Soft-mode observation in Li₂Ge₄O₉ phase above room temperature

Abstract

Li2Ge4O9 is known to be a ferroelectric phase with Curie temperature at Tc=-83 (degree)C. In this study, we found both low-frequency phonon and heat-capacity anomalies around 100(degree)C in the Li2Ge4O9 phase, demonstrating presence in a structural phase-transition. The phase transition is probably triggered by regularization of distorted GeO6 octahedra in the paraelectric phase, resulting a new phase consisting of the regular octahedral GeO6 unit, which was supported by in situ emission measurement in the Mn4+-doped phase. It is deduced that the phase transition is more dynamic than ferroelectric phase-transition originating in ordering of the Li ions.