Sr Doping and Oxygen Vacancy Formation in La1-xSrxScO3-δ Solid Solutions: Computational Modelling

Sr-doped lanthanum scandate La1-xSrxScO3-delta (LSS) is a promising perovskite-type material for electrochemical applications such as proton conductors. Oxygen vacancy is a common defect in ABO(3)-type perovskites. It controls ion transport as well as proton uptake. The energetic, structural, and electronic properties of oxygen vacancy in LSS are studied deploying the DFT method with meta-GGA functional. The vacancy formation energies in LSS were calculated for various Sr concentrations. Unlike other perovskites, in this material, the electrons are trapped at the oxygen vacancy site (the F-type centres, common in ionic oxides like MgO and Al2O3) rather than localised on the nearest to the vacancy B-cations. The process of oxygen vacancy formation is considered relative to Sr concentration x and oxygen nonstoichiometry factor delta. Three primary regimes are discussed: (I) localized at the vacancy electrons, x/delta < 2, (II) electron charge balanced system, x/delta = 2, and (III) delocalized electron holes, x/delta > 2. For x/delta >= 2 oxygen vacancy formation energy reaches the saturation level of similar to 3.5 eV, which is potentially beneficial for the proton uptake.