Isotope Effect for Cation Self-Diffusion in CoO Crystals

Abstract

Diffusion of ${}_{}{}^{60}{}_{}{}^{}\mathrm{Co}$ in CoO crystals has been measured in the temperature range from 963 to 1638°C in air by the standard tracer-sectioning technique. The temperature dependence of the diffusion coefficient $D$ is given by $D=(5.0\mathrm{}\pm 0.4)\times {10}^{-3\mathrm{}}{e}^{-\frac{(38390\mathrm{}\pm 230)}{\mathrm{RT}}}$ ${\mathrm{cm}}^2$/sec. The isotope effect for cation self-diffusion was determined by simultaneous diffusion of ${}_{}{}^{55}{}_{}{}^{}\mathrm{Co}$ and ${}_{}{}^{60}{}_{}{}^{}\mathrm{Co}$ tracers in CoO crystals. The strength of the isotope effect, defined by $E_{60}=\frac{[1-(\frac{D_{60}}{D_{55}}\left)\right]}{[1-{\left(\frac{m_{55}}{m_{60}}\right)}^{\frac{1}{2}}]}=f\Delta K$ was 0.582±0.009, independent of temperature in the range from 1081 to 1411°C. This result is consistent with cation self-diffusion by a vacancy mechanism only, and $\Delta K=0.746\mathrm{}\pm 0.012$.