Acoustic anomalies and central peak in SrBi2Ta2O9 single crystals studied by micro-Brillouin scattering

Acoustic properties of layered perovskite SrBi2Ta2O9 (SBT) single crystals were investigated by micro-Brillouin scattering. Two elastic stiffness coefficients, c(33) and c(44), defined within the pseudotetragonal crystallographic axes, and the corresponding sound velocities were determined in the temperature range between 290 and 773 K. The longitudinal sound velocity propagating along the pseudotetragonal c axis was found to be very small, which can be related to the weak interlayer bonding of SBT. The corresponding c(33) shows marked softening on approaching the ferroelectric phase transition temperature T-c around 600 K from both high- and low-temperature sides. The hypersonic attenuation increases markedly around T-c, which seems to reflect not only the bilinear coupling between the order parameter and the strain in the ferroelectric phase, but also the electrostrictive coupling in the paraelectric phase. Furthermore, a quasielastic central component was observed near T-c, which is believed to be partly responsible for the change of the low-frequency dielectric permittivity at T-c, besides the contributions from the soft mode and the low-frequency dielectric dispersion. (C) 2002 American Institute of Physics.