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Many mixed ionic/electronic conductors (MIECs) applied in fuel cellelectrodes can be considered as alloys between perovskite oxides and orderedoxygen vacancy compounds. For example, in the model MIEC (STF), low oxygendiffusion barrier exist in SrTiO3 lattice, when it has been mixed with SrFeO2.5with intrinsic oxygen deficiency, the ionic conductivity can be greatlyimproved. Meanwhile, the electronic conductivity can be optimized bycontrolling the defect chemistry of the alloy. However, the configurationalspace is too large in such alloys so that it is difficult for direct atomicmodeling, which hinders in-depth understanding and predictive modeling. In thiswork, we present a cluster expansion model to describe the energetics of thedisordered SrTiO3/SrFeO2.5 alloy within the full solid solution compositionspace Sr(Ti1-x,Fex)O3-0.5x (0<x<1). Cluster expansion Monte Carlo simulationshave been performed to search the lowest energy atomic configurations andinvestigate the origin of lattice disorder. With representations of realisticconfigurations, the electronic structures of such alloys at differentstoichiometry have also been examined. We find that the band gap evolution withcomposition calculated using our atomic model is consistent with experimentmeasurement. Meanwhile, the band edge analysis elucidate that electronicconductivity within such alloy can be facilitated by the Fe/Ti cation disorder.Taking SrTiO3/SrFeO2.5 alloy as an example, the generalized computationalframework applied here can be extended to other relevant MIEC material systems.

Structural Disorder and Electronic Structure in Alloyed SrTiO3/SrFeO2.5 Compounds: A Theoretical Study