REINVESTIGATION OF THE GeTe-Sb2Te3 PSEUDOBINARY PHASE DIAGRAM

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