Фазовая диаграмма системы Au-La

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Au-La (Gold-Lanthanum) K.A. Gschneidner, Jr., F.W. Calderwood, H. Okamoto, and T.B. Massalski The assessed phase diagram for the La-Au system is based primarily on the work of [31Can], [71Mcm], and [74Mor]. The rare earth-rich intermediate phase is La2Au, which has the orthorhombic structure of the Co2Si type. This phase forms peritectically at 665 C from the melt and bLaAu. A eutectic occurs between La and La2Au at 561 C at 16 at.% Au. LaAu exists in two polymorphs and melts congruently at 1325 C. Both polymorphs have orthorhombic structures. The low-temperature form has the FeB- type structure and transforms at about 660 C to bLaAu with the CrB-type structure. LaAu2 exists in only the orthorhombic CeCu2-type structure and melts congruently at 1214 C. This compound forms a eutectic with bLaAu at 62.7 at.% Au and 1148 C. La14Au51, which melts at 1204 C, was found to exist in the same hexagonal structure as Gd14Ag51. It forms a eutectic with LaAu2 at 1054 C. The eutectic contains 69 at.% Au. Conflicting information on the existence of LaAu6 underscores the uncertainty of the Au-rich portion of the phase diagram. In the assessed diagram, LaAu6 is indicated by dashed lines to reflect the uncertainty in its existence as an equilibrium form. The temperature for the eutectic has been arbitrarily raised to 808 C to better conform with other rare earth-Au systems. A peritectic formation has been assumed for this compound. [75Joh] studied alloys of the form La100-xAux, where x ranged from 0 to 40 at.% . Samples were quenched from the liquid state at a cooling rate of ~106 C/s. A crystallite size less than six times the nearest neighbor distance indicated amorphous material. For 0 њ x њ 14, the crystalline phase designated b<291> had a bLa fcc structure with Au in solid solution. In the range 14њ x њ 18, liquid-quenched alloys contained the b<291> phase and an amorphous phase. A single amorphous phase was observed for alloys with 18 њ x њ 26; for 26 њ x њ 30, alloys contained both the amorphous phase and a new cubic phase. No amorphous material was obtained when the Au content exceeded 30 at.%. 31Can: G. Canneri, Metall. Ital., 23, 803 (1931). 71Mcm: O.D. McMasters, K.A. Gschneidner, Jr., G. Bruzzone, and A. Palenzona, J. Less-Common Met., 25, 135 (1971). 74Mor: J.M. Moreau and E. Parth‚, Acta Crystallogr. B, 30, 1743 (1974). 75Joh: W.L. Johnson, S.J. Poon and P. Duwez, Phys. Rev. B, 11, 150 (1975). Published in Phase Diagrams of Binary Gold Alloys, 1987. Complete evaluation contains 2 figures, 1 table, and 18 references. 1