Phase equilibria of the GeTe-Bi2Te3 quasi-binary system in the range 0-50 mol% Bi2Te3

The GeTe-GeBi2Te4 part of the GeTe-Bi2Te3 quasi-binary system was re-examined in the 700-1000 K temperature interval by using PXRD, DTA, and SEM techniques, and the corresponding fragment of the phase diagram was constructed. The existence of 4 ternary compounds is confirmed in the system. Ge2Bi2Te5 (863 K) and GeBi2Te4 (854 K) compounds formed by peritectic reactions, while Ge3Bi2Te6 and Ge4Bi2Te7 decompose by solid-phase reactions. The system is also characterized by the formation of large areas of solid solutions based on both modifications of GeTe. Besides, rhombohedral -> cubic morphotropic phase transition occurs between 9 and 10 mol% Bi2Te3 compositions. The homogeneity field of the cubic phase does not exceed 2-3 mol% at 700 K and layered phases are formed as the concentration of Bi2Te3 increases. Crystallographic parameters of ternary compounds, as well as solid solutions, were determined by the Rietveld method. A comparative analysis of obtained results with literature data is performed.