Electrical conductivity and chemical diffusion coefficient measurements in single crystalline nickel oxide at high temperatures

Abstract

Electrical conductivity measurements on nickel oxide have been performed at high temperatures (1273 K< T< 1673 K) and in partial pressures of oxygen ranging from Po 2 = 1.89 × 10 −4 atm to Po 2 = 1 atm. The po 2 1 n dependence of the conductivity decreases from about 1 4 for Po 2 = 1 atm to smaller values for lower partial pressures of oxygen. The activation enthalpy for conduction increases for decreasing oxygen partial pressures (from 22.5 kcal mol −1 at Po 2 = 1 atm to 26.0 kcal mol −1 for Po 2 = 1.89 × 10 −4 atm). This behaviour can be explained by the simultaneous presence of singly and doubly ionized nickel vacancies, with different energies of formation. Furthermore, chemical diffusion coefficient measurements have been performed in the same temperature range, using the conductivity technique, and leading to the result: D ̃ = 0.244 exp (− 36,600 RT ) cm 2 s −1 .