The temperature dependence of the Raman spectra of some alkaline earth crystals with the fluorite structure

Abstract

The temperature dependence of the one-phonon Raman bands in single crystals of CaF₂, BaF₂, SrF₂ and SrCl₂ has been investigated over the temperature range 15-1300K. The frequency shifts and linewidths are calculated according to quasi-harmonic theory. Agreement is satisfactory for T< Theta , the Debye temperature, indicating a two-phonon decay process. A small contribution due to anharmonic effects becomes evident above the Debye temperature for all crystals. The temperature dependence of the Raman-active frequencies is found to increase in the order CaF₂22. Gruneisen parameters are determined and the results compared with pressure dependent measurements of the optical phonon frequencies.