Cation Diffusion in Cr₂ O ₃

On employing a sectioning technique with Cr⁵¹ as the tracer, the diffusion of Cr ions in nitrogen‐equilibrated was determined from 1045° to 1550°C. Volume diffusion coefficients in hot‐pressed compacts of three different impurity levels conform to the expression . Additions of and do not cause a significant change. Use of lower density sintered compacts provides erroneous results. Conductivity measurements were performed in nitrogen, argon, and air over a wide temperature range; no dependence on oxygen partial pressure was observed. Calculated cation transference numbers vary from 10⁻³ to 10⁻⁶. Postulating a simplified model for the defect structure of , the activation enthalpy for hole motion is 8.4 kcal mole⁻¹; the enthalpy of defect formation is 91 kcal mole⁻¹; the activation enthalpy for cation motion is about 31 kcal mole⁻¹.