A refined phase diagram of the GeTe-Bi2Te3 system

Abstract

Updated phase diagram of the GeTe–Bi2Te3 system was constructed using differential thermal, X-ray diffraction analysis and scanning electron microscopy (SEM) results of alloys synthesized with specially developed technology. The refined version significantly differs from those reported so far. The presented phase diagram reflects six ternary compounds: Ge4Bi2Te7, Ge3Bi2Te6, Ge2Bi2Te5, GeBi2Te4, GeBi4Te7, and GeBi6Te10. The study determined that the first two compounds are formed as a result of solid-state reactions at temperatures of 750–800 K, and the latter four are formed as a result of peritectic reactions at 863, 854, 848, and 843 K, respectively. Wide homogeneity regions based on the initial binary compounds were also found. These regions reach 10 mol% at room temperature. The coordinates of eutectic point are 83 mol% Bi2Te3 and 838 K. It crystallises at 838 К. It was found that all the identified ternary compounds crystallise in a tetradymite-like layered structure. Ge4Bi2Te7, Ge3Bi2Te6, Ge2Bi2Te5, and GeBi2Te4 compounds belong to the nGeTe·Bi2Te3 homologous series. Their crystal lattices are formed by the insertion of GeTe bilayers into the quintuple Bi2Te3 layers. GeBi4Te7 and GeBi6Te10 compounds are representatives of the GeTe·mBi2Te3 homologous series and have a mixed-layer structure. The parameters of the crystal lattices of the compounds were determined by the Rietveld method based on their powder diffraction data.

Keywords

• germanium-bismuth tellurides
• phase diagram
• layered tetradymite-like structures
• solid solutions