Experimental investigation of the solid phase equilibria at 300 K in the SnBi2Te4-PbBi2Te4-Bi2Te3 system

The phase equilibria of the SnBi2Te4-PbBi2Te4-Bi2Te3 system were experimentally studied using differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM) techniques. According to the experimental results, the isothermal section of the system at 300 K were constructed and 4 single-phase and 3 two-phase regions were identified. It was shown that along with previously confirmed SnBi2Te4–PbBi2Te4 and SnBi4Te7–PbBi4Te7 sections, SnBi6Te10–PbBi6Te10 section forms continuous series of solid solutions with a tetradymite-type layered structure. Lattice parameters of solid solutions were determined by full-profile Rietveld refinements and results show that both a and c parameters increase linearly with the Pb concentration according to Vegard's law. This study can help elucidate the phase equilibria of the SnTe-PbTe-Bi2Te3 pseudo-ternary system which provides important information for the design of new tetradymite-type layered phases with topological insulator and thermoelectric properties.