Positron studies of metal hydrides

摘要

Angular correlation of the two photons emerging from positron annihilation in LaH2.71, YH2.36, EuH2.0, and EuH2.73have been measured. By comparing with other published data it can be concluded that all heavy rare earth hydrides at high hydrogen concentrations exhibit almost triangular shaped angular correlation curves with an exceptionally large Gaussian component. Results are consistent with charge transfer to the hydrogen site and contribution from interference between the metal and hydrogen atoms. Mixed valency is believed to play a role in europium hydrides.