A DENSITY-FUNCTIONAL STUDY OF INTERACTIONS AT THE METAL-CERAMIC INTERFACES AL MGAL2O4 AND AG/MGAL2O4/

'Ab-initio density-functional calculations were performed on the geome tric and the electronic structures of coherent cube-on-cube interfaces between spinel (MgAl2O4) and the two metal Al and Ag. The calculation s were carried out in the local density approximation (LDA) employing norm-conserving pseudopotentials and a mixed basis set of plane waves and local orbitals. The cohesive properties of the bulk materials are determined in good agreement with experiment. Four different high-symm etry translation states between the metal atoms and an Al-O or a Mg te rmination layer of the spinel are investigated at the unrelaxed interf ace distance. For Al a marked preference for the on-top O posit-on on the Al-O layer is found, whereas for Ag the follow-site positions are slightly preferred over the on-top O position on the Al-O layer. An op timization of the interface distance yields a distinct energy minimum at 1.90 Angstrom for Al/MgAl2O4 on the on-top O site, in very good agr eement with experiment. For Ag the total-energy curves of the differen t adhesion sites intersect and enable a low-energy dissociation path.