Thermochemistry of the Cu2Se–In2Se3 system

• Solid state EMF experiments were employed to obtain Gibbs energy data of CuInSe2.
• The phase diagram data in the Cu2Se–In2Se3 pseudo-binary system were assessed.
• ΔGf∘ CuInSe2 (α) ± 0.0003 = 0.0051T (K) − 220.92 kJ/mol (949–1044 K) was obtained.
• ΔGf∘ CuInSe2 (δ) ± 0.0004 = −0.0043T (K) − 210.92 kJ/mol (1055–1150 K) was obtained.
• Ttrans and, ΔHtrans∘ for α to δ-CuInSe2 were determined to be 1064 K and 10.0 kJ/mol.

Solid state electrochemical cells were employed to obtain standard Gibbs energy of formation of CuInSe2 as well as the temperature and enthalpy of the α to δ-CuInSe2 transformation in the Cu2Se–In2Se3 pseudo-binary system. The reversible EMF data of the following solid-state electrochemical cell were measured:Pt,In(l),In2O3(s)‖YSZ‖In2O3(s),Cu2Se(s),Cu(s),CuInSe2(αorδ),C,PtCell IThe calculated standard molar Gibbs energy of formation of α and δ-CuInSe2 from measured data are given byΔGf∘CuInSe2(α)±0.0003=0.0051T(K)-220.92kJ/mol(949–1044K)ΔGf∘CuInSe2(δ)±0.0004=-0.0043T(K)-210.92kJ/mol(1055–1150K)The α to δ phase transition temperature Ttrans and the enthalpy of transition ΔHtrans∘ for CuInSe2 were determined to be 1064 K and 10.0 kJ/mol respectively. ΔStrans∘ was calculated as 9.4 J/mol K.The thermodynamic and phase diagram data in the Cu2Se–In2Se3 pseudo-binary system were critically assessed. A self consistent set of thermochemistry and phase diagram data was obtained with the help of measured data. The liquid phase along the Cu2Se–In2Se3 pseudo-binary was calculated with the Redlich–Kister model. The β-Cu1In3Se5 and γ-Cu1In5Se8 phases were represented by the sub-regular model. The ordered non-stoichiometric α-CuInSe2 and δ-CuInSe2 phases were modeled by using a three-sublattice formalism. The calculated phase diagram and thermochemical data show reasonable agreement.