Phase diagrams of the thermoelectric Bi–Sb–Se system

Abstract

Bi–Sb–Se is an important thermoelectric material system. However, a phase diagram of the entire compositional range is not available in the literature. This study determines the Bi–Sb–Se liquidus projection and its phase equilibria isothermal section at 400 °C. Ternary Bi–Sb–Se alloys are prepared. Their primary solidification phases and invariant reactions are determined. There are seven primary solidification phases, (Se), Bi2Se3, Sb2Se3, (Bi,Sb), (Bi2)m(Bi2Se3)n, Bi3Sb5Se2 and Bi3Sb12Se5. Both Bi3Sb5Se2 and Bi3Sb12Se5 are newly found ternary compounds. In the Bi–Sb–Se isothermal section at 400 °C, there are eight three-phase regions. Besides these two ternary compounds, the other single phases are, Sb2Se3, Bi2Se3, (Bi2)m(Bi2Se3)n, Liquid (Bi,Sb), Liquid (Se), and (Bi,Sb) phases. It has been found the solubilities of Sb in the (Bi2)m(Bi2Se3)n and Bi2Se3 compounds are significant.