Fe-Nd-Sb (Iron-Neodymium-Antimony)

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Section II: Phase Diagram Evaluations

Fe-Nd-Sb (Iron-Neodymium-Antimony) V. Raghavan

Recently, [2007Zen] determined an isothermal section for this ternary system at 500 C, which depicts ﬁve ternary compounds.

notation s1, s2, etc. is adopted here in place of the symbols A, B, etc. used by [2007Zen]. The compounds found for the ﬁrst time by [2007Zen] are s2 (B) and s4 (D).

Binary Systems

Isothermal Sections

The Fe-Nd phase diagram depicts two intermediate phases: Fe17Nd2 (Th2Zn17-type rhombohedral) and Fe17Nd5 (hexagonal, space group P63/mcm). The Fe-Sb phase diagram [1997Ric] has two intermediate phases: FeSb1-x (41-49 at.% Sb; B81, NiAs-type hexagonal) and FeSb2 (C18, marcasite-type orthorhombic). The Nd-Sb phase diagram [1992Cac] has the following intermediate phases: Nd2Sb (La2Sb-type tetragonal), Nd5Sb3 (D88, Mn5Si3-type hexagonal), Nd4Sb3 (D73, Th3P4-type cubic), NdSb (B1, NaCl-type cubic), and NdSb2 (SmSb2-type orthorhombic).

With starting metals of 99.9% Fe, 99.8% Nd, and 99.95% Sb, [2007Zen] arc-melted or induction-melted alloys under Ar atm. The ﬁnal anneal at 500 C for 200 h was followed by quenching in liquid nitrogen. The phase equilibria were studied with x-ray powder diffraction and scanning electron microscope equipped with energy dispersive analysis. The isothermal section constructed by [2007Zen] is redrawn in Fig. 1. No solubility of the third component in the binary compounds of the system was found. The FeSb-Sb-NdSb region of the system was investigated at 597 C by [1999Sol]. With starting metals of purity of 99.99% Fe, 99.9% Nd, and 99.999% Sb, [1999Sol] arcmelted under Ar atm alloy samples, which were annealed at 597 C for 2 weeks and quenched in water. The phase equilibria were studied with X-ray powder diffraction. The isothermal section at 597 C (870 K) constructed by [1999Sol] for the FeSb1-x-Sb-NdSb region is redrawn in Fig. 2. The ternary phases s3 (NdFe1-xSb2) and s5

Ternary Compounds Table 1 lists the structural characteristics of the ﬁve ternary compounds of this system: Nd6Fe13Sb (s1 or A), NdFe2.5Sb2 (s2 or B), NdFe1-xSb2 (s3 or C) (x 0.35), NdFeSb3 (s4 or D), and NdFe4Sb12 (s5 or E) [2007Zen]. The

Table 1

Fe-Nd-Sb crystal structure and lattice parameter data [2007Zen]

Phase Nd6Fe13Sb (s1 or A)

NdFe2.5Sb2 (s2 or B)

NdFe1-xSb2 (s3 or C)

NdFeSb3 (s4 or D)

NdFe4Sb12 (s5 or E)

448

Composition, at.% 65 Fe 30 Nd 5 Sb 45.4 Fe 18.2 Nd 36.4 Sb Fe 18 Nd 27 Sb 55 20 Fe 20 Nd 60 Sb 23.5 Fe 5.9 Nd 70.6 Sb

Pearson symbol …

Space group

Prototype

Lattice parameter, nm

I4/mcm

Co11Ga3La6

a = 0.80903 c = 2.31923

…

…

…

…

tP8

P4/nmm

CuSi2Zr

a = 0.43514 c = 0.96518

…

Pbcm

CeNiSb3

cI34

Im3

Fe4LaP12

a = 1.26823 b = 0.61670 c = 1.81850 a = 0.9130

Journal of Phase Equilibria and Diffusion Vol. 29 No. 5 2008

Phase Diagram Evaluations: Section II

Fig. 1 Fe-Nd-Sb isothermal section at 500 C [2007Zen]. Narrow two-phase regions are omitted

(NdFe4Sb12) are present. The ternary compound s4 (NdFeSb3), which falls within this region, was not found at 597 C b

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