Isotope effect for cation diffusion in CoO

Abstract

The simultaneous diffusion of /sup 55/Co and /sup 60/Co has been measured in CoO as a function of equilibrium oxygen pressure in the range 10/sup -9/ < P/sub O/sub 2// < 1 atm at 1200/sup 0/C. The scope of the log D/sub Co/* vs log P/sub O/sub 2// plot changes from a value of about 1/4 at high P/sub O/sub 2// to about 1/5 at low P/sub O/sub 2// in agreement with the extensive measurements of Dieckmann. The isotope effect is independent of P/sub O/sub 2//, which suggests that diffusion by defect clusters, interstitial Co ions and impurity-induced defects is not important in the present measurements. Conductivity diffusion, stoichiometry, and isotope-effect results are consistent with diffusion by neutral, singly charged, and doubly charged vacancies; the relative contributions from the various vacancies varies with P/sub O/sub 2//.