Elastic Constants of Barium Fluoride Between 4.2 and 300°K

Abstract

The elastic constants of single-crystal barium fluoride have been determined in the 4.2-300°K temperature range, by an ultrasonic pulse-echo technique. The values of the elastic constants, extrapolated to 0°K, in units of ${10}^{11}$ dyn/${\mathrm{cm}}^2$, are: $c_{11}=9.810\mathrm{}$, $c_{12}=4.481\mathrm{}$, and $c_{44}=2.544\mathrm{}$. The constants $c_{11}$, and $c_{12}$ change by about 10%, while $c_{44}$ hardly changes over the above temperature range. Barium fluoride is found to be mechanically isotropic, the value of the anisotropy factor $2c_{44}{(c_{11}-c_{12})}^{-1\mathrm{}}$ being close to unity between 4.2 and 300°K. A value of 282°K for the Debye temperature at 0°K is computed from the elastic constants. The values of the elastic constants are deduced theoretically from a rigid-ion model, and the results compared with the experimental data.