The central portions of the Cu–Fe–Se phase system at temperatures from 900 to 300 °C

The central portions of the condensed phase system Cu–Fe–Se were investigated by means of dry syntheses in evacuated silica glass tubes at 900, 750, 600, 500, 450, 350, and 300 °C. Synthesis products were studied by reflected-light microscopy and electron microprobe analyses. The field of sulfide melt is extensive at 900 °C and retreats progressively towards the Cu–Se side at 750 °C; residual selenide melt persists at 600 °C. The selenium analogue of iss was found only at and below 600 °C; eskebornite becomes individualized at and below 500 °C, whereas the selenium analogue of bornite solid solution is present at all investigated temperatures, although with reduced extent on temperature decrease. The three iron selenides (β, γ, δ) display considerable solubility of copper, which for the mackinawite-like β FeSe reaches 14 at.% Cu at 300 °C. FeSe2 displays an immiscibility gap with isotropic solid solution (Cu,Fe)Se2, the composition of which gradually changes towards Cu-rich with decreasing temperature. Similarities and differences with the sulfur-based system are highlighted.