Thermodynamic Modeling of the Cu-Sb-Se System

The doping with Cu in the Sb-Se material system can effectively reduce power consumption and improve data retention ability of the PCRAM (Phase-Change Random-Access Memory) material. However, no thermodynamic study of the Cu-Sb-Se system has been reported. Therefore, in this work the Cu-Sb-Se system was modeled using the CALPHAD (CALculation of PHAse Diagrams) method. The excess Gibbs energies of solution phases, including liquid and FCC were expressed by the Redlich-Kister polynomial. Two-sublattice model (Cu,Se)₂Se was used to describe the solid solution of binary intermetallic compounds, i.e. α-Cu₂Se and β-Cu₂Se in Cu-Sb-Se ternary system. The compounds, e.g. η(Cu₂Sb), β(Cu₃Sb), Sb₂Se₃, α-CuSe, β-CuSe, Pe(Cu₃SbSe₄) and C(CuSb₃Se₅) were described as stoichiometric compounds. The temperature of the eutectic reaction γ(Cu₁₇Sb₃) = (Cu) + δ(Cu₄Sb) in the Cu-Sb system and the temperature of the invariant reaction L1 = L2 + (Sb) in the Sb-Se system were adjusted. A set of self-consistent thermodynamic parameters for the Cu-Sb-Se system was obtained, and the 623, 673, 723, 773, 873 and 973 K isothermal sections, and the liquidus projection and invariant reactions for this ternary system have been calculated.