Elastic Constants of CsBr, CsI, RbBr, and RbI

The elastic constants of two body-centered halides, CsBr and CsI, were determined as a function of temperature from 300°K to 73°K. The velocity measurements were obtained with an ultrasonic interferometer constructed according to the design principles of Williams and Lamb. Room temperature constants of RbBr and RbI samples were also measured. The values of $C_{11}$, $C_{12}$, and $C_{44}$ in units of ${10}^{11}$ d/${\mathrm{cm}}^2$ at 22°C for these salts are given in the following table: The temperature dependence of all the cesium salt constants was negative and nearly linear over the temperature range investigated. It was found that with decreasing temperatures $C_{44}$ increased more rapidly than $C_{12}$ for the two cesium salts examined.