A quantitative systematization of hydrogen-induced changes in Debye temperatures of metals

Abstract

Nuclear resonance scattering of γ rays has recently been used to obtain information on the Debye temperatures θ D , of metal hydrides. In particular the contribution of nickel to the θ D of Mg 2Ni, LaNi 5 and their hydrides was estimated. It was assumed that the different behaviour of θ D for nickel in the two cases ( i.e. an increase upon hydrogenation in Mg 2Ni and no change in LaNi 5) could be related to the different stabilities of the two hydrides. Consequently an empirical relationship connecting the Debye temperatures θ M and θ H of a metal and its hydride respectively with the heat ΔH f of formation of the hydride was derived from experimental data reported by various investigators. It appeared, however, that two ambiguous calculating procedures were used to derive the θ H values. One of these procedures was used consistently in the present work for all the metal-hydrogen systems and the original phenomenological rule was changed accordingly. The qualitative theoretical considerations preceding the derivation of the empirical relation are briefly presented. Some experimental data recently reported in the literature are discussed in terms of the proposed empirical rule. In particular the obvious exceptions associated with the group IVa metal hydrides TiH x and ZrH x are attributed to the Jahn-Teller effect in these systems.