First-principles study of the relative stability of various zirconium hydrides using the special quasirandom structures approach

We present a detailed study on the bulk properties and relative stability of the ordered and disordered phases of zirconium hydrides by using first-principles calculations combined with the special quasirandom structures (SQS) method. The formation energy, density of states (DOS) and elastic constants are calculated to judge the relative stability of these phases. For the ordered phases, the relative stability of different configurations of the γ and δ phase is especially concerned. It is found that the ζ-Zr2H, “diamond-like” γ-ZrH, [111] configurations of the δ-ZrH1.5 and fcc-ZrH2 phase are not stable. For the disordered phases, the SQS method, which is a well-proven method to mimic the random alloys, is used to construct supercells of zirconium hydrides with four structures. It is found that the random alloy gradually transforms from an hcp (solid solution phase) into an fcc (δ phase) and then an fct (c/a < 1, ε phase) phase with the increasing H concentration. The equilibrium states are also determined. The γ phase is energetically not favorable at all H concentrations.