Phase equilibria of the Sb2Te3+2BiI3↔Bi2Te3+2SbI3 reciprocal system: Synthesis and characterization of the cation-substituted Bi1−xSbxTeI solid solutions

The phase equilibria of the Sb2Te3+2BiI3↔Bi2Te3+2SbI3 reciprocal system have been investigated over the entire concentration range using differential thermal analysis (DTA), powder X-ray diffraction (PXRD), and scanning electron microscopy (SEM) techniques. Liquidus surface projection, solid-phase equilibrium diagram at 300 K and a number of isopleths sections of phase diagram were constructed based on experimental results and literature data. The primary crystallization areas of all the existing phases, their homogeneity ranges, as well as, types and coordinates of non- and monovariant equilibria were revealed. It is determined that the BiTeI−SbTeI section of this reciprocal system is non-quasi-binary due to the incongruent melting of one of the initial ternary compound. However, it is stable at subsolidus and forms wide areas of solid solutions based on the initial compounds. Additionally, dielectric functions and Raman spectra of Bi1−xSbxTeI (x=0; 0.05 and 0.1) phases were studied. The nature of the dependence of the dielectric function on the photon energy was identified based on the obtained ellipsometric data, while Raman spectra show that no structural changes were observed with an increasing concentration of antimony in the solid solution.