Фазовая диаграмма системы S-V

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As-V (Arsenic-Vanadium) J.F. Smith No phase diagram has been published for the As-V system, and the type of information available does not justify proposing one. However, an appreciable amount of information is available concerning the number and types of phases that must ultimately be incorporated into such a diagram. A monoclinic phase with the formula As2V has been reported [64Hul] and confirmed [65Mei]. Existence of the AsV phase at equiatomic stoichiometry is well established. Although it has been reported to decompose under vacuum at temperatures exceeding 1000 C, no vapor pressure measurements are available, and the phase stability under an As vapor pressure of 1.013 bar is not known. There is no appreciable range of homogeneity, and the stoichiometry has been confirmed by pycnometric density measurements. Combined neutron and X-ray diffraction data indicate no structural change between -269 and 1000 C [72Sel]. An orthorhombic phase with the stoichiometry As3V4 was initially reported as isostructural with As3Nb4 [72Yvo]. Later investigations accepted this structure as the lower temperature polymorph, but found an additional higher temperature monoclinic form [74Ber]. The temperature of the transition between the structures is apparently above 1050 C, but a more precise value needs to be determined. The existence of a tetragonal phase near the stoichiometry As2V3 was found [ 74Ber], with a negligible range of homogeneity. A phase with the composition As3V5 was found to have tetragonal symmetry isomorphous with W5Si3 [66Bol], with an appreciable range of homogeneity. The structure has been confirmed by [76Ber]. This phase is the only arsenide known to have the W5Si3-type structure. This tetragonal polymorph is the form of As3V5 stable at lower temperatures. Two other polymorphs (both orthorhombic) are known to occur at higher temperatures [76Ber]. Because one of these orthorhombic polymorphs has been found only in arc-melted alloys, it may be a metastable form. A phase at the stoichiometry AsV2 was first reported by [41Mor]. It was found to form from the decomposition of AsV above 1000 C under vacuum and to melt at 1345 C [41Mor]. The existence of a cubic Cr3Si-type phase in the As-V system is well established [55Bac, 65Mei]. 41Mor: A. Morette, Compt. Rend., 212, 639-641 (1941) in French. 55Bac: K. Bachmayer and H. Nowotny, Monatsh. Chem., 86, 741-744 (1955) in German. 64Hul: F. Hulliger, Nature, 204, 775 (1964). 65Mei: H.G. Meissner and K. Schubert, Z. Metallkd., 56, 523-538 (1965) in German. 66Bol: H. Boller and H. Nowotny, Monatsh. Chem., 97, 1053-1058 (1966) in German. 72Sel: K. Selte, A. Kjekshus, and A.F. Andresen, Acta Chem. Scand., 26, 4057- 4062 (1972). 72Yvo: K. Yvon and H. Boller, Monatsh. Chem., 103, 1643-1650 (1972) in German. 74Ber: R. Berger, Acta Chem. Scand. A, 28, 771-778 (1974). 76Ber: R. Berger, Acta Chem. Scand., 30, 363 (1976). Published in Phase Diagrams of Binary Vanadium Alloys, 1989. Complete evaluation contains 2 tables and 15 references. 1