SULFUR–SELENIUM ISOMORPHOUS SUBSTITUTION AND MORPHOTROPIC TRANSITION IN THE Ag
3Au(Se,S)
2 SERIES
Yu.V. Seryotkin, G.A. Pal’yanova, N.E. Savva
Keywords: Uytenbogaardtite, fischesserite, solid-solution series Ag3 Au(Se, S)2, morphotropic transition, structural features
Abstract
Gold–silver sulfoselenides of the series Ag3 AuSex S2–x (x = 0.25; 0.5; 0.75; 1; 1.5) were synthesized from melts on heating stoichiometric mixtures of elementary substances in evacuated quartz ampoules. According to X-ray single-crystal analysis, the compound Ag3 AuSe0.5S1.5 has the structure of gold–silver sulfide Ag3AuS2 (uytenbogaardtite) with space group R 3 c . The volume of this compound is 1.5% larger than that of the sulfide analog. According to powder X-ray diffractometry, compounds Ag3 AuSe0.25S1.75 and Ag3AuSe
0.75S1.25 also show trigonal symmetry. Compounds Ag3AuSeS and Ag3AuSe 1.5S0.5 are structurally similar to the low-temperature modification of gold–silver selenide Ag3AuSe 2 (fischesserite) with space group I 4132. These data suggest the existence of two solid solutions: petzite-type cubic Ag3AuSe2–Ag
3AuSeS (space group I 4 132) and trigonal Ag3AuSe0.75S1.25 — Ag
3AuS2 (space group R 3 c ). It was found that fischesserite from the Rodnikovoe deposit (southern Kamchatka) contains 3.5–4 wt.% S. At the Kupol deposit (Chukchi Peninsula), fischesserite contains up to 2.5 wt.% S and uytenbogaardtite contains up to 5.3 wt.% Se. At the Ol’cha and Svetloe (Okhotskoe) deposits (Magadan Region), uytenbogaardtite contains up to 0.5 and 1.8 wt.% Se, respectively. Literature data on the compositions of silver—gold selenides and sulfides from different deposits were summarized and analyzed. Analysis of data available on the S and Se contents of natural fischesserite and uytenbogaardtite confirms the miscibility gap near composition Ag3AuSeS.
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