Phase relations in the Cu-Te-S system at temperatures between 350 and 900 degree C

Phase relations were determined in the Cu-Te-S system at 350, 450, 550, 675, 800 and 900 degree C. At 350 degree C three ternary phases are present, goldfieldite and two phases A and B, which have not been found i nature. Phase A has disappeared by 450 degree C, goldfieldite has disappeared by 550 degree C, and phase B has disappeared by 800 degree C.

Godlfieldite and phase A (Cu5Te4S8) have no detectable compositional ranges. Goldfieldidte has a cubic, face centered cell with a=10.242(22) Å. Phase A is monoclinic primitive, a = 6.51 Å, b = 3.72 Å, c = 18.11 Å, beta = 80.84 degree and Z = 1. Phase B has a long and narrow compositional field at all temperature levels with nearly constant Cu content and an ideal formula based on 16 atoms is Cu10(Te6-xSx) with 0.4>x>3.3 and Z = 10.

The phase is cubic body centeret with a ranging from 14.337(103) Å (S-poor) to 14.827(69) Å (S-rich). X-ray powder data and optical data on phases A and B are listed. At 350 degree C there exist two liquid fields which at 450 degree C have become one continuous field stretching from Cu45Te55 with low S content to the tellurium corner of the phase diagram and from there to the sulphur corner.

With increasing S, the Cu content of the liquid rapidly decreases to trace amonts. With increasing temperature the field extends into the ternary from the tellurium corner towards the Cu-S join. The boundary of the liquid field in the central portion of the phae diagram towards the sulphur corner does not change position with an increase in temperature from 550 to 900 degree C.