Interstitial sites in the hydrogen-inactive intermetallic compounds ZrPd₂ and UPd₃

The possible interstitial sites for hydrogen occupation in the intermetallic lattices of ZrPd₂ (MoSi₂ tetragonal structure type) and UPd₃ (Ni₃Ti hexagonal structure type) were identified by their Wyckoff notation and characterized by the metal atoms on the polyhedron vertices. Interstitial hole sizes and intersite distances were also calculated utilizing lattice constants and estimated atomic metal radii. It is concluded that hydrogen absorption is not restricted by geometrical factors imposed by empirical and theoretical criteria for the minimum hole size and intersite distance. The hydrogen inertness of the ZrPd₂ and UPd₃ compounds is discussed from the point of view of their large stabilities and the recently found correlations between bonding strengths and hydrogen absorption.