Elucidating the unintentional p-type nature of spinel Co3O4: A defect study using ab-initio calculation

Co3O4 is one of the most widely used materials in energy and environmental field due to its unintentional p-type nature, which depends on the preparation conditions. In this study, we investigated the origin of the unintentional p-type conductivity of Co3O4 by calculating all possible intrinsic point defects. We found that the octahedral cobalt vacancy and tetrahedral cobalt vacancy are the sources of unintentional p-type doping. Using charge balance theory, we analyzed the effect of preparation condition on intrinsic defect-induced doping. In most of preparation condition, the formation of these cobalt vacancies plays a dominant role and the spontaneous formation of p-type doping is unavoidable. However, if there is ample oxygen and the temperature is low during the preparation, the unintentional p-type doping can be avoided. This theoretical work on defects provides a crucial clue to optimize Co3O4 for various electrochemical applications.