Third-Order Elastic Constants of RbMnF3

The complete set of six third-order elastic constants of RbMn${\mathrm{F}}_3$ has been determined from measurements of hydrostatic-pressure and uniaxial-compression derivatives of natural sound velocities. Measurements were made at room temperature using an ultrasonic pulse-superposition technique. The results are $c_{111}=-18.4\mathrm{}$, $c_{112}=-2.4\mathrm{}$, $c_{123}=+0.4\mathrm{}$, $c_{144}=-0.6\mathrm{}$, $c_{155}=-1.8\mathrm{}$, and $c_{456}=-0.5\mathrm{}$ in units of ${10}^{12}$ dyn/${\mathrm{cm}}^2$. The results are interpreted to mean that the third-order elastic constants are predominantly determined by the Mn-F interaction. The significance of this for the mechanics of RbMn${\mathrm{F}}_3$ is discussed.