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 CdF₂ were determined at room temperature. The values of the elastic moduli (in units of 10¹¹ dyn/cm²) are c₁₁=18.270, c₁₂=6.674, and c₄₄=2.175. The measured values of the temperature derivatives (in units of 10^-4 deg^-1) are dlnc₁₁dT=-3.71, dlnc₁₂dT=-5.08, and dlnc₄₄dT=-5.33; the pressure derivatives are dc₁₁dP=7.11, dc₁₂dP=5.52, and dc₄₄dP=1.35; the thermal expansion is 2.2×{}10^-5 deg^-1. From the elastic data, a Debye temperature of 328^∘{}K was deduced. The experimentally measured values of c₄₄ and the pressure derivatives were compared with theoretically calculated ones. Good agreement was found for the pressure derivatives, while a large discrepancy for c₄₄ was noted. The possible reasons for these correlations and the conclusions pertaining to the lattice interactions in CdF₂ are discussed.