Anharmonicity in fluoperovskites

Abstract
From an experimental determination of the temperature and pressure dependence of the R25 soft-mode frequency in RbCaF3, KZnF3 and CsCaF3, it is shown that the overall temperature-dependent shift of the soft mode is mainly due to the self-energy (the purely anharmonic effect) whereas the quasi-harmonic contribution (the thermal expansion effect) is one order of magnitude lower.