Thermodynamics and Kinetics of Point Defects in Nonstoichiometric Nickel Oxide

The deviation from stoichiometry and chemical diffusion in metal-deficient nickel oxide have been studied as a function of temperature (1073-1673 K) and oxygen pressure (10-10 5 Pa), using microthermogravimetric techniques. It has been found that the nonstoichiometry, y, in Ni 1 - y O is the following function of temperature and equilibrium oxygen pressure: y =0.153 .p 1 / 6 O 2 . exp (80kJ/mol RT), clearly indicating that the predominant defects in this oxide are non-interacting, doubly ionised cation vacancies and electron holes randomly distributed in the crystal lattice. Re-equilibration rate measurements of nonstoichiometry have shown that the vacancy diffusion coefficient, Dv, being the direct measure of defect mobility, does not depend on their concentration and is the following function of temperature: Dv = 0.062 exp (-152KJ/mol RT). Using both these results the self-diffusion coefficient of cations, D N i , in Ni 1 - y O has been calculated as a function ofT and p(O 2 ): D N i = 9.49 . 10 - 3 . p 1 / 6 O 2 . exp (232kJ/mol RT), being in excellent agreement with experimental results obtained on single crystalline material.