Ab Initio Study of Electron and Hole Polaron Transport in Cobalt(II,III) Oxide Using Oxidation-State Constrained Density Functional Theory

The nature of electron and hole polaron transport inthe mixedvalence cobalt(II,III) oxide Co3O4 in pristineconditions and with an oxygen vacancy are studied using Oxidation-StateConstrained DFT (OS-CDFT). We find that the tetrahedral site repelselectron polarons as hopping from a neighboring octahedral site towardthe tetrahedral site is highly endothermic while hopping away towarda neighboring octahedral site is nearly instantaneous. Hence, electronpolarons travel through bulk Co3O4 using pathwaysthrough only octahedral Co ions. In contrast, while the purely octahedralpathways remain the dominant pathway for hole polaron transport, thepathways involving both the octahedral and tetrahedral sites are stillviable with about two thirds the rate of the octahedral pathways.Moreover, the purely octahedral pathway is enhanced with an oxygenvacancy for both the electron and hole polarons. On the other hand,pathways involving both the octahedral and tetrahedral sites are impededin the presence of an oxygen vacancy for both the electron and holepolarons due to increased magnitude of driving forces.