An ab initio study of the oxygen defect formation and oxide ion migration in (Sr1-xPrx)2FeO4±δ

Abstract

The Sr n+1 Fe n O 3n+1 Ruddlesden-Popper (RP) perovskite family displays promising oxygen permeability and serves as a host stoichiometry for the design of solid oxide electrode materials. A strategy to tune electronic and ionic properties is the introduction of substitutional dopants like Pr 3+ to the A-site. In this study, we investigate the bulk structural, electronic, and oxygen migration properties for the n = 1 RP perovskite (Sr 1-x Pr x ) 2 FeO 4± δ (x = 0, 0.125, 0.25, 0.375, and 0.5). The oxygen partial pressure is adjusted to elucidate how anodic and cathodic operating conditions influence the formation of oxygen defects. Under anodic conditions, the oxygen vacancy is the dominant oxide defect for all dopant-configurations. Under cathodic conditions, oxygen vacancy defects dominate for configurations from x = 0 to x = 0.375 while the oxygen peroxide interstitial defect becomes the primary defect for x = 0.5. Next, we examine the relationship between Pr 3+ concentration, iron oxidation state, and charge compensation with defect formation to explain the trends in vacancy and peroxide interstitial formation energies. Results clarify the role of lanthanide A-site substitutional dopants on the electronic conductivity and oxide defect formation and migration in Sr-based RP perovskites. These atomic-scale insights suggest design directions for RP perovskites in SOFCs. • Doping strategy of Sr 2 FeO 4 with Pr 3+ for targeted electronic and ionic properties. • Mechanism of vacancy defect formation outlined in terms of charge delocalization. • Mechanism of interstitial defect formation outlined in terms of A-site identity. • Studied all non-symmetrical vacancy-mediated migration paths for given Pr 3+ value.