Elastic constants of barium fluoride from 300 to 1250 K

We have determined all three independent adiabatic elastic constants of single-crystal cubic BaF₂, by an ultrasonic-pulse superposition technique, over the temperature range of 300 to 1250 K. Values of the compressibility, the ultrasonic anisotropy factor, and Cauchy-relation failure over this temperature range are obtained from C₁₁, (C₁₁-C₁₂)/2, and C₄₄. The results are anomalous at the Faraday temperature of 1230 K for BaF₂ which is well below its melting temperature of 1550 K. A large decrease in C₁₁ and a smaller decrease in C₁₂ are observed near 1230 K, in addition to a nearly linear decrease in the elastic constants with temperature. C₄₄ does not seem to deviate much from its general behavior near this temperature. Single-crystal BaF₂ is found to be approximately mechanically isotropic over the temperature range of 300 to 1200 K.