Elastic Constants of Silver Chloride from 4.2 to 300°K

Abstract

The adiabatic elastic constants of single-crystal AgCl have been determined in the temperature range 4.2 to 300\ifmmode^\circ\else\textdegree\fi{}K by an ultrasonic pulse-echo technique. The values of the elastic constants at 0\ifmmode^\circ\else\textdegree\fi{}K, extrapolated from 4.2\ifmmode^\circ\else\textdegree\fi{}K data, in units of ${10}^{11}$ dyn/${\mathrm{cm}}^{2}$ are: ${c}_{11}=7.590$, ${c}_{12}=3.908$, and ${c}_{44}=0.6894$. The values at room temperature are: ${c}_{11}=5.965$, ${c}_{12}=3.646$, and ${c}_{44}=0.618$. The room-temperature elastic constants are all within 1% of those reported by Arenberg, but differ significantly from data given by Stepanov and Eidus. Of particular interest is the large degree of failure of the Cauchy relation, $\ensuremath{\Delta}={c}_{12}\ensuremath{-}{c}_{44}=+3.219\ifmmode\times\else\texttimes\fi{}{10}^{11}$ dyn/${\mathrm{cm}}^{2}$ at 0\ifmmode^\circ\else\textdegree\fi{}K, and the large discrepancy between the infrared lattice resonance frequency calculated from the elastic constants and that observed experimentally by other investigators. These two facts, coupled with the large temperature dependence observed for the elastic constants, indicate considerable anharmonicity in the lattice potential of AgCl. The Debye characteristic temperature derived from the 0\ifmmode^\circ\else\textdegree\fi{}K elastic constants ${{\ensuremath{\Theta}}_{0}}^{\mathrm{e}1}$ is 161\ifmmode^\circ\else\textdegree\fi{}K according to Betts et al., 165\ifmmode^\circ\else\textdegree\fi{}K according to Anderson, and 164 and 139\ifmmode^\circ\else\textdegree\fi{}K according to two approximations given by Fedorov.