Elastic constants of palladium andβ-phase palladium hydride between 4 and 300 K

Elastic constants of palladium and palladium hydride in the β phase (PdH0.66) 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 C₄₄ in palladium is found to be absent in the hydride. The values of the adiabatic elastic constants C₄₄, 1/2(C₁₁-C₁₂), and 1/2(C₁₁+C₁₂+2C₄₄) in PdH0.66 in units of 10¹² dyne/cm² 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.