Impurity Diffusion in a Chemical Potential Gradient (II): Iron Tracer Diffusion in Cobalt Oxide in an Oxygen Potential Gradient

Impurity tracer diffusion coefficients for 59Fe in CoO have been measured as a function of the oxygen activity at a temperature of 1200°C. The results can be described by a weak impurity‐vacancy binding at high oxygen potential and a strong binding (Δgv = −0.7 eV) at low oxygen potential. Impurity tracer diffusion has also been measured for 59Fe in CoO which has been exposed to an oxygen potential gradient. In addition to the normal Brownian motion the impurity cations are seen to drift in the crystal as a result of the cation vacancy wind. These results confirm the picture of weak binding at high oxygen potential and strong binding at low oxygen potential. From both experiments it is possible to calculate frequency ratios or directly the frequencies of vacancy jumps.