Relation between Fractal Inhomogeneity and In/Nb-Arrangement in Pb(In1/2Nb1/2)O3

Relaxor ferroelectrics show substantial responses to electric fields. The key difference from normal ferroelectrics is a temperature-dependent inhomogeneous structure and its dynamics. The lead-based complex perovskite Pb(In1/2Nb1/2)O3 is an intriguing system in which the inhomogeneous structure can be controlled by thermal treatment. Herein, we report investigations of the phase transitions in single crystals of Pb(In1/2Nb1/2)O3 via changing the degree of randomness in which In and Nb occupy the B site of the ABO3 perovskite structure. We studied the dynamic properties of the structure using inelastic light scattering and the static properties using diffuse X-ray scattering. These properties depend on the degree of randomness with which the B site is occupied. When the distribution of occupied In/Nb sites is regular, the antiferroelectric phase is stabilised by a change in the collective transverse-acoustic wave, which suppresses long-range ferroelectric order and the growth of the inhomogeneous structure. However, when the B site is occupied randomly, a fractal structure grows as the temperature decreases below T*~475 K, and nanosized ferroelectric domains are produced by the percolation of self-similar and static polar nanoregions

Local Linear Coupling between Polarization and Strain in KF-substituted Barium Titanate Crystals Probed by Brillouin Scattering and Dielectric Properties

An elastic anomaly at the paraelectric–ferroelectric phase transition in BaTiO3-related materials is a known precursor phenomenon. However, in the paraelectric phase, this behavior is not expected from the average crystal structure and its origin is still controversial. In this study, to investigate the origin of the elastic anomaly, both elastic and dielectric experiments were performed on 10%KF-substituted BaTiO3, (Ba0.9K0.1)Ti(O2.9F0.1), in which the ferroelectric phase transition is closer to being second order than that in BaTiO3. Around the phase transition, both the elastic and dielectric properties demonstrated clear changes over a wide temperature range. Moreover, a linear correlation between elastic and dielectric properties was confirmed, indicating that the elastic anomaly can be interpreted based on local linear coupling between polarization and strain. This understanding of a phenomenon not expected in homogeneous centrosymmetric crystals is applicable to various perovskite-type ferroelectrics such as KNbO3- and Pb-based relaxor ferroelectrics

Influence of KF substitution on the ferroelectric phase transition of lead titanate single crystals studied by Brillouin light scattering

The elastic properties of KF-substituted perovskite lead titanate (PbTiO3) 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 PbTiO3 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