Influence of Iron Solute on the Structure of Small‐Angle [001] Twist Boundaries in Magnesium Oxide

Abstract

The structure of small‐angle [001] twist boundaries in pure and Fe‐doped MgO was examined by electron imaging techniques in order to study the influence of solute on grain‐boundary structure. In addition, the effect of the oxidation state of the Fe on the boundary structure was also examined. The [001] twist boundaries were produced in the form of bicrystals, by the hot‐pressing of cleaved single crystals of pure MgO and MgO containing Fe. In pure MgO the [001] twist boundaries produced with small plastic strains are planar and contain a square array of screw dislocations with Burgers vectors of the type a/2<110>. In the presence of solute the original interface becomes wavy and dissociates into subboundaries. Distorted hexagonal dislocation networks as well as square arrays of screw dislocations are often observed in Fe‐doped MgO. These observations are evidence that [001] twist boundaries in MgO whose production was accompanied by small amounts of plastic deformation undergo a structural transformation induced by the presence of Fe solute. The influence of the Fe oxidation state on boundary structure is less well understood. It appears that when the [001] twist boundaries are produced using crystals containing a substantial amount of Fe3+ ions, the resulting boundary structure is more likely to contain distorted hexagonal dislocation networks than when the boundary is produced from crystals containing predominantly Fe2+ ions.