New aspects of the system CuAsS

Abstract

The system CuAsS was investigated by differential thermal analysis and X-ray methods. The quasibinary sections Cu 2S-As, As-Cu 3AsS 3, Cu 3AsS-Cu 2S and Cu 2S-As 2S 3 were found. The last of these contains most of the ternary compounds. The previously reported CuAsS 2 was not observed. Two closely related compounds “Cu 6As 4S 9” (sinnerite) and “Cu 4As 2S 5” (monoclinic: a = 1035.0 pm; b = 1465.0 pm; c = 3334.0 pm; β = 96°) decompose peritectically. These two compounds and Cu 24As 12S 31, reported by Maske and Skinner, are substructures of the sphalerite structure and parts of the broad homogeneity region of “Cu 4As 2S 5” in the ternary system. Two modifications of the congruently melting compound Cu 3AsS 3 were observed. The low temperature modification is known as the mineral tennantite. The high temperature modification could be obtained at ambient temperature by quenching. Some observations indicate that a compound Cu 5AsS 4 similar to the mineral stephanite (Ag 5SbS 4) might exist.