Elastic constants of palladium and $\beta$-phase palladium hydride between 4 and 300 K

Elastic constants of palladium and palladium hydride in the $\beta$ phase (Pd${\mathrm{H}}_{0.66}$) have been measured on single-crystal samples in the temperature range of 4-300 K. The results obtained in palladium agree with previous measurements. The anomalous temperature dependence of the shear constant $C_{44}$ in palladium is found to be absent in the hydride. The values of the adiabatic elastic constants $C_{44}$, $\frac{1}{2}(C_{11}-C_{12})$, and $\frac{1}{2}(C_{11}+C_{12}+2\mathrm{}{C}_{44})$ in Pd${\mathrm{H}}_{0.66}$ in units of ${10}^{12}$ dyne/${\mathrm{cm}}^2$ are, respectively, 0.691, 0.327, and 2.633 upon extrapolation to absolute zero. The Debye temperature of the hydride calculated from its elastic constants is 285 K at low temperature. The hydride elastic constants did not show any pronounced anomaly over the "50-K transition" temperature region.