The gold/selenium system and some gold seleno-tellurides

Abstract

The phase relationships in the gold/selenium system have been examined using X-ray powder diffraction techniques and differential thermal analysis. Only one stable phase, α-AuSe, is formed. A metastable modification of this compound, β-AuSe, is also formed by reaction of the elements. Both forms are monoclinic:α-AuSe: space group C2, Cm, or C2/m; a = 12.21 ± 2, b = 3.693 ± 4, c = 8.434 ± 6 Å, β = 103.20 ± 3°; cell content, 8(AuSe).β-AuSe: primitive monoclinic (space groups P2 1 or P2 1 /m are likely); a = 6.27 ± 1, b = 3.668 ± 4, c = 8.35 ± 1 Å, β = 105.95 ± 13°; cell content, 4(AuSe).Both modifications decompose peritectoidally at ca. 400 °C. Gold and selenium form a monotectic at 754 °C at a composition just above 50 at. % selenium; some evidence was obtained for the presence of two liquid phases above the monotectic.Tellurium does not substitute in the AuSe lattice to a detectable extent. However, a ternary phase which includes the composition Au 2 SeTe is formed. Au 2 SeTe is primitive orthorhombic with a = 8.924 ± 6, b = 7.56 ± 1, c = 5.741 ± 8 Å. The cell contains 4 formula units. Selenium will substitute for at least 15 at. % of the tellurium atoms in the monoclinic AuTe 2 calaverite lattice at ca. 400 °C.