Stoichiometric and Nonstoichiometric Surface Structures of Pyrochlore Y2Zr2O7 and Their Relative Stabilities: A First-Principles Investigation

First-principle total energy calculations were performed to investigate the atomic structures and relative stabilities of two low miller-index surfaces of pyrochlore Y2Zr2O7. The stoichiometric Y2Zr2O7 (110) and (100) surfaces were predicted, with lowest formation energies of 1.20 and 1.47 J/m(2), respectively. Based on a thermodynamic defect model, non-stoichiometric Y2Zr2O7 surface energies were further evaluated as a function of environmental oxygen partial pressure (p(O2)) and temperature (T). With all of the results, we were able to construct the surface phase diagrams for T = 300 and 1400 K. The strong correlation between the structural stabilities and the surface stoichiometry was revealed as varying T and p(O2). At a given T, the most stable termination of the (110) surfaces would change from a (Y,Zr)-rich (ns-2Y2Zr6O) to O-rich ones (ns-4O_2 and ns-4O_1) as increasing p(O2), while that of the (100) surfaces would change from the stoichiometric (stoi-1Y1Zr_1) to the O-rich one (ns-5O). The critical p(O2) value for termination transition moves to its higher end as increasing T.