CCDC and FIZ Karlsruhe Access Structures service and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Abstract A classical relaxor material, PbMg1/3Nb2/3O3 (PMN), has a long history of investigations by Raman and Brillouin spectroscopies. Earlier results on Raman scattering have emphasized a predominant role of disorder and, on the whole, confirmed a model of compositional fluctuations, first suggested by Smolensky and his colleagues. The extensive microstructural studies of PMN in recent years require re-consideration of many conclusions. In the present paper, we initiated analysis of rather complex Raman scattering in order to reach a definite agreement with the recent direct microstructural studies. Different unambiguous features were analyzed in light of polarization measurements, a breakdown in the Raman selection rules, assignment of modes consistent with the Fm3m space group, the mode behavior for some ion substitutions, the key role of the high temperature transformation of the spectra in explaining the origin of Raman active modes, and some other aspects. The behavior of optical phonons is predominantly determined by nanoscale ordering into clusters. However, the evolution to a ferroelectric state affects optical phonons very little. Brillouin scattering gives valuable information about the transition dynamics. The hypersonic damping exhibits a pronounced anomaly at 210K. in the range of a frustrated ferroelectric transition where an anomalous response of other characteristics appears only in an external electric field. Finally, a careful analysis of the Brillouin and Raman spectra of PMN leads to detection of a central peak in light scattering. Quasi-Rayleigh scattering reveals the most important dynamic features in the unique evolution of PMN to a ferroelectric state. Comparison of PMN and some other closely related materials, such as PbSc1/2Ta1/2O3 (PST) and Na1/2Bi1/2TiO3 (NBT) gives evidence of a broad pretransitional range in relaxors with competing interactions between a ferroelectric ordering and another structural transition that develops at higher temperatures. Key Words: Relaxor ferroelectricsphase transition dynamicsRaman scatteringBrillouin scatteringRayleigh scattering
A detailed lattice-dynamic investigation on the relaxor ferroelectric PMN was started to search for "additional" modes (dispersion curves). But the results are complex with 4 branches observed below 6.5 THz, a broad unresolved continuum between 6.5 and 12 THz, a well defined excitation at 13.4 THz with longitudinal and transverse character and further weak signals above 16 THz. Possible effects caused by disorder are discussed.
Low-temperature dielectric and pyroelectric properties were investigated for filled and unfilled tungsten bronze (TB) crystals, i.e., (Sr0.61Ba0.39)5Nb10O30, (K0.5Na0.5)1.0(Sr0.75Ba0.25)4.5Nb10O30, K5.80Li3.82Nb10.12O30, and K5.20Li2.34Nb10.88O30 with the spontaneous polarizations along the c axis at room temperature except for the last one. In all samples, transverse dielectric constant along the a axis showed a universal dielectric dispersion in the low-temperature range resembling a diffuse phase transition. Characteristic relaxation times obtained from the dielectric loss peaks followed the Arrhenius law, signifying thermal activation processes. The distribution of relaxation times seems to be caused by the distribution of activation energy, which has been successfully obtained by scaling the temperature- and frequency-dependent dielectric losses. This broadening may be attributed to the intrinsic randomness due to the charge disorder and quenched random fields caused by the unfilled structure and the off-stoichiometry of the TB compounds. Observed low-temperature dynamics were isotropic in the ab plane, and were insensitive to the poling conditions, degree of disorder, and high-temperature phase transitions. Structural phase transition accompanying a polarization tilt from the c axis toward the [110] axis, which was suggested to be the origin of the low-temperature anomalies, was not confirmed in our study. Some dynamics which are still active in the ferroelectric phase, like the concerted rotations of the oxygen octahedra, have been suggested as one of the possible origins of the observed phenomena.
The relaxor transition in a disordered lead scandotantalate ``virgin'' single crystal has been studied by measuring the ${}^{45}\mathrm{Sc}$ NMR spectra and spin-lattice relaxation rates. The observed spectra can be decomposed in a narrow $1/\stackrel{\ensuremath{\rightarrow}}{2}\ensuremath{-}1/2$ central part and a broad background due to the satellite transitions. The data demonstrate that the macroscopic cubic symmetry is locally broken and that the Sc electric quadrupole coupling constant amounts to about 12 MHz. The local polarization distribution function and the temperature dependence of the Edwards-Anderson order parameter have been determined and can be well described by the recently proposed spherical random bond--random field model.
We report on the results of studies of dielectric properties of loparite-(Ce), a naturally occurring member of the perovskite-type family of materials, in the temperature range of 80–400 K. A strong frequency dispersion attributable to disorder and a dielectric anomaly have been observed in the vicinity of T = 157 K. The behavior of the inverse dielectric permittivity 1/ε′(T) has been found to be well described by the Curie–Weiss law with parameters C = 2.2 × 105 K−1 and Tm = 157 K. Studies of a dielectric hysteresis demonstrated the presence of ferroelectric loops below Tm ≈ 157 K, which points to the existence of a ferroelectric phase transition at Tm. The behaviors of spontaneous polarization, remanent polarization, and coercive field indicate that the ferroelectric phase transition is of the first-order type.
Raman light scattering studies of lattice dynamics of single crystals of relaxor ferroelectric PbNi1/3Nb2/3O3 (PNN) in the temperature range 586–96 K are presented. The measurements revealed the evolution of polarized spectra from the well-known spectra typical of cubic relaxor ferroelectrics in paraphase to more complex ones at low temperatures. During the temperature evolution new lines appeared in the Raman scattering spectra. As shown by the group-theory analysis of the experimental spectra, a cubic phase with the space group Th3 (Fm3) can exist at room temperature. The PNN Raman spectra in the low- temperature phase are described within the framework of the space group C3v2 (P31m), which agrees with the results of X-ray diffraction analysis [K. Kusumoto, T. Sekiya Ferroelectrics, 240, 327 (2000)].
