Ab-initio study of the local bonding at metal-ceramic heterophase boundaries

The adhesion geometries of the (100) heterophase boundaries between the metals Al or Ag. and spinel (MgAl2O4) were determined by density-functional calculations employing a mixed-basis pseudopotential method. The results compare well with high-resolution transmission-electronmicroscopy studies which were carried out in parallel. An analysis of the calculated electronic structures shows that the strong adhesion of Al on spinel is mediated by directional bonding. The comparatively weak interaction of spinel with Ag is dominated by polarization effects which can be classified as originating from an image-charge interaction. Additionally, the effects of changes in stoichiometry and of segregated substitutional atoms at the interface were analyzed in terms of the excess of the corresponding component at the interface. The implications for the geometric structure and the related mechanical properties at the metal-ceramic junctions are discussed.