Nonstoichiometry and hole doping in NiO

We have study by means of DFT+U and thermodynamic calculations the doping response of the p‐type transparent oxide NiO. We have found from the calculated defect formation enthalpies that Ni vacancy, not the O interstitial, is the main source of nonstoichiometry in NiO. On the other hand, the calculated free‐hole concentration at room temperature of pure NiO remains very low compared to the concentration of Ni vacancies; this is due to the too large ionization energy of the Ni vacancy. The free‐hole concentration can be strongly increased by extrinsic dopants with a more shallow donor as it is illustrated for the case of Li.