Фазовая диаграмма системы Gd-Si

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Gd-Si (Gadolinium-Silicon) A.B. Gokhale and G.J. Abbaschian There has been no single, comprehensive investigation of the equilibria in the Gd-Si system. Consequently, the assessed phase diagram is based on results from several studies carried out over limited composition and/or temperature ranges; in some instances, data not directly related to the phase equilibria, but pertaining mainly to the crystal structure of the intermediate phases, were used. The liquidus has not been determined, but has been sketched in by the present evaluators. The known features of the Gd-Si system may be summarized as: (1) nearly stoichiometric, hexagonal Gd5Si3, richest in Gd; (2) nearly stoichiometric, orthorhombic Gd5Si4; (3) orthorhombic GdSi; (4) hexagonal GdSi2-x, with a homogeneity range of 2.5 (60 to 62.5) at.% Si; (5) orthorhombic GdSi2, with a homogeneity range of 2.8 (64 to 66.8) at.% Si, which polymorphically transforms to tetragonal at 400 с 25 C; and (6) two eutectic reactions-one between (Gd) and Gd5Si3 at 1070 C and 15.2 at.% Si [64Cop] and one between Gd5Si3 and Gd5Si4 at 1060 с 20 C and an undetermined composition [76Gan]. Based on the interactions of Si with other RE elements, the process of liquid mixing in the Gd-Si system is likely to be exothermic; the presence of five intermediate phases in the system also suggests this trend. [81Tu] measured the Schottky barrier heights of GdSi2 formed on n-type and p- type Si wafers. They noted that in other disilicides, the Schottky barrier height could be correlated with the eutectic temperature between MSi2 and (Si), where M denotes the other component. Based on this information, they speculated that another eutectic reaction may exist in this system, probably in the temperature range 1300 to 1800 C. Examination of other RE-Si systems ( Y-Si, Ce-Si, and Nd-Si) shows that a eutectic reaction of this type occurs in each system. Also, the eutectic compositions and temperatures are very close to 85 at.% Si and 1200 C, respectively. Based on this information, a eutectic reaction has been tentatively included between GdSi2 and (Si) at 1200 C and 85 at.% Si. Two additional eutectic reactions are shown in the assessed diagram. These are purely speculative and have been included only to complete the diagram. [64Cop] indicated the maximum solid solubility of Si in (Gd) to be less than 1 at.%. The solid solubility of Gd in (Si) has not been determined, but is probably very small. 59Per: J.A. Perri, I. Binder, and B. Post, J. Phys. Chem., 63, 616-619 (1959). 64Cop: M. Copeland and H. Kato, Physics and Material Problems in Reactor Control Rods, IAEA, Vienna (1964). 67May: I. Mayer, E. Yanir, and I. Shidlovsky, Inorg. Chem., 6(4), 842-844 ( 1967). 68Ram: A. Raman, Trans. Indian Inst. Met., 5-8 (Dec 1968). 72Igl: J.E. Iglesias and H. Steinfink, J. Less-Common Met., 26, 45-52 (1972). 76Gan: E.V. Ganapathy, K. Kugimiya, H. Steinfink, and D.I. Tchernev, J. Less- Common Met., 44, 245-258 (1976). 81Tu: K.N. Tu, R.D. Thompson, and B.Y. Tsaur, Appl. Phys. Lett., 38, 626-628 ( 1981). Published in Bull. Alloy Phase Diagrams, 9(5), Oct 1988. Complete evaluation contains 1 figure, 3 tables, and 23 references. Special Points of the Gd-Si System