Cation Self-Diffusion and Semiconductivity in NiO

Nickel self-diffusion and semiconductivity in single-crystal NiO have been measured as functions of temperature and O2 pressure over ranges of 1182–1762°C and from one to 5 × 10−7 atm. Atmospheres of pure O2, pure CO2, O2–Ar mixtures, and CO–CO2 mixtures have been used. In pure O2 and in pure CO2 the results can be expressed with a standard deviation of less than 4% by equations of the form D = D°exp(− ED / RT ) and σT = (σT)0exp(− Eσ / RT). In pure O2, D° = (4.8 ± 1.3) × 10−2cm2/sec, ED = 60.8 ± 0.6 kcal/mol, (σT)0 = (7.5 ± 0.8) × 106Ω−1·cm−1°K, Eσ = 24.7 ± 0.2 kcal/mol. In pure CO2, D° = (2.1 ± 0.4) × 10−2cm2/sec, ED = 62.7 ± 0.3 kcal/mol, (σT)0 = (65 ± 11) × 106Ω−1·cm−1/sz/K, Eσ = 36.4 ± 0.6 kcal/mol. Both semiconductivity and diffusion coefficients are proportional to Pβ. For diffusion, β increases with temperature, being 0.16 at 1245°C and 0.20 at 1380°C; for conductivity, β is between 14and16 and decreases with temperature. The results can be interpreted in terms of simple models invoking noninteracting defects. Using these models, approximate values have been calculated for the migration and formation energies of the defects.