Electronic structure and electron-phonon coupling in stoichiometric and defective hydrides MPdH3 (M=Ca, Sr, Eu, Yb).

Abstract

On the basis of electron transfer from the divalent element to the ${\mathrm{PdH}}_{3}$ entities, the perovskite structure M${\mathrm{PdH}}_{3}$ (M=Sr, Eu, Yb) are expected to have similar electronic states at the Fermi energy as superconducting Pd-${\mathrm{H}}_{\mathit{x}}$ and Pd--noble-metal--${\mathrm{H}}_{\mathit{x}}$ and thus could be potential candidates for superconductivity. With this motivation, we have investigated the electronic structure and some aspects of the electron-phonon coupling in these hydrides using the ab initio augmented plane-wave method, and the results of the energy bands, the total and partial wave analysis of the density of states, and the electronic contribution, ${\mathrm{\ensuremath{\eta}}}_{\mathrm{H}}$ to the electron-phonon coupling are presented. Similar studies for the hydrogen defective material ${\mathrm{CaPdH}}_{2}$ are also included. We have found that all these compounds are metallic with essentially filled Pd-d bands and a small density of states at Fermi level as in PdH. Nevertheless, the calculated values of ${\mathrm{\ensuremath{\eta}}}_{\mathrm{H}}$, which govern the contribution of the hydrogen atoms to the electron-optical phonon coupling parameter \ensuremath{\lambda}, although sizeable, are lower than in PdH. This would indicate that these compounds, if superconducting, would have lower values of the superconducting transition temperatures ${\mathit{T}}_{\mathit{c}}$ than in PdH. \textcopyright{} 1996 The American Physical Society.