Abstract
The effects of piezoelectric coupling between the acoustic and soft optic modes in 2% barium-doped lead germanate are studied using Brillouin light-scattering techniques over a wide range of temperatures from about 120 to 480 K, including the ferroelectric phase transition near 426 K. Anomalies in the velocity and absorption of longitudinal acoustic waves are observed near the phase transformation temperature. The results are used to deduce the linewidth of the overdamped soft-optic-mode response and the piezoelectric coefficient a31. Comparisons are made with results from pure lead germanate.