DIELECTRIC RESPONSE OF ALKALINE EARTH FLUORIDES

The temperature dependence of the low-frequency dielectric response of CaF2, SrF2 and BaF2 over the range 2-350°k is reported, together with the pressure dependence, for hydrostatic pressures up to 5 kbar, at selected temperatures in the range 60 to 350°k. The low-temperature data are used to assess the nature and extent of the electronic structure and interionic forces of the alkaline earth fluorides. The temperature dependence of the dielectric response is found to be due principally to intrinsic volume changes in the crystals rather than to intrinsic temperature changes in the anharmonic contribution. The temperature dependence under constant volume of the anharmonic contribution to the dielectric constant of all three salts exhibits a maximum value near 0·25 θD, where θD is the characteristic Debye temperature. The quasi-harmonic contributions are analysed to determine values for the κ similar, equals 0 longitudinal and infra-red active transverse optic phonon Gruneisen constants.