Determination of Thermodynamic Properties of Si-B Alloys

This study establishes the thermodynamic properties of the Si-B binary alloy system. The electromotive force (emf) as a function of temperature (823 K to 923 K) was measured using solid-state electrochemical cells, represented as$$(-)\text{Pt},\text{Ar}/\{\text{Si}\parallel {\text{CaF}}_2\parallel \{\text{Si}-\text{B}\left(\text{alloy}\right)\}/\text{Ar},\text{Pt}(+)$$ Using the experimental emf data obtained from the solid-state heterogeneous phase equilibrium, the activities of Si and B in Si-B alloys were calculated. The integral Gibbs energy of mixing $\left(\Delta G^{\text{M}}\right)$ of alloys were calculated from the activity of Si and B. A large negative deviation from ideality was found for the integral Gibbs energy of mixing $\left(\Delta G^{\text{M}}\right)$ of the binary Si-B system. From the activities of Si and B, the Gibbs energies of formation $\left(\Delta G_f^0\right)$ of phases present were calculated. The $\Delta G_f^0$ of SiB₃, the most thermodynamically stable phase, was calculated as − 13.13 ± 0.19 kJ/mole-atoms at 923 K. The heterogeneous phases and microstructure after the equilibrium study of the electrode were characterized using XRD, SEM, and EDS analyses.