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

The surface structures and relative stabilities of low miller-index surfaces of epsilon-ZrH2 and gamma-ZrH have been investigated as a direct function of environmental conditions (hydrogen partial pressure pH(2) and temperature T) from the first-principles thermodynamic calculations. The results were used to construct their surface phase diagrams for a wide p(H2) range at T = 300 and 900K. The g-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 1.2e1.3 J/m(2). For p(H2) > e(-53) at 300K (or p(H2) > e(-5.3) at 900K), gamma-ZrH can no longer be stable but have the tendency to transform into e-ZrH2, by consistently absorbing H from the gaseous environment. The epsilon-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/m(2). (c) 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.