Фазовая диаграмма системы Cd-S

К оглавлению: Другие диаграммы (Others phase diargams)

Cd-S (Cadmium-Sulfur) R.C. Sharma and Y.A. Chang The Cd-S system is characterized by a congruently melting intermediate phase, aCdS, at 50 at.% S. There are two eutectics very close to pure Cd and pure S, respectively, and most likely a liquid miscibility gap and a monotectic in the aCdS-S region. The assessed phase diagram is based on thermodynamic modeling and calculations. The liquidus was determined by [63Woo] up to ~25 at.% S on the Cd-rich side at a single composition of ~99.9 at.% S on the S-rich side. There are no other measurements. Based on the present evaluators' experience with other metal-S systems and the similarities between Cd-Se and Cd-S systems, a liquid miscibility gap and a monotectic reaction are proposed in the aCdS-S region of the assessed diagram. The assessed liquidus is based on thermodynamic calculations. The monotectic temperature is arbitrarily fixed at 1000 C (lower than the critical point of S) and the monotectic composition is based on the present evaluators' calculations. The assessed monotectic temperature and composition are, therefore, subject to considerable error. The mutual solid solubilities of Cd and S have not been experimentally determined. They are most likely negligible. In the solid state, S exists in two allotropic forms. The low-temperature form (aS) transforms to (bS) at 95.5 C. The aCdS phase is essentially stoichiometric and melts congruently. The aCdS phase (B4 structure) transforms to bCdS phase (B1 structure) at high pressures [66Osu]. The transformation occurs at ~22.5 kbar at room temperature. The aCdS to bCdS transition at room temperature is accompanied by ~20% decrease in volume [66Osu]. CdS prepared under certain conditions by vapor deposition or from aqueous solutions may form as a metastable fcc (B3-type) phase rather than the stable hexagonal (B4-type) phase [64Sha]. [62Pas] examined CdS crystals formed by reacting Cd vapor with H2S gas at 650 C and found CdS to be hexagonal with 24- layer (24H) packing. 62Pas: A.S. Pashinkin and L.M. Kovba, Kristallografiya, 7, 316-318 (1962) in Russian; TR: Sov. Phys. Crystallogr., 7, 247-248 (1962). 63Woo: H.H. Woodbury, J. Phys. Chem. Solids, 24, 881-884 (1963). 64Cor: J.A. Corll, J. Appl. Phys., 35, 3032-3033 (1964). 64Sha: K.V. Shalimova, A.F. Andrushko, V.A. Dmitriev, and L.P. Pavlov, Sov. Phys. Crystallogr., 8, 628-720 (1964). 66Osu: J. Osugi, K. Shimizu, T. Nakamura, and A. Onodera, Rev. Phys. Chem. Jpn. , 36(2), 59-73 (1966). Submitted to the APD Program. Complete evaluation contains 6 figures, 6 tables, and 25 references. 1