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

Abstract First-principles calculations were carried out for the Nb 3 Si, αNb 5 Si 3 , βNb 5 Si 3 and NbSi 2 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 Nb 3 Si → Nb + αNb 5 Si 3 , the transition temperatures of βNb 5 Si 3 to αNb 5 Si 3 , and the range of stability of the NbSi 2 . 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 (βNb 5 Si 3 and Nb 3 Si) should be more ductile (with Nb 3 Si being the most ductile) than the αNb 5 Si 3 and NbSi 2 (with the latter being the most brittle).