PHASE EQUILIBRIUM IN THE Cu2Se – SnSe2 – As2Se3 QUASITERNARY SYSTEM

Abstract

77 alloys have been synthesized to study the interaction of the components in the Cu 2 Se –SnSe 2 – As 2 Se 3 quasi-ternary system. The synthesis was carried out by direct single-temperature method from high purity substances (Cu – 99.99 wt.%, Sn – 99.99 wt.%, Se – 99.9997 wt.%, As – 99.9999 wt.%) in evacuated and sealed quartz ampoules. The maximum temperature of the synthesis was 1170 K, homogenizing annealing was carried out at 510 K during 600 h. The obtained samples were investigated by X-ray analysis and differential thermal analysis. The isothermal section of the system at 510 K has been constructed based on the results of the X-ray analysis. The quasi-binary equilibria Cu 2 SnSe 3 – CuAsSe 2 ; Cu 2 GeSe 3 – As 2 Se 3 divide the quasi-ternary system into 3 subsystems: Cu 2 Se – Cu 2 SnSe 3 – CuAsSe 2 ; CuAsSe 2 – Cu 2 SnSe 3 – As 2 Se 3 and Cu 2 SnSe 3 – SnSe 2 – As 2 Se 3 . Solid solutions with large length are not formed, solubilities based on binary, ternary compounds are not more than 5 mol. %. The liquid surface projection of the Cu 2 Se – SnSe 2 – As 2 Se 3 quasi-ternary system has been built based on the literary and obtained results of investigations of the four polythermal sections and one phase diagram. The projection consists of the fields of primary crystallization of Cu 2 Se, Cu 2 SnSe 3 , SnSe 2 , As 2 Se 3 , CuAsSe 2 . They are separated by 8 monovariant curves and 9 nonvariant points. The Cu 2 SnSe 3 – As 2 Se 3 section is quasi-binary and it devides the investigated system into two subsystems: Cu 2 Se – Cu 2 SnSe 3 – As 2 Se 3 (I) and Cu 2 SnSe 3 – As 2 Se 3 – SnSe 2 (II). In the subsystem (I) two nonvariant processes take place:L U1 + Cu 2 Se ↔ Cu 2 SnSe 3 + CuAsSe 2 (peritectic) at 700 K and L E1 ↔ As 2 Se 3 + CuAsSe 2 + Cu 2 SnSe 3 (eutectic) at 600 К. In the subsystem (II) one nonvariant eutectic process L E2 ↔ As 2 Se 3 + Cu 2 SnSe 3 + SnSe 2 takes place at 610 К.