Фазовая диаграмма системы Ge-Hf

К оглавлению: Другие диаграммы (Others phase diargams)


Ge-Hf (Germanium-Hafnium) A.B. Gokhale and G.J. Abbaschian The assessed Hf-Ge phase diagram is based partially on the work of [60Now1] and in part on investigations not directly related to the phase equilibria but pertaining to the crystal structures of the intermediate phases. The temperatures measured by [60Now1] are only approximate. For example, they indicated the presence of a eutectic between HfGe2 and (Ge) at 945 C, i.e., higher than the currently accepted melting temperature for Ge (938.3 C). In this evaluation, this discrepancy has been corrected, and the eutectic is indicated to occur at a temperature somewhat lower than 938.3 C. The experimentally determined equilibria are shown by solid lines in the assessed diagram, while those indicated by broken lines are speculative, and are included only to complete the diagram. The broken lines were drawn based on assumed similarities between the Hf-Si and Hf-Ge systems. The key features of the Hf-Ge system are: tetragonal Hf3Ge, the richest in Hf; tetragonal Hf2Ge, which forms peritectically at ~2026 C; hexagonal Hf5Ge3, which melts congruently at 2200 C; tetragonal Hf3Ge2; the intermediate phases Hf5Ge4 and HfGe; orthorhombic HfGe2, the richest in Ge, which forms peritectically at 1744 C; and two eutectics, between (bHf) and Hf3Ge at 1775 C and ~10 at.% Ge, and between HfGe2 and (Ge) at ~930 C and ~98 at.% Ge. There are no reports on the homogeneity ranges of the intermediate phases. The maximum terminal solid solubility of Ge in (bHf) appears to be less than 1 at.% [60Now1]. The solid solubility of Hf in Ge has not been determined, but is likely to be small. Some ambiguity remains as to the total number of intermediate phases in the system. The following have been variously reported: Hf3Ge, Hf2Ge, Hf5Ge3, Hf3Ge2, Hf5Ge4, ~Hf6Ge5, HfGe, and HfGe2. All but Hf5Ge3 may be taken as established. However, some reservations may be noted regarding Hf5Ge3; the phase has been reported to be stable only in the presence of C [59Par] and C and O [60Now2]. Also, similar (D88) phases in the Zr-Si and Hf-Si systems appear to be ternary or higher order, and not strictly binary. However, Hf5Ge3 has been tentatively included in the assessed diagram following reports by [ 60Now1], [68Bon], [77Mar], and [82Zyu]. [65Ros] reported the presence of a phase that corresponded approximately to the stoichiometric composition Hf6Ge5. The composition is sufficiently close to that of HfGe, so the data of [65Ros] have been assigned to HfGe. [82Zyu] indicated the presence of Hf5Ge4, but not the HfGe. [77Mar] noted the presence of HfGe instead of Hf5Ge4 on the Hf-Ge-B ternary isotherm at 800 C, as did [60Now1] and [60Now2]. At present, there are insufficient data either to accept or discard the presence of either or both intermediate phases. However, in the Hf-Si system, [68Bru] noted the presence of Hf5Si4 and HfSi. Consequently, Hf5Ge4 and HfGe have both been tentatively included in the assessed diagram. [60Now1] reported a eutectic between (bHf) and Hf2Ge. However, [64Sch] later established the presence of Hf3Ge. Consequently, the eutectic reaction is indicated to occur between (bHf) and Hf3Ge in this evaluation. 57Smi: J.F. Smith and D.M. Bailey, Acta Crystallogr., 10, 341-342 (1957). 59Par: E. Parthe, Acta Crystallogr., 12, 559-560 (1959). 60Now1: H. Nowotny, H. Braun, and F. Benesovsky, Radex Rundsch., 6, 367-372 ( 1960) in German. 60Now2: H. Nowotny, F. Benesovsky, Monatsch. Chem., 91, 270-275 (1960) in German. 64Sch: K. Schubert, H.G. Meissner, and W. Rossteutscher, Naturwissenschaften, 51, 506-507 (1964) in German. 65Ros: W. Rossteutscher and K. Schubert, Z. Metallkd., 56(11), 813-822 (1965) in German. 68Bon: V.N. Bondarev, V.A. Podergin, and V.P. Perminov, Izv. Akad. Nauk SSSR, Neorg. Mater., 4, 1689-1693 (1968) in Russian. 68Bru: C.E. Brukl, Tech. Rep. AFML-TR-65-2, Part 1 (13), 72 pp (1968). 77Mar: M.A. Marko and Yu. Bu Kuzma, Izv. Akad. Nauk SSSR, Neorg. Mater., 13(5), 925 (1977) in Russian. 82Zyu: A.I. Zyubrik, R.R. Olenich, I.A. Mizak, and Ya.P. Yarmolyuk, Dopov. Akad. Nauk Ukr. RSR, Ser. A. Fiz.-Mat. Tekh. Nauki, (5), 78-81 (1982) in Ukrainian. Published in Bull. Alloy Phase Diagrams, 11(3), Jun 1990. Complete evaluation contains 1 figure, 4 tables, and 16 references. Special Points of the Hf-Ge System