Фазовая диаграмма системы Cr-Pt

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Cr-Pt (Chromium-Platinum) M. Venkatraman and J.P. Neumann The assessed Cr-Pt phase diagram is based primarily on the experimental data of [73Wat], and is essentially the same as the diagram given in [Metals]. The Cr-Pt system is characterized by a broad homogeneity range of the (Pt) terminal solid solution and by the presence of three ordered intermediate phases-Cr3Pt, CrPt, and CrPt3. The existence of CrPt requires clarification. The liquidus and solidus of the (Pt) phase from 30 to 100 at.% Pt are taken from [30Mul] and [73Wat], respectively. Both investigations clearly indicate a maximum melting point of the (Pt) phase at ~80 at.% Pt. The composition and the temperature of the eutectics are taken from [73Wat]. However, the syntectic decomposition of Cr3Pt, tentatively suggested by [73Wat], is believed to be unlikely. Further studies are needed to clarify the liquid- solid equilibria in this region. The solubility of Pt in (Cr) reported by [55Rau] as 2.5 at.% Pt at 900 C is in good agreement with the selected solvus curve. [73Wat] observed a broad homogeneity range of the (Pt) phase, which extends from ~29 to 100 at.% Pt at 1530 C. Cr3Pt has the ordered cubic A15-type structure; it occurs slightly off the ideal stoichiometric composition at ~20 at.% Pt. The existence of an ordered fcc phase, CrPt3, that forms from the high- temperature disordered fcc (Pt) phase below 1200 C has been firmly established. CrPt3 has the L12-type (AuCu3) structure; it occurs over a wide composition range, from ~34 to ~85 at.% Pt. The ordering reaction is very fast, and the disordered high-temperature phase can be retained only partially by quenching [73Wat]. The maximum of the order-disorder transformation occurs at ~1130 C and ~67 at.% Pt. According to [73Wat], the ordered fcc L12-type structure of CrPt3 changes with increasing Cr concentration continuously to an ordered pseudo-cubic L10-type structure at the composition CrPt. Although CrPt shows the ordered layer arrangement of the L10 structure, the tetragonal distortion, which is typical of this structure, could not be observed [73Wat]. However, thin film studies of the Cr-Pt system below 600 C indicated a small tetragonal distortion of the CrPt phase, as well as the presence of a two-phase region between CrPt and CrPt3 [78Bag]. The results of the thin film studies are tentatively indicated by dashed lines in the assessed diagram. Small additions of Pt increase the N‚el temperature of pure Cr (311.5 K) rapidly to 440 K (0.6 at.% Pt) [80But], 583 K (2 at.% Pt) [68Kus], and 460 K ( 5 at.% Pt) [79Ole]. In contrast to the disordered (Pt) solid solution, which is paramagnetic, the ordered CrPt3 (L12) phase exhibits strong spontaneous magnetization [77Got]. According to [63Pic], the CrPt3 phase is ferrimagnetic and not ferromagnetic, as had been concluded by other investigators. The Curie temperature of the CrPt3 phase increases with increasing Cr concentration from -273 C (0 K) at ~83 at.% Pt [68Kus] to ~900 C at 52 at.% Pt. The saturation magnetization has a maximum near the stoichiometric composition CrPt3 [77Got]. The spontaneous magnetization decreases with increasing Cr concentration and the ferrimagnetic behavior changes at ~52 at.% Pt [35Fri, 68Kus] to the antiferromagnetic behavior of the CrPt (L10) phase [73Bes]. No N‚el point was observed by [73Bes] for CrPt up to 1300 C. 30Mul: L. MЃller, Ann. Phys. (Leipzig), 7(5), 9-47 (1930) in German. 35Fri: E. Friederich and A. Kussmann, Phys. Z., 36(6), 185-192 (1935) in German. 40Geb: E. Gebhardt and W. K”ster, Z. Metallkd., 32, 262-264 (1940) in German. 55Rau: E. Raub and W. Mahler, Z. Metallkd., 46, 210-215 (1955) in German. 56Gre: P. Greenfield and P.A. Beck, Trans. AIME, 206, 265-276 (1956). 63Pic: S.J. Pickart and R. Nathans, J. Appl. Phys., 34(4), 1203-1204 (1963). 68Kus: A. Kussmann, K. MЃller, and E. Raub, Z. Metallkd., 59, 859-863 (1968) in German. 68Reu: E.C. van Reuth and R.M. Waterstrat, Acta Crystallogr. B, 24, 186-196 ( 1968). 73Bes: M.J. Besnus and A.J.P. Meyer, Phys. Status Solidi (b), 58, 533-542 ( 1973). 73Wat: R.M. Waterstrat, Metall. Trans., 4, 1585-1592 (1973). 77Got: T. Goto, J. Phys. Soc. Jpn., 43, 1848-1853 (1977). 78Bag: J. Baglin, J. Dempsey, F. d'Heurle, W. Hammer, and S. Zirinsky, Proc. Electrochem. Soc., 78-2, 185-198 (1978). 79Ole: A. Oles and A. Bombik, Phys. Status Solidi (b), 92, K81-K83 (1979). 80But: A.K. Butylenko and V.V. Nevdacha, Dop. Akad. Nauk Ukr. RSR A, Fiz.-Mat. Tekh., 42(5) 66-69 (1980) in Ukrainian. Published in Bull. Alloy Phase Diagrams, 11(1), Feb 1990. Complete evaluation contains 2 figures, 3 tables, and 37 references. Special Points of the Cr-Pt System