Trends in the electron-phonon coupling parameter in some metallic hydrides

Abstract

Using McMillan’s approximation, the electron-phonon coupling parameter λ has been evaluated for several simple, transition and non-magnetic rare earth metal hydrides. The “electronic” parameter η is obtained in the rigid muffin-tin approximation from our augmented-plane-wave band structure results. The following general trends in the variation of η emerge from these calculations: (1) the Fermi surface states of symmetry about the H site are strongly scattered by the hydrogen potential and the magnitude of the electron-optical phonon matrix element is dominated by the s-p scattering term. For the early transition metal (TM) dihydrides and LaH2, the value of ηH per hydrogen site is found to be small; it is somewhat larger and more or less constant for the other TM dihydrides of the 4d series. This is in contrast to PdH which has a significantly larger value of ηH. Large values of ηH are also obtained for AlH2 and AlH (which can be prepared by ion implantation) making these compounds good candidates for superconductivity. (2) At the metal site is determined essentially by the d-f scattering for the late members of the TM series while the p-d mechanism is important for the early members of the TM series, for LaH2 and particularly for the AlHx system. In most cases, a reduction of ηMetal from its value in the pure metal is obtained for the cubic metal hydrides studied here.