Compton profiles of vanadium and palladium hydrides

Compton profiles for polycrystalline Pd${\mathrm{H}}_{0.72}$, V${\mathrm{D}}_{0.77}$, V${\mathrm{H}}_{0.71}$, Pd, and V have been determined by Compton scattering of 159-keV photons from a ${}_{}{}^{123}{}_{}{}^{}\mathrm{Te}_{}^m{}_{}{}^{}$ source. The difference profiles before and after hydrogen loading are compared to different models for the electronic structure of the hydrides. It is shown that the Compton profile is a sensitive test of the accuracy of various model wave functions for the hydrides. In both palladium and vanadium hydride (deuteride) the anionic model (where it is assumed that the hydrogen forms a negative ion ${\mathrm{H}}^{-}$ in the hydride) does not describe the experimental results. The best agreement with the experimental data for Pd${\mathrm{H}}_{0.72}$, V${\mathrm{D}}_{0.77}$, and V${\mathrm{H}}_{0.71}$ is obtained for a model which is based on band-structure calculations for these hydrides and which takes into account that hydrogen-palladium or hydrogen-vanadium bonding states are created below the Fermi level by the introduction of hydrogen in the host lattice.