Фазовая диаграмма системы Au-Yb

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Au-Yb (Gold-Ytterbium) K.A. Gschneidner, Jr., F.W. Calderwood, H. Okamoto, and T.B. Massalski The Yb-Au system contains eight intermetallic compounds. The assessed phase diagram is based primarily on the work of [69Ian] and [70Ian], who investigated the phase relationships in this system. In the assessed diagram, the melting temperature for Au has been raised from the reported value of 1060 C [69Ian,70Ian] to 1064.43 C. Likewise, the melting point and the g = b transformation temperature for Yb are shown at 819 and 795 C, respectively. The Yb-rich compound, Yb7Au3, decomposes peritectically to the liquid and Yb2Au when heated above 661 C. Yb7Au3 has the hexagonal structure of the Fe3Th7 type. Yb2Au also decomposes peritectically; when heated above 712 C, it decomposes to the melt and Yb5Au3. Yb2Au crystallizes in the orthorhombic Co2Si-type structure. Both Yb5Au3 and Yb5Au4 form peritectically, the former at 861 C from the melt and Yb5Au4, and the latter at 926 C from the melt and bYbAu. Yb5Au3 crystallizes in the tetragonal Cr5B3-type structure, and Yb5Au4 crystallizes in the orthorhombic Sm5Ge4 type. YbAu has the highest melting point of any compound in the Yb-Au system (1292 C). [69Ian] observed complex behavior for YbAu. Only two thermal arrests were observed on cooling from the molten state to room temperature, one at 1292 C and one at 1278 C. Samples annealed below 400 C showed a complex structure, and another modification was present for samples annealed at 500 to 700 C. Above 900 C, CsCl-type structure appeared. A solid solution of Au in YbAu was found to exist for alloys between 50 and 53.5 at.% Au, with a maximum solubility at 1061 C. The low-temperature form crystallizes in the orthorhombic FeB-type structure. YbAu2 melts congruently at 1240 C and crystallizes in the tetragonal MoSi2- type structure. The congruently melting compound, YbAu3, melts at 1150 C and crystallizes in the orthorhombic Cu3Ti-type structure. The Au-rich compound, YbAu4, forms peritectically at 989 C from YbAu3 and the melt. It crystallizes in the tetragonal MoNi4-type structure. Four eutectic points occur in the Yb-Au system. The eutectic between (Yb) and Yb7Au3 exists at 18.5 at.% Au and 546 C; the eutectic between bYbAu and YbAu2 exists at 58.5 at.% Au and 1061 C; the eutectic between YbAu2 and YbAu3 exists at 72 at.% Au and 1131 C; and the eutectic between YbAu4 and Au exists at 89 at.% Au and ~ 817 C. The maximum solubility of Yb in (Au) is 6.9 at.% Yb at the eutectic temperature of 817 C [65Rid]. [69Ian] and [70Ian] reported that no solubility of Au in (Yb) was detected. [68Sad], who studied crystal chemistry of the Au-rich binary alloy phases of the heavy rare earths, observed that Yb behaves like a trivalent rare earth in Au solid solutions. This character is maintained in YbAu2, YbAu3, and YbAu4; only in YbAu is there an abnormally high atomic volume, which indicated a larger atomic size and a lower valency than in the other phases. 65Rid: P.E. Rider, K.A. Gschneidner, Jr., and O.D. McMasters, Trans. AIME, 233, 1488 (1965). 68Sad: Y. Sadagopan, B.C. Giessen, and N.J. Grant, J. Less-Common Met., 14, 279 (1968). 69Ian: A. Iandelli and A. Palenzona, J. Less-Common Met., 18, 221 (1969). 70Ian: A. Iandelli and A. Palenzona, Les Elements des Terres Rares, Vol. 1, Centre National de la Recherches Scientifique, Paris, 159 (1970) in French. Published in Phase Diagram of Binary Gold Alloys, 1987. Complete evaluation contains 2 figures, 2 tables, and 15 references. 1