Synthesis, characterization, stability and structure of solid solutions between ?-miargyrite(AgSbS2) – smithite (AgAsS2) and ?- miargyrite - smithite

Sulphosalts in the system AgSbS2-AgAsS2 have been experimentally investigated using dry methods. The solid solutions which form between ?-miargyrite and smithite have different structures. The EPMA data for the solid solution series show that there is an inverse relation between Sb and As. The cell parameters of the solid solution between ?-miargyrite and smithite increase up to about 50% of AgSbS2 substitution in the smithite structure and then reveal a structural phase transition as a function of composition. Electron diffraction (TEM) data for ?-miargyrite is consistent with the space group A2/a , but for the compositions Ag(As0.1Sb0.9)S2 and Ag(As0.3Sb0.7)S2, the phases do not show good Laue zones and Kikuchi lines and the symmetry could be either monoclinic or triclinic. The variation in the DW factor derived from the EXAFS spectra for the first shell of S atoms surrounding As in Ag(As0.3Sb0.7)S2 tends to be smaller than for AgAsS2 indicating that the As environment in Ag(As0.3Sb0.7)S2 is more ordered than in Ag(As0.5Sb0.5)S2 and AgAsS2. This ordering indicates that with more substitution of Sb in AgAsS2, the monoclinic (A2/a) Ag(As0.5Sb0.5)S2 collapses around As atoms to a probable low-monoclinic or triclinic structure.