Diffusion of Transition Metal Ions in Single-Crystal MgO

Abstract

Diffusion coefficients for transition metal ions in single‐crystal MgO have been determined in the temperature range 1000°‐1850°C. from concentration distributions obtained with the aid of x‐ray absorption analysis and electron microbeam probe spectroscopy. The variation of the diffusion coefficients with temperature yields D₀ = 8.83 (10)^‐5, 5.78 (10)^‐5, and 1.80 (10)^‐5 cm²/sec and activation energies for diffusion of 1.81, 2.06 and 2.10 electron volts for Fe²⁺, Co²⁺, and Ni²⁺, respectively. It is found that the activation energy for diffusion increases exponentially with the ratio ionic radius/ionic electronic polarizability for the diffusing cation and that D₀ increases exponentially with the cation radius cubed. This correlation suggests that the diffusion mechanism for all three ions is the same and that self‐diffusion in MgO takes place via the same process.