Third-Order Elastic Moduli of Calcium Fluoride

Abstract

The complete set of the room-temperature third-order elastic moduli of Ca${\mathrm{F}}_2$ were determined from the change in the sound velocity under uniaxial compression. The measured values in units of ${10}^{11}$ dyn/${\mathrm{cm}}^2$ are $C_{111}=-124.6\mathrm{}$, $C_{112}=-40.0\mathrm{}$, $C_{123}=-25.4\mathrm{}$, $C_{144}=-12.4\mathrm{}$, $C_{166}=-21.4\mathrm{}$, and $C_{456}=-7.5\mathrm{}$. The experimentally measured third-order elastic moduli are compared with the theoretically calculated ones, and a good agreement is found. Conclusions pertaining to the lattice-force interactions are presented.