Nature of defect structure in CoO

The defect structure in CoO is examined in an embedded-molecular-cluster model. The point-defect model with isolated vacancies on either metal or oxygen sites is evaluated and compared with more complex defect structures. We calculate the electronic structure of 4:1 interstitial defects and some of their aggregates in CoO. The binding energy is determined to reveal the most stable defect structure, which is the 4:1 tetrahedral complex in this case. Mulliken population analysis and volume integration confirm the formation of a Co3+ cation at the tetrahedral site.