Fabrication and Observation of Metastable to Stable Relaxation of Palladium Hydride Thin Films

Abstract

We fabricated metastable palladium hydride by hydrogen ion implantation to a 10 nm-thick Pd film at 7 K, and monitored the hydride formation and relaxation to a stable state by resistivity measurements. By heating the sample, we observed a substantial change in resistivity below 100 K without accompanying hydrogen desorption. While the resistivity change was observed at 80 K for both H and D, it was observed only for H at 6 K. This irreversible resistivity change is attributed to transition from the metastable state to its stable state by hydrogen diffusion. It is considered that hydrogen atoms undergo diffusion thermally at 80 K and by quantum tunneling at 6 K.