Third-Order Elastic Moduli of Strontium Fluoride

The complete set of the second- and third-order elastic moduli of single-crystal strontium fluoride was determined from measurements of sound velocity and its changes under uniaxial and hydrostatic compression at room temperature. The values of the measured third-order elastic moduli in units of ${10}^{11}$ dyn/${\mathrm{cm}}^2$ are $C_{111}=-82.1\mathrm{}$, $C_{112}=-30.9\mathrm{}$, $C_{144}=-9.5\mathrm{}$, $C_{166}=-17.5\mathrm{}$, $C_{123}=-18.1\mathrm{}$, and $C_{456}=-4.2\mathrm{}$. The experimentally measured third-order elastic moduli were compared with the theoretically calculated ones, and agreement was found. Conclusions pertaining to the lattice forces interactions in strontium fluoride are presented. The measured values of the third-order elastic moduli are correlated with the thermal expansion.