Thermochemistry of the Ga-Se System

Abstract

Solid state electrochemical cells were employed to obtain standard Gibbs energy of formation of Ga2Se3 as well as the temperature and enthalpy of the α to β-Ga2Se3 transformation in the Ga-Se system. The reversible Emfs of the following solid-state electrochemical cells were measured: Pt, Ga(l), Ga2O3(s)||YSZ||Ga2O3(s), GaSe(s), Liquid1, C, Pt I; Pt, Ga(l), Ga2O3(s)‖YSZ‖Ga2O3(s), GaSe(s), Ga2Se3(s), C, Pt II; Pt, Ga(l), Ga2O3(s)||YSZ||Ga2O3(s), Ga2Se3(s), Liquid2, C, Pt III. The standard molar Gibbs energy of formation of Ga2Se3, which was calculated by analysis of measured data, is given by: ΔGof(Ga2Se3, α) ± 1.00(kJ/mol) = −442.65 + 0.11816 T(K) (823 − 962 K); ΔGof(Ga2Se3, β) ± 0.48(kJ/mol) = −425.46 + 0.10086 T(K (986 − 1100 K). The thermodynamic and phase diagram data in the Ga-Se system were critically assessed. A self consistent set of thermochemistry and phase diagram data was obtained with the help of thermochemical measurements. The liquid phase was modeled by the associated solution model with two associates of GaSe and Ga2Se3. The α-Ga2Se3 phase was described by the sublattice model with two sublattices according to the formula (Ga,Va)2 (Se,Va)3. The other two intermediate phases, GaSe and β-Ga2Se3 were treated as line compounds.