Lattice Dynamics and Specific-Heat Data of CsCl, CsBr, and CsI

Abstract

Detailed calculations are presented for the frequency distributions and dispersion curves of the three cesium chloride-structure alkali halides: cesium chloride, bromide, and iodide. Three distinct models have been used: the rigid ion model, the polarization dipole model, and two variations of the deformation dipole model. In each case combined frequency spectra and dispersion curves are presented and detailed critical-point assignments made. Plots of the effective Debye temperature θD as a function of temperature are shown and compared with experiment. In addition, the moment functions of the frequency distributions ωD(n) = [13 (n + 3) μn] / n, where μn is the nth moment of a given distribution, have been computed, and plots of these results show that they provide a better means of discriminating between the various models than the θD curves, but unfortunately, no experimental data exist.