HRTEM study of a Cu/Al2O3interface

The interface between Cu and faceted particles of a cubic Al2O3 phase in an internally oxidized CuAl alloy was studied by HRTEM. Image simulations indicate that the Al2O3 precipitates have a highly disordered spinel-type structure. The precipitates grow by ledge migration and possess internal defects, mainly coherent twin boundaries and stacking faults. At the Cu/Al2O3 interface, two orientation relationships were observed: ‘parallel topotaxy’ and ‘twin topotaxy’. The interface was always parallel to {111} planes of the Al2O3. No localized misfit dislocations were observed either by HRTEM or by weak beam dark field electron microscopy. The atomistic configuration at the interface is well described by a rigid lattice model assuming that a partially occupied oxygen layer terminates the Al2O3.