Theoretical analysis on O vacancy and cation inversion in NiCo2O4

We have implemented polarized density function theory (DFT) on the transition metal d orbitals to explore the effects of oxygen vacancy and cation inversion on properties of NiCo2O4. The results show that NiCo2O4 has ferrimagnetic half-metallic ground states. Oxygen vacancy introduces additional energy levels in the majority spin band gap, which increases the chance of electron transition. In addition, O vacancy only affects the magnetic moment of the neighbor Oct Ni and Oct Co atoms. Calculations on NiCo2O4 with cation inversion confirms that coordinated sites of metal ions affect their spin state and valence, which further influence the conductivity and ferrimagnetic properties. The valence information of metal ions in NiCo2O4 was given. And the increased electron states in top of valence band make great contributions to p-type conductivity of NiCo2O4.