Isomorphism and solid solutions among Ag- and Au-selenides

Au-Ag selenides were synthesized by heating stoichiometric mixtures of elementary substances of initial compositions Ag_2-xAu_xSe with a step of x=0.25 (0≤x≤2) to 1050 °C 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 Ag₂Se - Ag_1.94Au_0.06Se, fischesserite Ag₃AuSe₂ - Ag_3.2Au_0.8Se₂ and gold selenide AuSe - Au_0.94Ag_0.06Se. 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.