The self-diffusion of Ni in undoped and Al-doped NiO single crystals

Abstract

Abstract The 63Ni tracer diffusion coefficient for diffusion in undoped NiO single crystals and crystals doped with 0.17 wt% Al has been measured, at an oxygen pressure of 1 atm in the temperature range 755–1700°C. It has also been measured at 1460° as a function of oxygen pressure in the range. 10−4−1 atm. At temperatures below 1200°C some of the Al dopant was precipitated as NiAl2O4 and the degree of doping was determined by the saturation solubility of Al in NiO. At temperatures above 1200°C defect models assuming either only singly charged Ni vacancies, or both singly and doubly charged vacancies having different diffusion coefficients, were incapablee of a satisfactory interpretation of the. data. It is suggested that this is due to the formation of Ni vacancy-Al complexes having lower mobility than the unassociated Ni vacancies. A model in which singly charged vacancies form associates with Al dopant ions with a binding energy of 1.2 eV is shown to fit the diffusion data in Al-doped Nit) over the. whole temperature range, using reasonable parameters to describe the solubility of Al in NiO.