HYDROGEN SITE OCCUPATION IN YPD3 WITH L1(2) STRUCTURE

Hydrogen site occupation in a binary metal compound of YPd3 with L1(2) structure is studied experimentally and theoretically. In contradicti on to the semiempirical heat of the formation model, which predicts th e interstitial site preferably occupied by hydrogen atoms in intermeta llic compounds, the present neutron-diffraction study reveals that the hydrogen atoms occupy preferentially the characteristic interstitial site surrounded by six Pd atoms rather than the interstices surrounded by two Y and four Pd atoms. This result is confirmed by the first-pri nciples calculations based on the local-density-functional theory. The difference in the electronic interactions between hydrogen and host a toms is shown to be largely responsible for the occupation of the spec ified interstitial sties by hydrogen in intermetallic hydride.