Фазовая диаграмма системы Ag-Te

К оглавлению: Другие диаграммы (Others phase diargams)

Ag-Te (Silver-Tellurium) I. Karakaya and W.T. Thompson The condensed phases of the Ag-Te system are the liquid, L, with a miscibility gap and the solid phases: fcc (Ag); cph (Te); and three compounds, Ag2Te, Ag1. 9Te, and Ag5Te3. The assessed phase diagram is shown at standard atmospheric pressure. The low-temperature monoclinic aAg2Te form is stable up to 145 C; an intermediate fcc bAg2Te transforms to bcc gAg2Te at 689 C. These temperatures for allotropic transformation apply when Ag2Te has a slight excess of Te. Two different crystallographic structures are thought to exist for Ag5Te3. Hexagonal aAg5Te3 transforms into the b form at 295 C in the presence of excess Te [64Hon]. Part of the L/L+g phase boundary was calculated from the thermodynamic data for Te evaporation [77Bar]. The vapor phase was assumed to be composed of an ideal mixture of equilibrium concentrations of Te, Te2, and Te5, with Te2 being the most abundant over the temperature range in the assessed diagram. With the exception of the miscibility gap, the phase boundaries for the liquid field were established from cooling curves [10Pel, 16Chi]. The presence of a miscibility gap was established by [40Kra] and [66Kra]. Solid solubility of Te in (Ag) [39Koe] and that of Ag in (Te) [39Koe] are negligible. The distribution coefficients from segregation studies [63Kuj, 65Kuj] indicate the maximum Ag solubility in (Te) to be on the order of 10-4 at.%. In a recent review [80Gla], the Te solubility in (Ag) was suggested to be about 5 x 10-3 at.%. The mineral empressite, AgTe, stable below 210 C, has approximately 50% composition [64Hon]. However, it has not been possible to produce this phase by direct combination of the elements [64Hon]. It is presumed that this is a metastable phase at standard atmospheric pressure. A simple cubic metastable silver telluride phase with variable composition in the above range, AgTe4-AgTe2.33, has been reported to form by rapid cooling from the melt [62Luo]. This phase is completely decomposed by heating at 110 C for 15 min [62Luo]. AgTe3 is stable above 358 C when the pressure exceeds 0.4 GPa [83Ran]. Ag2TeII is stable at pressures of 2200 to 2500 kPa. Ag2TeIII becomes stable when the pressure exceeds 2500 kPa. 10Pel: G. Pellini and E. Quercigh, Atti. Accad. Naz. Lincei, 19, 415-421 (1910) in Italian. 16Chi: M. Chikashige and I. Saito, Mem. Coll. Sci. Kyoto Univ., 1, 361-368 ( 1916) in German. 39Koe: V. Koern, Naturwissenschaften, 27, 432 (1939) in German. 40Kra: F.C. Kracek and C.J. Ksanda, Trans. Am. Geophys. Union, 363 (1940). 62Luo: H.L. Luo and W. Klement, J. Chem. Phys., 36, 1870-1874 (1962). 63Kuj: R.V. Kujawa, Z. Phys. Chem. (Leipzig), 222, 325-329 (1963) in German. 64Hon: R.N. Honea, Am. Mineralogist, 49, 325-338 (1964). 65Kuj: R.V. Kujawa, Phys. Status Solidi, 12, 169-180 (1965) in German. 66Kra: F.C. Kracek, C.J. Ksanda, and L.J. Cabri, Am. Mineralogist, 51, 14-28 ( 1966). 77Bar: I. Barin, O. Knacke, and O. Kubaschewski, Thermochemical Properties of Inorganic Substances (Supplement), Springer-Verlag, Berlin (1977). 80Gla: V.M. Glazov and A.S. Burkhanov, Izv. Akad. Nauk SSSR, Neorg. Mater., 16, 373-391 (1980). 83Ran: K-J. Range and M. Thomas, Mater. Res. Bull., 18, 1195-1202 (1983). Submitted to the APD Program. Complete evaluation contains 5 figures, 6 tables, and 50 references. Special Points of the Ag-Te System