OXYGEN AND NITROGEN DIFFUSION IN TITANIUM NITRIDE

Diffusion of oxygen and nitrogen in titanium nitride was studied using the projector augmented-wave method combined with transition state theory. Atomic migration energies were calculated for two diffusion mechanisms (interstitial and vacancy ones). It was found that the oxygen migration energy in the case of the interstitial mechanism is ~0.3 eV lower than that through nitrogen vacancies, while the indirect mechanism through the position in the center of a cube formed by titanium and nitrogen is more preferable. Estimation of the temperature-dependent diffusion coefficient of oxygen and nitrogen in titanium nitride for two mechanisms showed their strong dependence on the concentration of thermal vacancies. It was shown that the interstitial mechanism of nitrogen diffusion occurs at temperatures below 1500°C and the vacancy mechanism prevails at high temperatures, while the calculated activation energies and diffusion coefficients are consistent with experiment. The obtained values of the oxygen diffusion coefficient for both mechanisms at high concentrations of constitutional vacancies are comparable with the experimental values for TiO2, and the values obtained at low concentrations remain several orders of magnitude higher than in Al2O3.