Atomic-scale Ab-initio study of the Zr-H system: I. Bulk properties

Bulk proper-ties of the Zr-H system were studied in the framework of the density functional theory. The local density approximation (LDA) is found to be insufficient for a proper description of interactions between Zr and H atoms and the generalized gradient approximation (GGA) is required. In alphaZr, H atoms preferentially occupy tetrahedral (T) sites at low temperatures, and can be regarded as being independent of each other up to very short distances, except for repulsive interactions between dumbbells in the same interstitial site. The Zr density of electronic states is perturbed by the presence of H, which induces the emergence of localized states. H diffusion occurs along the (c) over right arrow axis preferentially in octahedral (O) sites, and in the basal plane by alternate jumps into T and O sites. In the gamma(ZrH), delta (ZrH1.5) and epsilon(ZrH2) hydrides, H-H interactions cannot be neglected, the nearly equal formation energies of these compounds indicate that their relative stabilities probably depend on mechanical and thermal contributions to free energies, and in fee Zr, H atoms tend to adopt planar arrangements for compositions close to ZrH. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.