Temperature and hydrogen partial pressure dependence of zirconium hydride surface structures and stabilities

Abstract

The surface structures and relative stabilities of low miller-index surfaces of ε-ZrH2 and γ-ZrH have been investigated as a direct function of environmental conditions (hydrogen partial pressure pH2 and temperature T) from the first-principles thermodynamic calculations. The results were used to construct their surface phase diagrams for a wide pH2 range at T = 300 and 900K. The γ-ZrH surfaces tend to be dominated by the Zr-rich (101) with the 101-ns-2Zr1H termination. The surface energy would depend on T and pH2, with a value of 1.2–1.3 J/m2. For pH2 > e−53 at 300K (or pH2 > e−5.3 at 900K), γ-ZrH can no longer be stable but have the tendency to transform into ε-ZrH2, by consistently absorbing H from the gaseous environment. The ε-ZrH2 surfaces tend to be dominated by the stoichiometric (111) facet with the 111-stoi-2H termination and the surface energy of 1.29 J/m2.