First-Principles Calculations of the Ideal Cleavage Energy of Bulk Niobium(111)/α-Alumina(0001) Interfaces

We report ab initio calculations of the work of adhesion for O- and Al-terminated Nb(111)/ $\alpha$-alumina(0001) interfaces. Strong ionic bonds formed by Nb4 $d$ $\to$ O2 $p$ electron donation account for the high adhesive strength of O-terminated interfaces. However, cleavage preferentially occurs between metal atoms at both O- and Al-terminated interfaces, and their adhesion has both covalent and ionic character.