The reversible cubic ↔ rhombohedral (O h5 ↔ C 5V3) phase transition of GeTe‐rich (GeTe)1–x[(Ag2Te)0.5333(Bi2Te3)0.4667]xsolid solutions is studied by means of high temperature X‐ray analysis. Temperature and composition changes of the rhombohedral lattice parameters are found. They prove the displacive nature of the solid solution phase transition. With increasing amount of heterovalent Ag and Bi atoms replacing Ge cations the phase transition temperature Tc decreases.
The lattice parameters (a, αR), the change and formation of defects in (GeTe)1−x[(Ag2Te)1−y · (Bi2Te3)y]x solid solutions (SS) vs. the amount of introduced Ag and Bi atoms, and vacancies in cation sublattice at 300 K are studied. X‐ray powder patterns results and also pycnometric density measurements are used. The SS structure changes from rhombohedral to cubic with increasing the number of introduced Ag and Bi atoms, are determined by the parameter \documentclass{article}\pagestyle{empty}\begin{document}$ Z = \frac{{x\left({1 + 2y} \right)}}{{1 + 2xy}} $\end{document}. At equal Z the structure is near to cubic at the greatest amount of Bi atoms (greatest y). The deviation from stoichiometry arising from the SS formula leads to the formation of additional vacancies (+ VN) at y > 0.5 or “excess” cations (− VN) at y < 0.5, the amount of which changes linearly with composition (Z).
The reversible cubicrhombohedral (0: bC:,) phase transition of GeTe-rich ),-,[(Ag,Te),,,s,,,(Bi2Te~)"raai]i solid solutions is studied by means of high-temperature x-ray analysis. The temperature and composition changes of the rhombohedral lattice parameten are found. They prove the displacive nature of the solid solution phase transition. Withan increasingamount ofheterovalent Agand Bi atoms replacingGecations, the phase transition temperature T, decreases.
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Equilibrium polycrystalline samples of GeTe‐rich (GeTe)1−x[(Ag2Te)1‐y(Bi2Te3)y]x (y = 0.4667, 0.5000, and 0.5333) SS are prepared. On the base of different experimental investigations the T‐x projection of the phase equilibrium diagram of SS with y = 0.4667 is drawn. The GeTe‐rich SS keep the crystal structure of GeTe. The phase transition temperature Tc decreases with increasing amount of the ternary compound and reaches 300 K at x of about 0.23. From a comparision of the power coefficient S2σ of SS with different y at 300 K it is found that a deviation in stoichiometry of the ternary compound towards Ag2Te (y = 0.4667) or Bi2Te3 (y = 0.5333) influences unfavorably the thermoelectric parame‐ters.
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