Diffusion of Iron and Nickel in Magnesium Oxide Single Crystals

Abstract

Diffusion kinetics and mechanisms were studied in the Fe x O‐MgO (vacuum), NiO‐MgO (vacuum and air), and Fe 2 0 3 ‐MgO (air) systems. In the Fe x O‐MgO system, Fe entered MgO by a redox reaction; the diffusivity and activation energy depended on concentration. In the NiO‐MgO system in air the diffusivity depended on concentration and the activation energy did not; in vacuum both the diffusivity and activation energy were concentration‐independent. In the Fe 2 O 3 ‐MgO system in the MgO phase the activation energy and diffusivity did not depend on concentration. Because of impurities, the diffusion results were for the extrinsic region. Formation of trivalent ions and consequent chemically created vacancies in the Fe x O‐MgO and NiO‐MgO (air) systems resulted in the concentration dependence of diffusivity. Concentration dependence of activation energy in the Fe x O‐MgO system is associated with structural changes due to a change with concentration of the Fe 3+ octahedraI/Fe 3+ tetrahedral ratio. In the Fe 2 O 3 ‐MgO system structural changes do not occur during diffusion because this ratio remains constant.