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Phase Diagram Evaluations: Section II

Fe-P-Y (Iron-Phosphorus-Yttrium) V. Raghavan

A partial isothermal section for this system at 800 °C was determined recently by [2002Ori]. The section depicts two ternary compounds.

Binary Systems A partial phase diagram is known for the Fe-P system [1982Kub]. The intermediate compound Fe 3 P forms through a peritectic reaction at 1166 °C between liquid and Fe2P. Fe2P forms congruently at 1370 °C. Fe3P is body centered tetragonal with the Ni3P-type structure. Fe2P has the hexagonal C22 structure. The other intermediate phases at higher P contents are FeP (orthorhombic MnP type), FeP2 [orthorhombic FeS2 (marcasite) type], and FeP4 (monoclinic). The Fe-Y phase diagram [1992Zha] depicts four intermediate phases with limited or no homogeneity ranges: Y2Fe17, Y6Fe23, YFe3, and YFe2. See [1992Zha] for crystal structure data. The Y-P phase diagram is not known. The compound YP has the cubic NaCl type structure.

Ternary Isothermal Section With starting materials of 99.95 Fe, 99.98 P, and 99.5 Y (all at.%), Orishchin et al. [2002Ori] melted 17 ternary alloy compositions in an arc furnace under Ar atm. The alloys were finally annealed at 800 °C for 500 h and quenched in water. The phase equilibria were studied mainly by x-ray

powder diffraction, supplemented by metallography and electron probe microanalysis. The isothermal section at 800 °C determined by [2002Ori] up to 50 at.% P is redrawn in Fig. 1 to agree with the accepted binary data. Two ternary compounds are stable at this temperature. Y2Fe12P7 (denoted ␶1 here) has the hexagonal Zr2Fe12P7 type of structure. The crystal structure of YFe5P2 (the experimentallydetermined composition is YFe4.8P1.8), denoted ␶2 in Fig. 1, was not resolved. The ternary compound YFe5P3 [1984Jei] was not found at this temperature. The compound YP forms tie lines with the two ternary compounds as well as with all the binary compounds (except Fe3P). The solubility of the third component in the binary phases is negligible. Y2Fe17, which has two crystal modifications, was found to have the hexagonal Th2Ni17 type structure at 800 °C [2002Ori]. References 1982Kub: O. Kubaschewski: “Iron-Phosphorus” in Iron – Binary Phase Diagrams, Springer-Verlag, Berlin, 1982, pp. 84-86. 1984Jei: W. Jeitschko, U. Meisen, and U.D. Scholtz: “Ternary Lanthanoid Iron Phosphides With YCo5P3 and Zr2Fe12P7-type Structures,” J. Solid State Chem., 1984, 55, pp. 331-36. 1992Zha: W. Zhang, G. Liu, and K. Han: “The Fe-Y (IronYttrium) System,” J. Phase Equilibria, 1992, 13(3), pp. 304-08. 2002Ori: S.V. Orishchin, O.V. Zhak, S.L. Budnik, and Yu.B. Kuzma: “The Y-Fe-P System,” Zhur. Neorg. Khim., 2002, 47(9), pp. 1541-44 (in Russian); TR: Russ. J. Inorg. Chem., 2002, 47(9), pp. 1411-14.

Fig. 1 Fe-P-Y isothermal section at 800 °C [2002Ori]. Narrow two-phase regions around tie-triangles are omitted

Journal of Phase Equilibria and Diffusion Vol. 25 No. 2 2004

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