Фазовая диаграмма системы Gd-Ge

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Gd-Ge (Gadolinium-Germanium) A.B. Gokhale and G.J. Abbaschian The assessed Gd-Ge phase diagram is based primarily on [80Ere], with supplementary information from an analysis of crystallographic data for the intermediate phases in the system. The following modifications have been incorporated in the diagram proposed by [80Ere]: the melting/allotropic transformation temperatures of the pure components have been changed to conform with the currently accepted values, Gd3Ge is indicated to exhibit a small (1 at.% Ge) homogeneity range, and an allotropic transformation, estimated to be below 600 C, is indicated for Gd3Ge5. The Gd-Ge system is characterized by the nearly stoichiometric hexagonal intermediate phase Gd5Ge3, the richest in Gd, which melts congruently at 1790 C; the nearly stoichiometric orthorhombic intermediate phase GdGe, which forms peritectically at 1570 C; the intermediate phase Gd2Ge3, which forms peritectically at 1415 C and which exhibits a homogeneity range from 59 to 61 at.% Ge; the intermediate phase Gd3Ge5, which decomposes peritectoidally at 808 C and exhibits a homogeneity range from 61.64 to 62.55 at.% Ge; the nearly stoichiometric orthorhombic intermediate phase GdGe2.57, which forms peritectically at 890 C and decomposes eutectoidally at 850 C; the eutectic between (Gd) and Gd5Ge3 at 1113 C and 11 at.% Ge, and another between (Ge) and GdGe2.57 at 860 C and 85 at.% Ge. The mutual terminal solid solubilities of the pure components have not been reported, but are probably very small. The liquidus was determined reliably by [80Ere] over the entire composition range. No thermodynamic data were available on the properties of the liquid solution; they were assessed by using the experimental solubility data of [ 80Ere]. The results indicate the process of mixing in the liquid to be exothermic. [79Bar] analyzed the functional dependence of the thermal expansion coefficient of Gd5Ge3 on temperature, and detected second-order transformations at 48 and 68 K. They concluded that the phase had a N‚el temperature (TN) corresponding to a change from paramagnetic to antiferromagnetic state of 68 K. [80Bar] measured TN for the phase by analyzing the temperature dependence of electrical resistivity, magnetization, and the linear expansion coefficient; their TN values (68, 68, and 70 K, respectively) were in good agreement with that of [79Bar]. By contrast, [67Bus] reported a TN of 48 K; it is likely that [67Bus] erroneously designated the temperature of the low-temperature transformation detected by [79Bar] as the N‚el temperature. According to [69Nar], the phase had a Weiss temperature of 54.8 K. For Gd5Ge4, [67Hol] reported N‚el and paramagnetic Curie temperatures of 15 and 94 K, respectively. 64Gla: E.I. Gladyshevskii, Zh. Strukt. Khim., 5, 568-575 (1964) in Russian; TR: J. Struct. Chem., 5, 523-529 (1964). 65Gla: E.I. Gladyshevskii and V.V. Burnashkova, Izv. Akad. Nauk SSSR, Neorg. Mater., 1, 1508-1512 (1965) in Russian; TR: Inorg. Mater., 1, 1374-1377 (1965). 66Sek: K. Sekizawa, J. Phys. Soc. Jpn., 21, 1137-1142 (1966). 67Bus: K.H.J. Buschow and J.F. Fast, Phys. Status Solidi, 21, 593-600 (1967). 67Hol: F. Holtzberg, R.J. Gambino, and T.R. McGuire, J. Phys. Chem. Solids, 28, 2283-2289 (1967). 67Ram: A. Raman and H. Steinfink, Inorg. Chem., 6(10), 1789-1791 (1967). 67Smi: G.S. Smith, A.G. Tharp, and Q. Johnson, Acta Crystallogr., 22, 940-943 ( 1967). 69Nar: K.S.V.L. Narasimiian, H. Steinfink, and E.V. Ganapathy, J. Appl. Phys., 40(1), 51-54 (1969). 79Bar: S.M. Barmin, R.P. Krentsis, P.V. Gel›d, and V.G. Batalin, Fiz. Tverd. Tela, 21, 3174-3176 (1979) in Russian; Sov. Phys. Solid State, 21, 1830-1831 ( 1979). 80Bar: S.M. Barmin, D.A. Emel›yanov, R.P. Krentsis, and P.V. Gel›d, Fiz. Tverd. Tela, 22, 1224-1226 (1980) in Russian; TR: Sov. Phys. Solid State, 22, 714- 715 (1980). 80Ere: V.N. Eremenko, V.G. Batalin, Yu.I. Buyanov, and I.M. Obushenko, Porosh. Met., 2, 40-45 (1980) in Russian; TR: Sov. Powder Metall. Met. Ceram., 19, 104- 108 (1980). Published in Bull. Alloy Phase Diagrams, 10(2), Apr 1989. Complete evaluation contains 2 figures, 2 tables, and 24 references. Special Points of the Gd-Ge System