The phase equilibria of the Sb2Te2S-Bi2Te2S system was studied by powder X-ray diffraction (PXRD), differential thermal analysis (DTA), scanning electron microscope (SEM) and energy dispersive Xray (EDX) microanalysis. It was shown that due to incongruent melting of the Sb2Te2S compound the system is non-quasibinary, but it is stable below the solidus and characterized by the formation of a continuous series of solid solutions with a tetradymite-like hexagonal structure. The lattice parameters were determined from powder diffraction patterns. It was established that the crystal lattice parameters of solid solutions vary linearly with composition

In light of the structural properties of tetradymite-like layered chalcogenide compounds, the mixed-layered compound GeBi3Te4 was predicted and synthesized for the first time, which belongs to the nBi2–mGeBi2Te4 homologous series in the Ge-Te-Bi system. A polycrystal of a new phase was synthesized, and its single crystal was grown by the Bridgman–Stockbarger method. The obtained samples were investigated by differential thermal analysis (DTA) and powder X-ray diffraction (XRD). It was found that the compound melts peritectically at 563 C and has a rhombohedral lattice-type structure with the following lattice parameters: a =4.3625 (5) Å, c = 31.381 (2) Å (sp. gr R3m). The crystal structure of the layered van der Waals compound GeBi3Te4 consists of a repetition of seven-layer GeBi2Te4 packets and two-layer Bi packets in the form of -7-2-7-7-2-7-7-2-7- which differ from the previously discovered GeBi4Te4 phase, which consists of unit cells from only one seven-layer packet. The discovery of a new mixed-layered compound indicates the possibility of the formation of similar compounds in AIV–BV–Te (AIV = Ge, Sn, Pb; BV = Sb, Bi) systems