First-principles calculations and thermodynamic modeling of the Sn-Ta system

A thermodynamic description of the Sn-Ta system was developed using the CALPHAD (CALculation of PHAse Diagram) approach in combination with first-principles calculations. A positive enthalpy of mixing of the body centered cubic phase was predicted, using special quasirandom structures (SQS), indicating the tendency to form a miscibility gap. The finite temperature thermodynamic properties of Ta3Sn and TaSn2 were calculated by the Debye-Grüneisen model as well as phonon calculations using the supercell approach. The results from first-principles calculations along with the previously reported decomposition temperature of TaSn2, 868 °K, were used to evaluate the Gibbs energy parameters of the TaSn2, Ta3Sn intermetallics and the liquid phase. No decomposition temperature of Ta3Sn has previously been reported in the literature but was predicted in this work to be 2884 °K. The calculated phase diagram agrees well with available experimental information of the Sn-Ta system and also compares well with similar systems such as Nb-Sn and V-Sn.