Connection between the low temperature acoustic properties and the glass transition temperature of fluoride glasses

Abstract
The variations of the phase velocity and the absorption of longitudinal and transverse acoustic waves of frequencies around 1 GHz have been measured in three fluorozirconate glasses in the temperature range 0.1 K to 1.5 K. The acoustic behaviour at these low temperatures has been ascribed to the existence of two-level systems (TLS). From the measurements, the TLS spectral density and the TLS-phonon coupling constants have been determined. The TLS spectral density has been found to be inversely proportional to the glass transition temperature T g. The TLS-phonon coupling constants vary linearly with T g