Density functional study of the 'titanium effect' at metal-ceramic interfaces

A thin interlayer of an early transition metal, e.g. titanium, can enhance the bonding at a metal-ceramic interface considerably. The role of the elec tronic structure in this phenomenon (the 'titanium effect') is studied quan titatively by means of density functional calculations, employing norm-cons erving ab initio pseudopotentials and a mixed basis of localized functions and plane waves. The weakly bonding model interface Ag(100)/MgAl2O4(100) is chosen, in order to minimize the lattice mismatch and to concentrate on el ectronic interactions. The stepwise addition of Ti atoms at the interface f rom zero to one monolayer of Ti leads to a pronounced enhancement of the bo nding strength (Ag/Ti/MgAl2O4), From a comparison to the more strongly bond ing systems Ag/Al/MgAl2O4 with a monatomic Al interlayer and Al/MgAl2O4 it is concluded that this enhancement correlates with the reduction of the ele ctron density in the interface layer. It is proposed that the interlayer ac commodates Pauli repulsion between O anions and electron-rich Ag atoms by s uitable electron redistribution, which is accompanied by pronounced energy band shifts.