Фазовая диаграмма системы Ge-Mg

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Ge-Mg (Germanium-Magnesium) A.A. Nayeb-Hashemi, R.W. Olesinski, G.J. Abbaschian, and J.B. Clark The equilibrium phases of the Mg-Ge system are (1) the liquid; (2) the terminal solid solution, (Mg), with negligible solid solubility of Ge in Mg; ( 3) the terminal solid solution, (Ge), (the solid solubility of Mg in Ge is very low); and (4) the Mg2Ge compound, a semiconductor, of essentially stoichiometric composition. The assessed phase diagram is based primarily on the thermal analysis of [68Gef] and [40Ray], with evaluation of the work of [ 41Kle], [66Bea], [66Eld], and [71Rao]. The eutectic composition and temperature on the Mg-rich side, L = (Mg) + Mg2Ge, was given by [68Gef] as 1.15 at.% Ge and 635.6 C, and on the Ge-rich side, L = Mg2Ge + (Ge), as 64.3 at.% Ge and 696.7 C. The melting point of Mg2Ge was placed at 1117.4 C by [68Gef]. Between the two eutectic points, the thermodynamic analysis of [66Eld], using the isopiestic technique for alloys, placed the liquidus curves at temperatures close to those of [68Gef]. At pressures higher than 2.06 MPa and at temperatures up to ~1500 C, Mg2X ( where X = Si, Ge, and Sn) exhibited polymorphic transformations. For magnesium germanide (Mg2Ge), its cubic Fm3m antifluoride structure transformed to the hexagonal crystal structure, after exposure to temperatures in the range of 600 to 1200 C and pressures of 2.53 to 5.57 MPa. The new structure acted as a semiconductor as well, but with a different resistivity than the cubic Mg2Ge. The Mg2Ge compound is a semiconductor with an energy gap of 0.74 eV. The high- temperature and pressure structure was noted to be indefinitely metastable at ambient conditions after the release of pressure. The calculated and the assessed Mg-Ge phase diagrams are in good agreement, with deviations of less than 10 C, except in a few areas. 40Ray: G.V. Raynor, J. Inst. Met., 66, 403-426 (1940). 41Kle: W. Klemm and H. Westlinning, Z. Anorg. Chem., 245, 365-380 (1941). 66Bea: P. Beardmore, B.W. Howlett, B.D. Lichter, and M.B. Bever, Trans AIME, 236, 102-108 (1966). 66Eld: J.M. Eldridge, E. Miller, and K.L. Komarek, Trans. AIME, 236, 1094-1098 (1966). 68Gef: R. Geffken and E. Miller, Trans. AIME, 242, 2323-2328 (1968). 71Rao: Y.K. Rao and G.R. Belton, Metall. Trans., 2, 2215-2219 (1971). Published in Phase Diagrams of Binary Magnesium Alloys, 1988, and Bull. Alloy Phase Diagrams, 5(4), Aug 1984. Complete evaluation contains 3 figures, 7 tables, and 28 references. 1