Ab initio study of the intermetallics in Nb-Si binary system

First-principles calculations were carried out for the Nb3Si, αNb5Si3, βNb5Si3 and NbSi2 intermetallic compounds and their constituent elements. The enthalpies of formation were computed for all the intermetallic compounds, as well as the eutectoid transformation temperature for Nb3Si → Nb + αNb5Si3, the transition temperatures of βNb5Si3 to αNb5Si3, and the range of stability of the NbSi2. There was good agreement between the results of the present study and the Nb-Si phase diagram. The elastic constants, bulk, shear and Young's moduli, Poisson's ratio and Debye temperature were also calculated for the intermetallic compounds and Nb and Si. The Cauchy pressures, Pugh's index and Poisson's ratio indicate that the high temperature phases (βNb5Si3 and Nb3Si) should be more ductile (with Nb3Si being the most ductile) than the αNb5Si3 and NbSi2 (with the latter being the most brittle).