Local Linear Coupling Between Polarization And Strain In Kf-Substituted Barium Titanate Crystals Probed By Brillouin Scattering And Dielectric Properties

The elastic anomaly in the paraelectric-ferroelectric phase transition in BaTiO3-related materials is a known precursor phenomenon. However, in the paraelectric phase, this behavior is unexpected from the average cubic 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 conducted on 10%KF-substituted BaTiO3, (Ba0.9K0.1)Ti(O2.9F0.1) crystals, in which the ferroelectric phase transition is closer to being the second order compared with that in BaTiO3. Around the phase transition, both elastic and dielectric properties demonstrated clear changes over a wide temperature range. Moreover, a linear correlation was confirmed between the elastic and dielectric properties, indicating that the elastic anomaly can be interpreted based on the local linear coupling between polarization and strain. This understanding of a phenomenon unexpected in homogeneous centrosymmetric crystals applies to various perovskite-type ferroelectrics, such as KNbO3 and Pb-based relaxor ferroelectrics.