The effect of Me-Ti inter-atomic interactions on wetting in CaF₂/(Me-Ti) systems: Ab-initio considerations

CaF₂ is a thermodynamically stable, non-reactive compound, displaying a relatively high contact angle with pure liquid metals. A remarkable decrease of this contact angle takes place when small amounts of Ti are added to liquid In, while a relatively small change of the contact angle is observed when it was added to liquid Sn. In order to understand the reason for this different behavior, ab-initio calculations were carried out in the framework of Density Functional Theory. The effect of the In-Ti and Sn-Ti inter-atomic interactions in the vicinity of CaF₂(1 1 1) slab is discussed using the results of modest calculations for several Me-Ti configurations on CaF₂(1 1 1) slabs. The results of the calculations indicate that the level of the interaction between the Me and the Ti atom affects the (Me-Ti)/CaF₂ interface composition, the interfacial energy and the wetting behavior. For the system with stronger inter-atomic attraction in the melt (Sn-Ti alloys), Ti atoms prefer to be surrounded by Sn atoms, and only weakly affect the metal/substrate interfacial energy and, thus the observed contact angle. However, for weak inter-atomic attraction (In-Ti alloys) an enhanced Ti adsorption at the metal/substrate interface takes place and leads to decrease the interfacial energy and improved wetting. The differences in the wetting behavior for these systems are discussed in terms of the total energy of each system, the electron charge re-distribution and the electron Density of States.