DESCRIPTION OF THE TERNARY-SYSTEM AG-AS-TE

The phase diagram of the Ag-As-Te system was studied by means of differential thermal analysis, X-ray diffraction, and metallographic analysis. Two ternary phases were observed: Ag11AsTe7 and AgAs3Te5, both showing a peritectic decomposition of the binary type at 405 and 331-degrees-C, respectively. The Ag11AsTe7 phase, whose structure we have not vet solved, exhibits a hexagonal cell and is isotypic of Ag11.67Te7 (Ag5Te3). This phase was merely observed in a narrow temperature range (145-405-degrees-C). The existence of a continuous solid solution between Ag11.67Te7 and Ag11AsTe7, accompanied with the consequent appearance of two two-phase domains, was claimed according to triangulation and numbering of the ternary invariants. Due to the fact that the parameters of the two phases were very close, it was not possible to confirm the existence of this solid solution by measuring parameters variation as a function of composition. The lattice of the AgAs3Te5 phase still remains unknown. Moreover, we were not able to synthetize a AgAsTe2 phase. Two quasi-binary sections are described in this system. Eight ternary invariants, among which three are almost completely merged into the binary invariants of the Ag2Te-As2Te3 system, where characterized: three eutectics and five peritectics. Their localization was set up as a function of temperature and composition. A ternary liquid-liquid miscibility gap was observed from the binary monotectic invariant in the Ag-Te system. Finally, a very extended glass domain was found near As2Te3, which is rather unusual in telluride systems. (C) 1994 Academic Press, Inc.