Analysis of phase equilibria in the Ge–P–Sn ternary system

Abstract

Objective. Great attention to compounds with a layered structure because of the possibility of formation of functional 2D materials on their basis predetermined the interest in compounds of the group AIVBV, in particular GeP. However, the high vapor pressure of phosphorus creates the complexity of the synthesis of this phase, so they use a solvent - tin or bismuth, which signifi cantly softens the conditions for obtaining samples. In this case, other phases may form, according to the nature of the equilibria in the ternary systems. This determines the relevance of research on the nature of phase equilibria in Ge – P – Sn ternary system. The purpose of this paper is to analyze the phase diagram of the Ge – P – Sn system and possible equilibrium schemes that take into account the features of binary systems that bounding this ternary system, based on an experimental study of the Sn4P3-Ge and Sn4P3-GeP polythermal cross sections.

Methods and Methodology. The samples were obtained by fusing simple substances of tin, germanium and red phosphorus in evacuated quartz ampoules. Then the alloys were annealed at a temperature 753 К for 120 hours. The study of the samples was carried out on the differential thermal analysis (DTA) setup with a programmable heating of the furnace. In our experiments, the heating rate of DTA-setup was 5 K · min–1. X-ray powder diffraction (XRD) analysis of samples was performed using a powder diffractometer ARL X’TRA with the following characteristics: CuKa-radiation, exposure step 0.06o, exposure time 3.0 seconds.

Results. As follows from the data of differential thermal analysis, the phase diagram of the Sn4P3–GeP section is a diagram of the eutectic type with the coordinates of the eutectic point of 800 K, 15 mol % Ge. An experimental study by the X-ray phase analysis of alloys whose compositions correspond to polythermal section Sn4P3–GeP made it possible to establish the nature of the phase separation of the system at temperatures below the solidus. In the system invariant peritectic equilibrium L + Ge ↔ GeP + Sn₄P₃  takes place, and there are also three triple eutectic points, responding to the processes L ↔ Ge + Sn + Sn₄P₃ ; L ↔ GeP + SnP₃ + Sn₄P₃  and L ↔ P + GeP + SnP₃

Conclusions. Taking into account the nature of phase equilibria in binary systems, two possible schemes of sub-solidus phase separation of the Ge – P – Sn ternary system diagram are proposed. The choice was made on the basis of X-ray phase analysis of samples of polythermal section Sn₄P₃ –GeP. It was established that the sectionґs alloys are a mixture of three phases – Sn₄P₃ , GeP and Ge. Accordingly, the separation of the diagram below the solidus temperature is performed by Sn₄P₃-Ge, Sn₄P₃–GeP and SnP₃–GeP cuts.

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