Tetrahedral occupancy in the Pd-D system observed by in situ neutron powder diffraction

Abstract

The crystallography of the Pd-Dx system has been studied by in situ neutron powder diffraction at 309 ì in the supercritical region, and, after quenching in the pure ߠphase to 50 ì in the two-phase region at 50 î Rietveld profile analysis of the supercritical diffraction patterns showed that 14% of D interstitials were occupying tetrahedral interstices, in sharp contrast to previous studies at lower temperatures. Tetrahedral occupancy was maintained through the two-phase region at 50 î These results are discussed in the light of first-principles total-energy calculations of hydrogen states in palladium.