Atomic structure and adhesion of the Nb(001)/α-Nb5Si3(001) interface: a first-principles study.

The density functional calculations have been performed to study the Nb(001) and α-Nb5Si3(001) surfaces as well as the interface properties of Nb(001)/α-Nb5Si3(001). The surface energy of the Nb(001) surface is about 2.25 J m (- 2). The calculated cleavage energies of bulk Nb5Si3 are 5.103 J m (- 2) and 5.787 J m (- 2) along (001) planes with the breaking of Nb-Si and Nb-NbSi bonds, respectively. For the Nb(001)/α-Nb5Si3(001) models, the Nb atoms in the interface region initially belonging to body centered cubic metal Nb are twisted to the position of the Nb atom layer in Nb5Si3 and the interlayer distance is similar to that of bulk Nb5Si3 after being fully relaxed. The ideal work of adhesion of the Nb(001)/Nb5Si3(001) interface is calculated and compared to those of bulk Nb and Nb5Si3. The results show that the bulk Nb5Si3 has the largest work of adhesion, the bcc Nb ranks second and the interface ranks last. Moreover, the Nb-Si bond is weaker than Nb-NbSi and Nb-Nb bonds in the interface, which means that the Nb-Si bond in the interface is the most possible site for the micro-crack generation when the stress is applied quasi-statically along the [001] direction. The densities of states, Mulliken population and overlap population of the Nb(001)/α-Nb5Si3(001) interface are also analyzed.