The temperature dependence of the infrared reflection spectra in the fluoperovskites RbCaF3, CsCaF3and KZnF3

Abstract
Infrared reflection spectra of the fluoperovskites RbCaF3, CsCaF3 and KZnF3 have been measured in the range 50-4000 cm-1 at several temperatures. A systematic study of the temperature dependence of the TO and LO frequencies, dampings, and oscillator strengths of the three polar phonon modes is reported. The ionic effective charges have been calculated from the TO-LO splittings. A slight increase of the static dielectric constant upon cooling indicates incipient ferroelectric character.