Superconductivity in Metal Hydrides
Using the results of a systematic study of the electronic structure of stoichiometric metal hydrides the electron-phonon coupling parameter has been evaluated, within the McMillan approximation, for a series of mono and dihydrides. The electronic term n is calculated using the rigid-ion approximation while experimental data are used to estimate the phonon contribution. Systematic trends are observed in the variation of η due to the metal site M and hydrogen site H. Sizeable values of ηH are obtained for the metal hydrides with filled d bands such as PdH; ηH is also large when a metal-hydrogen antibonding band crosses the Fermi level, a case which happens in AlH and may happen for unstable dihydrides. The electronic contribution ηM is found to be small for all stable mono and dihydrides such as PdH, NiH, ZrH2 NbH2, LaH2 and for FeTiH and FeTiH2 although nothing prevents in principle ηM from being large in some metal hydrides, as the Fermi level sweeps through the metal d band. A good agreement is obtained with available experimental data for the occurrence of superconductivity in the hydrides under study.
KeywordsFermi Level Metal Hydride Phonon Coupling Phonon Contribution Palladium Hydride
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