THE SnAs–P POLYTHERMIC SECTION OF Sn–As–P TERNARY SYSTEM

Abstract

Objective. In recent years, tin phosphides and arsenides have been actively studied as very promising materials for the manufacture of anodes of Li (Na, K)-ionic batteries. The formation of solid solutions based on these compounds with the mutual replacement of phosphorus and arsenic atoms takes place quite easily. The use of solid solutions instead of pure compounds allows one to expand the range of useful properties of the material. This determines the relevance of the study of phase relationships in the Sn–As–P ternary system. The purpose of this paper is to study the SnAs–P polythermal cross section by the methods of X-ray phase analysis (XRD) and differential thermal analysis (DTA). Methods and Methodology. The samples were obtained in the concentration range of 0.05-0.60 mol.f. phosphorus by fusing simple substances of tin, arsenic and red phosphorus in evacuated quartz ampoules. Then the alloys were annealed at a temperature T = 773 K for 150 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. Thermoanalytical studies were carried out using Stepanov’s quartz vessels. X-ray powder diffraction (XRD) analysis of samples of the SnAs–P section were performed using a powder diffractometer ARL X’TRA with the following characteristics: CuKa-radiation, exposure step 0.06o, exposure time 3.0 seconds. Results. X-ray phase analysis showed that all the alloys represent the mixture of three phases: solid solution based on SnAs (b), solid solution based on SnP3 (g) and solid solution of tin in the intermediate phase As1–хPх (d). The extent of the b-solid solution along the SnAs–Р section is less than 0.05 mol.f. On thermograms of samples with phosphorus concentration 0.20-0.60 mol. f. the same temperature of onset of the fi rst endothermic effect was observed (827±2 K). Conclusions. Based on the DTA data, taking into account the XRD-results and the theoretical analysis of phase equilibria in the Sn–As–P system, T-x diagram of the SnAs–Р polythermal section was constructed. The presence of a horizontal line at a T-x diagram at a temperature of 827 ± 2 K corresponds to the the existence of the invariant peritectic equilibrium L+ (d) ↔ b + g in the Sn–As–P system.

Keywords

• Sn–As–P system
• phase equilibria
• solid solutions