Chemical Diffusion in Nickel Oxide

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Abstract
The chemical diffusion coefficient was measured for undoped, single‐crystalline NiO at 900° to 1200°C and within an oxygen partial pressure of 10−5 to 0.21 atm. Electrical conductivity was used to monitor the reequilibration kinetics after the oxygen pressure was suddenly changed over the initially equilibrated NiO crystal. The chemical diffusion coefficient was calculated vs the reequilibration degree indicating the most stable range of investigations. The chemical diffusion coefficient value is virtually the same for the oxidation and reduction experiments, giving, respectively: Dchem.=(1.64 × 10−2) exp[‐(22,480±800)/RT] Dchem.=(9.68 × exp[‐(21,430±2600)/RT] It has been stated that chem is independent of the oxygen pressure and thus of oxide composition. The electrical conductivity depends on the oxygen partial pressure in the power (l/n) = (1/5.45), indicating that doubly ionized cation vacancies are the predominant defects. Deviation from the linear dependence of log α vs logpo2 was observed at −5 atm, indicating formation of anion vacancies of interstitials.