Elastic constants of barium fluoride from 300 to 1250 K

We have determined all three independent adiabatic elastic constants of single-crystal cubic ${\mathrm{BaF}}_2$, 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 $C_{11}$, ($C_{11}$-$C_{12}$)/2, and $C_{44}$. The results are anomalous at the Faraday temperature of 1230 K for ${\mathrm{BaF}}_2$ which is well below its melting temperature of 1550 K. A large decrease in $C_{11}$ and a smaller decrease in $C_{12}$ are observed near 1230 K, in addition to a nearly linear decrease in the elastic constants with temperature. $C_{44}$ does not seem to deviate much from its general behavior near this temperature. Single-crystal ${\mathrm{BaF}}_2$ is found to be approximately mechanically isotropic over the temperature range of 300 to 1200 K.