The paper presents the results of a restudy of phase equilibria in the pseudobinary system GeTe–Sb₂Te₃ using differential thermal analysis, powder X-ray diffraction, and scanning electron microscopy. A new version of the phase diagram has been constructed, which reflects six layered tetradymite-type ternary compounds: Ge₄Sb₂Te₇, Ge₃Sb₂Te₆, Ge₂Sb₂Te₅, GeSb₂Te₄, GeSb₄Te₇, and GeSb₆Te₁₀. The first two compounds decompose according to solid-phase reactions, and the others melt with decomposition according to peritectic reactions. The new diagram includes a cascade of invariant peritectic reactions in a narrow temperature range. The lattice parameters of all ternary compounds have been refined using the Le Bail method and the obtained results are in good agreement with the literature data. At a temperature of 700 K, the homogeneity regions based on GeTe and Sb₂Te₃ reach ~12 mol% and ~10 mol%, respectively. It was found that at approximately 10 mol% Sb₂Te₃ in solid solutions, a morphotropic phase transition occurs from the rhombohedral to the cubic structure. At 700 K, the homogeneity regions of the rhombohedral and cubic phases span composition ranges of 0–9 mol% and 9–12 mol% Sb₂Te₃, respectively.

Keywords: germanium antimony tellurides, phase equilibria, layered compounds, phase change materials, topological insulators.

doi.org/10.32737/0005-2531-2025-2-95-103