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 ${\theta }_D$ as a function of temperature are shown and compared with experiment. In addition, the moment functions of the frequency distributions ${\omega }_D\mathrm{(n)\hspace{0.17em}=\hspace{0.17em}[}\frac{1}{3}{\text{\hspace{0.17em}(n\hspace{0.17em}+\hspace{0.17em}3)\hspace{0.17em}μ}}_n{]}^{\mathrm{\hspace{0.17em}/\hspace{0.17em}n}}$ , where ${\mu }_n$ is the $n$ th 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 ${\theta }_D$ curves, but unfortunately, no experimental data exist.