Ferroelectric Phase Transition in Li₂Ge₇O₁₅

Abstract

The dielectric, ferroelectric, DTA, thermal expansion, Raman scattering and ultrasonic measurements of Li₂Ge₇O₁₅ single crystal have been performed in a wide temperature range including the phase transition point at T_c=283.5 K. It has turned out that Li₂Ge₇O₁₅ undergoes a ferroelectric phase transition of displacive-type and the transition is quite or almost continuous. The Raman spectra obtained support the idea that the phase transition is associated with a soft optic phonon at the Brillouin zone center of the space group Pbcn in the paraelectric phase.