Prediction on Phase Stabilities of the Zr-H System from the First-Principles

Basic fundamentals governing the hydrogenation of Zr and its alloys have both theoretical and practical importance. In this work, first-principles calculations have been performed to evaluate the relative stabilities of various possible phases in ZrHx(x = 1-2) under different temperatures and pressures. It was predicted that fct-gamma and epsilon phases with various different H-atom configurations can be energetically favorable for ZrHx(x = 1, 1.25 and 1.5), while ZrH(1.75)and ZrH(2)prefer fct-epsilon phase only. Fcc-delta phase is less favored in energy at any H concentrations, but can be mechanically stable in some cases. The thermodynamically stable and metastable phase stability diagrams were then constructed for a wide temperature and H concentration range, to predict the environment-dependent formation of ZrH(x)during hydrogenation.