Elastic Anomaly of the Ferroelectric Phase Transition of Li₂Ge₇O₁₅Studied by the Brillouin Scattering

Abstract

Temperature dependence of the Brillouin scattering spectra of lithium heptagermanate Li 2 Ge 7 O 15 has been observed near the paraelectric-ferroelectric phase transition temperature T C . A longitudinal acoustic mode propagating along the b -axis shows an elastic anomaly in the frequency shift and also in the spectral width. An order-disorder type phase transition mechanism describes the temperature dependence of the elastic anomaly in terms of a piezoelectric coupling below T C . The depolarization field effect is confirmed by comparison with both results on the transverse and longitudinal acoustic modes each other.