Some aspects on thermodynamic properties, phase diagram and alloy formation in the ternary system BAs–GaAs—Part I: Analysis of BAs thermodynamic properties

Abstract

Owing to the lack of available thermodynamic data based on experimental measurements of heat capacity, decomposition reaction or vapour pressure measurements, the problem of BAs stability is considered. We propose a new set of thermodynamic data for enthalpy of formation, entropy and Gibbs free energy of Bas compound. By using thermodynamic database, our approach is based on the semi-empirical trends and analogy in the variation of those quantities for several binary series in different III–V systems like arsenides, nitrides and phosphides. Thus, the values for BAs were derived by extrapolation from Al to boron-based compounds (BAs, BP and, BN). For pure BAs(s), we predict a low enthalpy of formation in the standard state of Δ f H 0 ( BAs ) ≈ - 30 kJ / mol at 300 K and a Gibbs free energy of Δ f G 0 ( BAs ) ≈ - 40 ± 5 kJ / mol indicating a lower stability of this compound than GaAs. Those values are contradictory discussed with trends in the cohesive energy of several III–V systems. A cohesive energy of ∼900 kJ/mol (9.4 eV) is proposed in agreement with Philips's rule.