Ab-initio study of the stability of the D8m-Nb5Sn2Ga and D8m-Ta5SnGa2 compounds
Résumé
First principles calculations have been performed in the T-Sn-Ga (T = V, Nb, Ta) systems along the section x(T) = 0.625. The enthalpies of formation of the binary and ternary D8(m), D8(1), and D8(8) structures have been calculated. In the V-Sn-Ga system, no ternary structure is stable in the section. In the Nb-Sn-Ga system, the ternary compound D8(m)-Nb5Sn2Ga is stable. In the Ta-Sn-Ga system, a combination of the ab-initio calculations and Gibbs energy calculations using the sublattice model allows the show that the phase D8(m)-Ta-5(Sn,Ga)(2)Ga with a mixed occupancy of the 8h sites of the structure by Ga and Sn atoms is stable at high temperature due to the configurational entropy. These results are in agreement with the experimental determinations previously published in the literature.