Cation self-diffusion in single-crystal MgO

Abstract

Cation self-diffusion coefficients have been obtained for MgO in an argon atomosphere over a temperature range 1000–2400°C from concentration gradients determined with the aid of mass spectrometry. The problems associated with use of the short-lived radioisotope 28Mg were avoided by employing the stable isotope 26Mg as a tracer. Samples were prepared utilizing vapor-exchange, thick-film, and semi-infinite source boundary conditions at high, intermediate, and low temperatures, respectively, and were protected from contamination and volatilization by encapsulation in cylinders of pressed MgO powder. No significant difference in transport behavior was noted between crystals of moderate quality and those of the highest purity presently available. The temperature dependence of the diffusion coefficients may be represented by an activation energy of 2.76±0.08 eV and D0 of 4.19 × 10−4 cm2/sec. These parameters are comparable to those previously reported for impurity ion diffusion. The activation energy obtained is interpreted as that for cation migration. Previous measurements of cation self-diffusion coefficients obtained with the short-lived radisotope 28Mg are an order of magnitude larger and had been interpreted as intrinsic diffusion. The discrepency is attributed to doping introduced by the 28Si decay product of 28Mg.