Thermodynamics and Kinetics of Point Defects in Nonstoichiometric Nickel Oxide

Department of Solid State Chemistry, Faculty of Materials Science and Ceramics, AGH University of Science and Technology, al. A. Mickiewicza 30, 30-059 Krakow, Poland (Received October 4th, 2004; revised manuscript November 19th, 2004) 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 (10-105 Pa), using microthermogravimetric techniques. It has been found that the nonstoichiometry, y, inNi1-yOis the following function of temperature and equilibrium oxygen pressure: y = 0.153.pO1/6 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,DNi, inNi1-yOhas been calculated as a function of T and p(O2): DNi = 9.49.10-3.pO 1/6 2 .exp ( - 232kJ/mol RT) , being in excellent agreement with experimental results obtained on single crystalline material.