DETERMINATION OF THERMODYNAMICS AND KINETICS OF POINT-DEFECTS IN NIO USING THE ROSENBURG METHOD

The Rosenburg method has been used to investigate the deviation from s toichiometry and the defect diffusion coefficient in NiO between 1200 and 1300 degrees C and in the oxygen pressure range 0.05-0.25 atmosphe res. Simple point defect chemistry has been applied to interpret the o xygen pressure and temperature dependence of the data. The formation e nthalpy and entropy of nickel vacancies at constant oxygen pressure ha ve been estimated to be 75 kJ/mol and - 15 J/mol K, respectively. The defect diffusion coefficient is essentially independent of the oxygen pressure and the migration enthalpy is determined to be approximately 150 kJ/mol. Combination of the enthalpies for formation and migration of the defects yields an activation enthalpy of 225 kJ/mol for Ni self diffusion. From the oxygen pressure dependence of the nonstoichiometr y, singly charged nickel vacancies have been concluded to be the predo minating point defect. (C) 1998 Elsevier Science B.V. All rights reser ved.