Mechanism of fast lattice diffusion of hydrogen in palladium; Interplay of quantum fluctuations and lattice strain

Kimizuka, Hajime*; Ogata, Shigenobu*; Shiga, Motoyuki   

To understand the mechanism of high diffusivity of hydrogen in palladium, we have studied the process of fast diffusion of interstitial H in face-centered cubic Pd, based on a first principles simulation taking account of quantum mechanical nature of both electrons and nuclei under finite strains. The simulated results revealed that the activation barrier for hydrogen migration was drastically increased with decreasing temperature owing to nuclear quantum effects on the octahedral sites. However, under the lattice expansion, nuclear quantum effects became less important since the tetrahedral site is stabilized. This implies that the diffusion mechanism gradually changes from quantum-like to classical-like as the strain is increased.