Isomorphism and solid solutions among Ag- and Au-selenides

Abstract Au-Ag selenides were synthesized by heating stoichiometric mixtures of elementary substances of initial compositions Ag 2−x Au x Se with a step of х=0.25 (0≤х≤2) to 1050 °С and annealing at 500 °C. Scanning electron microscopy, optical microscopy, electron microprobe analysis and X-ray powder diffraction methods have been applied to study synthesized samples. Results of studies of synthesized products revealed the existence of three solid solutions with limited isomorphism Ag↔Au: naumannite Ag 2 Se – Ag 1.94 Au 0.06 Se, fischesserite Ag 3 AuSe 2 - Ag 3.2 Au 0.8 Se 2 and gold selenide AuSe - Au 0.94 Ag 0.06 Se. Solid solutions and AgAuSe phases were added to the phase diagram of Ag-Au-Se system. Crystal-chemical interpretation of Ag-Au isomorphism in selenides was made on the basis of structural features of fischesserite, naumannite, and AuSe.