Thermoelastic Properties of Cadmium Fluoride

The second-order elastic moduli, as well as their temperature and pressure derivatives, and the thermal expansion of single-crystal Cd${\mathrm{F}}_2$ were determined at room temperature. The values of the elastic moduli (in units of ${10}^{11}$ dyn/${\mathrm{cm}}^2$) are $c_{11}=18.270\mathrm{}$, $c_{12}=6.674\mathrm{}$, and $c_{44}=2.175\mathrm{}$. The measured values of the temperature derivatives (in units of ${10}^{-4\mathrm{}}$ ${\mathrm{deg}}^{-1\mathrm{}}$) are $\frac{d\ln c_{11}}{\mathrm{dT}}=-3.71\mathrm{}$, $\frac{d\ln c_{12}}{\mathrm{dT}}=-5.08\mathrm{}$, and $\frac{d\ln c_{44}}{\mathrm{dT}}=-5.33\mathrm{}$; the pressure derivatives are $\frac{d{c}_{11}}{\mathrm{dP}}=7.11\mathrm{}$, $\frac{d{c}_{12}}{\mathrm{dP}}=5.52\mathrm{}$, and $\frac{d{c}_{44}}{\mathrm{dP}}=1.35\mathrm{}$; the thermal expansion is 2.2×${10}^{-5\mathrm{}}$ ${\mathrm{deg}}^{-1\mathrm{}}$. From the elastic data, a Debye temperature of 328°K was deduced. The experimentally measured values of $c_{44}$ and the pressure derivatives were compared with theoretically calculated ones. Good agreement was found for the pressure derivatives, while a large discrepancy for $c_{44}$ was noted. The possible reasons for these correlations and the conclusions pertaining to the lattice interactions in Cd${\mathrm{F}}_2$ are discussed.