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ection II: Phase Diagram Evaluations

Dy-Fe-Ge (Dysprosium-Iron-Germanium) V. Raghavan

Recently, [2009Zhu] determined an isothermal section for this system at 500 °C, which depicts five ternary compounds.

Binary Systems The Dy-Fe phase diagram [Massalski2] shows the following intermetallic compounds: Fe17Dy2 (Ni17Th2-type hexagonal), Fe23Dy6 (D8a, Mn23Th6-type cubic), Fe3Dy (Be3Nb-type rhombohedral), and Fe2Dy (C15, MgCu2-type cubic). The Dy-Ge phase diagram [Massalski2, 2009Zhu] depicts the following intermediate phases: Dy5Ge3 (D88, Mn5Si3-type hexagonal), Dy5Ge4 (Ge4Sm5-type orthorhombic), DyGe (Bf, CrB-type orthorhombic), Dy2Ge3 (C32, AlB2-type hexagonal), Dy3Ge5 (Ge5Y3-type orthorhombic), DyGe2 (Ge2Tb-type orthorhombic), and DyGe3 (DyGe3-type orthorhombic). In the Fe-Ge phase diagram [Massalski2], the intermediate phases found stable at 500 °C are: Fe3Ge (L12, AuCu3-type cubic), Fe5Ge3 (B81, NiAs-type hexagonal), Fe6Ge5 (Fe6Ge5-type monoclinic, space group C2/m), FeGe and FeGe2 (C16, CuAl2-type tetragonal).

Ternary Compounds [2009Zhu] identified five ternary compounds at 500 °C. DyFe4Ge2 (s1) has the ZrFe4Si2-type tetragonal structure.

Table 1

Isothermal Section With starting metals of 99.9% Dy, 99.9% Fe, and 99.99% Ge, [2009Zhu] arc-melted 187 alloys under Ar atm. The alloys were given a final anneal at 500 °C for 720 h and quenched in liquid nitrogen. The phase equilibria were studied with x-ray powder diffraction, optical microscopy, and differential thermal analysis at a heating rate of 10 °C per min. The isothermal section at 500 °C constructed by [2009Zhu] is shown in Fig. 1. All the five ternary compounds listed in Table 1 are present. As seen in Fig. 1, only the Dy-Fe binary compounds show some solubility for the third component. To find whether a compound analogous to GdFe8.4Ge3.6 reported by [1996Wan] exists in this system, [2009Zhu] prepared an alloy with the composition DyFe8.4Ge3.6 and found that it consisted of two phases (a Fe) and DyFe2Ge2.

Dy-Fe-Ge crystal structure and lattice parameter data [2009Zhu]

Phase DyFe4Ge2 (s1)

DyFe6Ge6 (s2)

DyFe2Ge2 (s3)

Dy117Fe52Ge112 (s4)

DyFexGe2 or Dy5Fe2Ge10 (s5)

388

DyFe6Ge6 (s2) is orthorhombic, with Fe6Sn6Tb as the prototype. DyFe2Ge2 (s3) has the Al4Ba-type tetragonal structure. Dy117Fe52Ge112 (s4) is cubic of the Fe5Ge11Tb12-type. DyFexGe2 (s5) is CeNiSi2-type orthorhombic. It has a homogeneity range of x = 0.25-0.46, corresponding to 7.713.3 at.% Fe. Table 1 lists the structural details of these compounds. The notation s1, s2, etc., used here correspond to 1, 2, etc., used by [2009Zhu].

Composition, at.%

Pearson symbol

Space group

14.3 Dy 57.1 Fe 28.6 Ge 7.7 Dy 46.15 Fe 46.15 Ge 20 Dy 40 Fe 40 Ge 41.6 Dy 18.5 Fe 39.9 Ge 30.8-28.9 Dy 7.7-13.3 Fe 61.5-57.8 Ge

tP14

P42/mnm

ZrFe4Si2

a = 0.7318 c = 0.3865

Cmcm

Fe6Sn6Tb

I4/mmm

Al4Ba

a= b= c= a= c=

Fm3m

Fe5Ge11Tb12

a = 2.8518

Cmcm

CeNiSi2

a = 0.4121 b = 1.581 c = 0.4011

tI10

oC16

Prototype

Journal of Phase Equilibria and Diffusion Vol. 30 No. 4 2009

Lattice parameter, nm

0.8118 1.