Theoretical Investigation of the Thermodynamic Properties of η′-(Cu, Co)₆Sn₅ Alloys

We perform theoretical investigations on the structures of η′-Cu₆Sn₅-based intermetallic compounds (IMCs) with different Co doping concentration (0–12.2 wt.%) based on density functional theory (DFT). The variations of the structural, elastic and thermodynamic properties of (Cu, Co)₆Sn₅ IMCs with pressure (0–18 GPa) and temperature (0–500 K) are obtained with the application of quasi-harmonic Debye model for the non-equilibrium Gibbs free energy. It is found that the volume of (Cu, Co)₆Sn₅ shrinks with Co concentration increasing in the range of imposed pressure and temperature. At the same time, the bulk modulus of Cu₄Co₂Sn₅ is the largest among those of Cu₆Sn₅, Cu₅Co₁Sn₅ and Cu₄Co₂Sn₅. By calculating the Debye temperature of Cu₆Sn₅, we find that it is higher than that of Cu₅Co₁Sn₅ and Cu₄Co₂Sn₅ when the pressure is higher than 2 GPa. Meanwhile, heat capacities of all three Cu₆Sn₅, Cu₅Co₁Sn₅, and Cu₄Co₂Sn₅ converge to a near-constant value at about 1090 J/mol K in the range of the imposed pressures.