Defect and migration energies of oxygen vacancies in ABO2N (A – Ba, Ca, Sr and B – Ta, Nb) perovskite oxynitrides

Abstract

ABO2N (A = Ca, Ba, Sr & B = Ta, Nb) perovskite oxynitrides are gaining attention as they have band gaps (Eg ∼ 1.8–2 eV) in the visible region. However, these systems are reported to have defects which significantly impact their catalytic behavior. Hence it is essential to understand the defect chemistries of ABO2N systems. In this work, the Mott-Littleton (M-L) method is used to calculate the defect and migration energies associated with oxygen vacancies. For this study, Buckingham potential along with core-shell model has been used for describing the defects in the systems. It is shown that BaTaO2N, BaNbO2N, SrTaO2N and SrNbO2N have low defect energy for oxygen vacancy. Hence, these systems can be explored for solid oxide fuel cell and supercapacitor applications. This is since the presence of oxygen vacancies is reported to improve the ionic conductivity in materials. But for rapid ion/vacancy migration, a low migration barrier is also essential. Hence investigations on oxygen migration energetics are pertinent. The migration energy calculations on ABO2N systems identifies SrTaO2N to be most favorable for applications involving ionic conductivity (e.g. SOFC, gas sensors, supercapacitors). Overall, the work presented here provides specific quasi-chemical pointers relevant for functional applications using oxynitrides.