Charge and ion transport in NiO and aspects of Ni oxidation from first principles

Motivated by relevance to Ni metal oxidation, electronic and ionic transport properties of bulk NiO were calculated from first principles with the GGA+U formalism. The calculations suggest that bulk NiO is a p-type oxide with Ni vacancies as the majority defect and hole donating species, consistent with current understanding. Calculated energy barriers for diffusion of interstitial Ni and O and their corresponding vacancy partners show that while generally lower for interstitials, their formation energies are much larger. The small electron polaron (e ^-) in the form of Ni ⁺ was directly computed. Its formation energy is lower than that of a hole small polaron, and its diffusion activation energy is significantly lower than those calculated for the ionic defects. Calculation of the electrical field local to structurally specific heteroepitaxial Ni/NiO interfaces shows that the field strength is lowest for Ni(111)/NiO relative to both Ni(100)/NiO and Ni(110)/NiO, suggesting a low driving force for electron injection into NiO from Ni(111) in general consistency with the highest corrosion resistance observed for this surface.