Ab Initio Study of Electronic and Geometric Structures of Metal/Ceramic Heterophase Boundaries

Abstract

ABSTRACTThe adhesion geometries of coherent cube-on-cube interfaces between spinel (MgAl2O4) and the two metals Al and Ag were determined by density functional band structure calculations in the local density approximation (LDA). For Al/MgAl2O4, for which experimental data are available, the calculated optimum interface geometry is in excellent agreement with HRTEM measurements (distance dint: 1.90 Å calc., 1.90±0.04 Å exp.).The work of adhesion Wad is calculated for three different high-symmetry translation states between an Al-0 terminated (001) surface of the spinel and the (001) surface of each of the metals. The binding energy curves display a distinct optimum for the adhesion of aluminum atoms on top of the spinel oxygen ions at a Wad value of 2.4 J/m2. For silver several adsorption sites are isoenergetic at 1.1 J/m2 and the intersections of the Wad (dint) curves indicate a low-energy dissociation path. A further analysis of the electronic structure in the Al/MgAl2O4 system reveals the charge redistribution in the metal towards the oxygen ions as the main contribution to bonding. On the contrary, polarization of the metal film is the major effect observed on the adhesion of Ag to the spinel substrate.