Hydrogen diffusion by tunnelling in palladium

Abstract

Diffusion and internal friction data for H in PdH x with 0.1 ⩽ x ⩽ 0.7 fit a simple model of H hopping over and tunnelling through a cosine barrier between octahedral sites. Cold-work on the hydride introduces strains that prevent tunnelling, and the “cold-work” friction peaks indicate that the top of the cosine barrier is at about E a = 315 meV. This potential also gives the correct H oscillation energy E 1 = 56 meV, and the ground state tunnelling ΔE TO/ h = 3×10 4 Hz. We argue that the H self-trapping energy is not important for diffusion by tunneling in PdH x .