Фазовая диаграмма системы Te-V

К оглавлению: Другие диаграммы (Others phase diargams)

Te-V (Tellurium-Vanadium) J.F. Smith The assessed phase diagram for the Te-V system is based largely on [86Ter], but that work terminated at 70 at.% V. To extend the diagram to 100 at.% V, data concerning a V-rich phase near TeV3 have also been included [68Mon]. The existence of TeV3 has not been confirmed, but there is no basis for rejection, because it was found in the only investigation of Te-V alloys in such a V-rich region. Equilibria in the central part of the system are complicated. All crystal structures in the composition range 35 to 50 at.% V are related to the NiAs- or CdI2-type structures. At high temperatures, the single-phase field in this composition range has a poorly defined V-rich boundary, but the composition variation within the phase is attributable to a random array of vacant V sites on alternate metal layers of the NiAs structure [58Gro, 67Che]; alternatively, this can be viewed as a partial filling of an intermediate layer in the CdI2 structure. At lower temperatures, the vacancies tend to order [67Che, 84Oht], and crystallographic transitions occur that result in crystallographically related structures of lower symmetry. These transitions must occur because of temperature-dependent changes in the bonding interactions. There is magnetic evidence [49Gal, 80Anz, 81Oht, 83Anz, 84Oht] that some d electrons of V remain unpaired and nonbonding while other d electrons participate with p electrons of Te to form bonds. Formation of Te8V5 from Te-rich Te4V3 appears to be by a first-order, congruent transformation. However, the transformation was not observable in either thermal or magnetic measurements, so it must be sluggish [84Oht]. The width of the phase field is not well established, but it must be narrow, not exceeding 1.5 at.% [84Oht]. The structure is a different monoclinic distortion of the NiAs structure [84Bro]. The Te8V5 phase is indicated to become antiferromagnetic near 52 K [80Anz]. A phase with the stoichiometry of TeV3 has been reported [68Mon] as forming from the reduction of mixed oxides by flowing hydrogen. The phase was reported as stable in air at ambient temperatures but was attacked at 600 C. It was also indicated as being insoluble in alcohol, benzol, and carbon disulfide. No information was given concerning its structural or metallurgical properties, nor was there any analytical data concerning the phase purity. Experiments should be made to confirm or refute the existence of this phase. 49Gal: F.M. Galperin and T.M. Perekalina, Dokl. Akad. Nauk SSSR, 69, 19-22 ( 1949); Chem. Abs. 44:994d. 58Gro: F. Gronvold, O. Hagberg, and H. Haraldsen, Acta Chem. Scand., 12, 971- 982 (1958). 67Che: M. Chevreton, Bull. Soc. Fr. Mineral Cristallogr., 90, 592-597 (1967) in French. 68Bru: S. Brunie and M. Chevreton, Bull. Soc. Fr. Mineral Cristallogr., 91, 422-427 (1968) in French. 68Mon: E. Montigne, Z. Anorg. Allg. Chem., 362, 329-330 (1969). 80Anz: S. Anzai and S. Ohta, J. Phys. Soc. Jpn., 49, 2079-2080 (1980). 81Oht: T. Ohtani, K. Hayashi, and M. Nakahira, Solid State Commun., 40, 629- 631 (1981). 83Anz: S. Anzai, S. Ohta, A. Yoshino, and M. Hatori, Phys. Status Solidi (b), 118, K99-K102 (1983). 84Bro: K.D. Bronsema, G.W. Bus, and G.A. Wiegers, J. Solid State Chem., 53, 415-421 (1984). 84Oht: T. Ohtani, S. Onoue, and M. Nakahira, Mater. Res. Bull., 19, 1367-1375 ( 1984). 86Ter: P. Terzieff, H. Ipser, and E. Wachtel, J. Less-Common Met., 119, 1-12 ( 1986). Published in Phase Diagrams of Binary Vanadium Alloys, 1989. Complete evaluation contains 4 figures, 3 tables, and 22 references. Special Points of the Te-V System