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 TaSn₂were 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.