Ab-initio study of the stability of the D8m-Nb5Sn2Ga and D8m-Ta5SnGa2 compounds

• First principles calculations were performed along sections V5Sn3–V5Ga3, Nb5Sn3–Nb5Ga3, and Ta5Sn3–Ta5Ga3.
• The ternary compound D8m-Nb5Sn2Ga is stable.
• The phase D8m-Ta5SnGa2 is stable in the D8m structure.
• In this phase, the Sn and Ga atoms share the 8h sites.

First principles calculations have been performed in the T–Sn–Ga (T = V, Nb, Ta) systems along the section xT = 0.625. The enthalpies of formation of the binary and ternary D8m, D81, and D88 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 D8m-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 D8m-Ta5(Sn,Ga)2Ga 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.

Thermodynamic data along the sections Ta5Sn3–Ta5Ga3 at low and high temperature.Figure optionsDownload as PowerPoint slide