The 50K transition in palladium hydrogen alloys. II. Specific heat and thermal relaxation

For pt.I see ibid., vol.6, p.2219 (1976). A re-investigation of the specific heat anomaly at 50K in Pd-H (for an alloy with H/Pd=0.63) has shown that the magnitude of the anomaly depends on the rate of temperature change used in the specific heat measurement-the slower the rate, the larger the anomaly. Measurements of the spontaneous heat released by the Pd-H sample after sudden cooling to temperatures in the 50K region have yielded information on a thermal relaxation in Pd-H with 'fast' and 'slow' relaxation times and a common activation energy of (1.98+or-0.03)*10 3 J g-atom -1 of H. The measurements indicate that for the 50K transition in Pd-H, diffusion of the hydrogen atoms is an important, and possibly the controlling, step.