Phase equilibria in the PbSe-Bi2Se3-Se system and thermodynamic properties of intermediate phases

Abstract

The Pb-Bi-Se system in the PbSe-Bi2Se3-Se-Se composition region was studied by measurement of concentration circuits of the type (−) PbSe(solid) liquid electrolyte, Pb2+(Pb-Bi-Se)(solid) (+) in the temperature range 300–430 K and by X-ray powder diffraction. A solid-phase equilibrium diagram was constructed, and the formation was confirmed for the ternary compounds Pb5Bi6Se14, Pb5Bi12Se23, and Pb5Bi18Se32, which belong to the homologous series [(PbSe)5]m · [(Bi2Se3)3]n. From the emf versus temperature equations, the partial thermodynamic functions \(\overline {\Delta G}\), \(\overline {\Delta H}\), \(\overline {\Delta S}\) of PbSe in alloys were calculated. Based on the solid-phase equilibrium diagram from these partial molar quantities using the corresponding data for PbSe and Bi2Se3, the standard thermodynamic functions of formation and standard entropies of the above ternary compounds were calculated.