ELECTRON-MICROSCOPY STUDIES OF METAL MGO INTERFACES

Electron microscopy has been used to study the structure of Cu/MgO and Pd/MgO interfaces formed by internal oxidation of Cu-1wt%Mg and Pd-1wt%Mg alloys. For the Cu/MgO system, the MgO particles exhibit a cube-on-cube orientation relationship with the Cu matrix and are octahedrally shaped with principal facets parallel to {111} lattice planes of MgO and Cu. For the Pd/MgO system, however, both tetradecahedron and plate-like MgO precipitates are observed. The tetradecahedrally shaped particles also exhibit a cube-on-cube orientation relationship with the Pd with principal facets parallel to {111} and {100} lattice planes. The plate-like MgO precipitates have two of their {111} surfaces parallel to the {111} surface of Pd and exhibit a twin orientation relationship with respect to the Pd matrix. All interfaces are partially coherent. The localized misfit dislocations at Pd/MgO{111} and {100} interfaces are visible by weak-beam imaging. For both Cu/MgO and Pd/MgO interfaces, the periodic strain contrast caused by misfit dislocations are seen in HREM micrographs. Image simulations have been performed to confirm the presence of misfit dislocations.