First-principles energetics calculations were performed to investigate the structures and relative stabilities of six low millerindex surfaces of orthorhombic YAlO 3 (YAP). The stoichiometric YAP ( 100) and ( 001) were predicted to have the lowest surface energies of 1.91 and 1.96 J/m 2 , respectively. Using a thermodynamic defect model, non-stoichiometric YAP surface energies were further predicted as a function of P O 2 (P O 2 < 1 atm ) and temperature (T). All the results were combined to construct the surface phase diagrams at T = 300 and 1400 K, revealing the strong correlation of the surface stabilities of YAP with its surface stoichiometry.

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