Electromigration in transition metals. II. Light interstitials in Cu, Ag, Ni, Pd, Al, V, Nb and Ta

Abstract

For pt.I see ibid., vol.3, p.7307 (1991). The electromigration wind valence of interstitial hydrogen in a series of transition metals is calculated using a state-of-the-art computational scheme accounting for the real band structure and local lattice deformation plus charge transfer in the impurity cluster. A microscopic picture of the oscillatory motion and the mobility of the proton explains the remarkable difference between the wind valence of hydrogen in Nb and Ta. A zero-point motion model explains the H/D isotope effect in the effective valence as observed in many systems. From a comparison of experimental effective valences with calculated wind valences, it is concluded that the direct valence, in systems where the wind valence is not dominant, has a value close to unity. Thermal effects are investigated and shown to be unimportant at moderate temperatures. In addition wind valences of interstitial boron in Pd, carbon in Pd and Nb and oxygen in Nb are presented.