Diffusion of Sr2+ in single crystal MgO

Measurements of the diffusion of Sr²⁺ at tracer concentration in high‐purity single crystal MgO have been made over the temperature range from 1000 to 1600°C. After applying a graphical correction for the effects of a short‐circuiting diffusion component which is also present, the observed diffusion coefficients, D, applicable to lattice diffusion could be fitted by the equation ${\text{D=(6.0 ±}}_{\text{3.8}}^{\text{10.7}}{\text{) × 10}}^{\text{−4}}\exp \text{[−(2.91 ± 0.13)/kT]\hspace{0.17em}}{\mathrm{cm}}^2/\sec$ , where T is the absolute temperature and k is Boltzmann's constant in electron volts per degree Kelvin. The relation of this result to previously found correlations of the activation energy and frequency factor with the radius of the diffusing ion, r, is examined. It is found that D can be expressed as a rapidly varying function of r and T only over a range of r from 0.3 Å to 1.3 Å. This size effect is discussed in relation to that observed in other ionic solids.