Analysis of the temperature dependence of elastic constants of AgCl

The lattice dynamical properties of Ag halides are markedly different from those of typical ionic solids such as alkali halides. To gain further understanding on the origin of this difference, studies of elastic properties will be valuable. In the present report, the temperature dependence of the second order elastic constants of AgCl has been calculated by using a formula derived from the Murnaghan model of elastic constants. It is shown that the model reproduces the temperature dependence of C11 and C12 found experimentally. However, the calculated values of C44 deviate from the experimental values at high temperatures. The same model applied to NaCl reproduces quite well the temperature dependence over wide range. The result indicates that the model for the elastic constants used widely in the literature should be used carefully. A discussion concerning the microscopic origin of the differences in the behavior between Ag and alkali halides is given.