Local Diffusion and Tunneling of Trapped Hydrogen in Metals

Abstract

Hydrogen interstitials bound by impurity atoms in metals can locally diffuse or tunnel between equivalent trap sites around its impurity-atom trap center. For hydrogen trapped by N or O interstitials in Nb, these local dynamics were studied in specific heat and neutron scattering measurements demonstrating the existence of low-temperature tunneling eigenstates for hydrogen in metals. Hydrogen impurity-atom complexes represent a unique system for studies of the dynamical behavior especially in the low-temperature range where, for impurity-free metals, hydrogen diffusion or tunneling can not be experimentally investigated because of precipitation. They offer also the possibility to study for the first time the transition from coherent to incoherent quantum transport of hydrogen in metals by powerful experimental techniques such as neutron spectroscopy.