First-principles Study of Point Defects in Stoichiometric and Non-stoichiometric Y4Al2O9

By using the first-principles calculation, we studied the mechanisms of point defects in Y4Al2O9 (YAM), a promising ternary oxide with excellent optical and thermal properties. It is found that the predominant native defect species is closely dependent on the chemical potentials of each constituent. In the case of O-rich condition, the oxygen interstitial has the very low defect formation energy, followed by the anti-site defects and Al vacancy; in the case of Al-rich condition, the oxygen vacancy yields the lowest defect formation energy, followed by the anti-site defects and Al interstitial. The present result shows that in all the possible chemical potential ranges, anti-site defects have relatively low defect formation energy and might exist in high concentration in YAM. Furthermore, Al-Y anti-site has relatively lower defect formation energy than the Y-Al anti-site throughout. The behaviors of defect complexes under non-stoichiometric condition, such as the Al2O3 or Y2O3 excess, are also investigated. The results provide helpful guide to optimize the experimental synthesizing of YAM.