Stability of the D8_m-Ti₅Sn₂Ga compound. Experimental determinations and first principle calculations

Highlights: • Experimental study of phase relationships was obtained at high temperature in the Ti₅Sn₃ region. • The formation energy of the D8_m-Ti₅Sn₂Ga compound is obtained by using DFT calculations. • The D8_m-Ti₅Sn₂Ga compound is stable and possesses a domain of off-stoichiometry. - Abstract: In this paper we discuss the formation of the ternary compound Ti₅Sn₂Ga (τ) with the D8_m structure. Phase equilibria with participation of the τ-phase were studied experimentally, and partial solidus projection and isothermal section at 1300 °C were plotted. At the solidus temperatures the ternary compound is in equilibria with two continuous solid solutions: (1) between Ti₂Sn and Ti₂Ga (named Ti₂(Sn, Ga)) and (2) between Ti₅Sn₃ and Ti₅Ga₄ (named Ti₅(Sn, Ga)_3–4). At 1300 °C Ti₂Sn and Ti₂Ga do not form continuous solid solution, and the ternary compound participates in equilibria with Ti₅(Sn, Ga)_3–4, and Ti₂Sn, Ti₂Ga and Ti₃Sn based phases. The formation energy of the D8_m-Ti₅Sn₂Ga compound is calculated by using electronic density-functional theory (DFT) using pseudopotentials constructed by the projector augmented waves (PAW) method in the generalized gradient (GGA) approximation for the exchange and correlation energy. The calculated lattice parameters are in good agreement with the experimental values. According to the experiments and the ab initio calculations, the D8_m-Ti₅Sn₂Ga compound is stable and possesses a domain of off-stoichiometry