Фазовая диаграмма системы Ga-V

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Ga-V (Gallium-Vanadium) J.F. Smith The equilibria and crystallography of the V-Ga system are affected by relatively minor amounts of interstitial contaminants, particularly oxygen and nitrogen. Consequently, significant differences exist among published diagrams. As such, the assessed V-Ga phase diagram represents a critical selection from the composite of available data. It is based primarily on a review of the work of [63Sch], [64Hau], [64Sav], [65Mei], [66Mai], [67Sav], and [68Saz]. In the composition range 0 to 40 at.% Ga, the essential features of the equilibria are well established; the uncertainties are in the precision associated with the temperature and composition coordinates of the phase boundaries. There is evidence for the existence of five intermediate phases, and peritectic melting occurs for both V2Ga5 and V8Ga41. However, in the composition range 40 to 95 at.% Ga in the temperature interval 900 to 1300 C, a diversity of equilibria have been reported, and the details, particularly the monotectic reaction, are more uncertain. V3Ga has the cubic Cr3Si-type structure with a superconducting transition near 16.8 K. Below room temperature, the Cr3Si-type structure of V3Ga persists down to about 20 K, where the phase undergoes a martensitic transformation analogous with the transformation in other V3X and Nb3X superconductors. There is general agreement that eutectoidal equilibrium exists between V3Ga, the bcc terminal solution, and V6Ga5 at some temperature in the range 1000 to 1100 C. V6Ga5 is hexagonal and isostructural with aTi6Sn5. A congruent solid- state transformation to the bcc terminal solution of Ga in (V) has been reported for the phase, but a peritectoidal decomposition of V6Ga5 to form the bcc terminal solution plus a more Ga-rich phase near V6Ga7 also has been reported and is more likely. Because of a high probability of oxygen contamination, a phase reported at the stoichiometry of V5Ga3 [67Sav] is unlikely to be a true equilibrium phase in the binary system. The decomposition of V6Ga7 at 1015 C was reported to be by eutectoidal reaction and at 1150 C by peritectic reaction. The temperatures for these reactions in the assessed diagram represent reasonable compromises among the composite data; most of the investigations show the stoichiometry of the phase at both the eutectoidal and peritectic reactions as being nearer to V6Ga7 than VGa. The monotectic reaction in association with V6Ga7 is the least certain figure of the diagram. V2Ga5 is tetragonal with the Mn2Hg5-type structure. This phase undergoes peritectic melting between 1015 and 1085 C, and an eclectic temperature of 1050 с 20 C was selected for the assessed phase diagram. Solubility of V in solid (Ga) is virtually nil, so the equilibrium between solid (Ga), V8Ga41, and the liquid occurs, for practical purposes, at the melting point of Ga. 63Sch: K. Schubert, K. Frank, R. Goble, A. Maldonado, A. Raman, and W. Rossteutscher, Naturwissenschaften, 50, 41 (1963). 64Hau: J.J. Hauser, Phys. Rev. Lett., 13, 470-471 (1964). 64Sav: E.M. Savitskii, P.I. Kripyakevich, V.V. Baron, and Yu. V. Efimov, Zh. Neorg. Khim., 9(5), 1155 (1964) in Russian; TR: Russ. J. Inorg. Chem., 9, 631- 633 (1964). 65Mei: H.G. Meissner and K. Schubert, Z. Metallkd., 56, 475-484 (1965). 66Mai: R.G. Maier, Y. Uzel, and H. Kandler, Z. Naturforsch., 21, 531-540 (1966) . 67Sav: E.M. Savitskii, P.I. Kripyakevich, V.V. Baron, and Yu.V. Efimov, Izv. Akad. Nauk SSSR, Neorg. Mater., 3 35-42 (1967) in Russian; TR: Inorg. Mater. ( USSR), 3(1), 45 (1967). 68Saz: N.P. Sazhin, N.S. Vorobeva, Y.N. Kunakov, and G.N. Ronami, Dokl. Akad. Nauk SSSR, 178, 341-344 (1968) in Russian; TR: Sov. Phys. Dokl., 13(1) 66-70 ( 1968). Published in Phase Diagrams of Binary Vanadium Alloys, 1989. Complete evaluation contains 1 figure, 1 table, and 29 references. 1