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The isothermal section of the Dy–Fe–Ge ternary system at 773 K
Journal of Alloys and Compounds 467 (2009) 154–158
The isothermal section of the Dy–Fe–Ge ternary system at 773 K Y.H. Zhuang ∗ , C.H. Ma, K.F. Li, X. Chen Key Laboratory of Nonferrous Metal Materials and New Processing Technology, Guangxi University, Ministry of Education, Nanning, Guangxi 530004, PR China Received 24 October 2007; received in revised form 24 November 2007; accepted 27 November 2007 Available online 4 December 2007
Abstract The isothermal section of the phase diagram of the Dy–Fe–Ge ternary system at 773 K has been investigated mainly by X-ray powder diffraction (XRD), with the aid of differential thermal analysis (DTA) and optical microscopy (OM). Sixteen binary compounds have been confirmed. Five ternary compounds DyFe4 Ge2 , DyFe2 Ge2 , DyFe6 Ge6 , Dy117 Fe52 Ge112 , and Dy5 Fe2 Ge10 have been confirmed in this system at 773 K. © 2008 Published by Elsevier B.V. Keywords: Metals and alloys; Quenching; Crystal structure; X-ray diffraction
1. Introduction The magnetocaloric effect (MCE) [1–4] has been intensively studied because of its bright future in magnetic refrigeration (MR). The interest in the MCE research has grown recently. Nowadays, the search for new magnetic materials with large values of the magnetocaloric quantities is a big challenge to scientists around the world. After the discovery of the giant magnetocaloric effect (GMCE) material, scientific studies intensified on the pseudobinary Gd5 Six Ge4−x system as well as on related systems containing other lanthanides, and substituted transition metals and non-metals for Si and Ge. Recently, several tendencies regarding the preparation and characterization of the GMCE Gd5 Six Ge4−x alloys became noticeable [5–7]. As reported, the RFe6 X6 family of compounds (R = Y, Gd–Lu; X = Sn, Ge) displays magnetic behaviour which is unique among the intermetallic compounds [8–12]. Some ternary iron-rich rare earth germanides in R–Fe–Ge (R = Y, La–Er) system reveal ferromagnetic properties, such as RFe12−x Gex [13]. Wang et al. [14] found a new series of iron-rich rare earth compounds of composition RFe8.4 Ge3.6 with a high Curie temperature.
∗ Corresponding author at: Institute of Materials Science, Guangxi University, Nanning, Guangxi 530004, PR China. Tel.: +86 771 3233530; fax: +86 771 3233530. E-mail address: [email protected] (Y.H. Zhuang).
0925-8388/$ – see front matter © 2008 Published by Elsevier B.V. doi:10.1016/j.jallcom.2007.11.121
Phase diagrams can provide important information about the existence of compounds and the respective phase relations. It is the basis for improving properties and developing new materials. So the phase relationships in the Dy–Fe–Ge ternary system are well worth studying in order to provide valuable information. At present, the ternary systems R–Fe–Ge, R = Pr, Tm, Sm, Eu, Tb, Er, Yb, Ce, Nd, Ho [15] have been investigated. Up to the present, the phase diagram of the Dy–Fe–Ge ternary system has not been reported. In this paper, we studied the isothermal section of the Dy–Fe–Ge ternary system at 773 K. The phase diagrams of the binary Dy–Fe, Dy–Ge, and Fe–Ge systems were reported in [16–22], respectively. At 773 K, there are four intermetallic compounds in the Dy–Fe system, namely DyFe2 , DyFe3 , Dy6 Fe23 , and Dy2 Fe17 ; seven intermetallic compounds in the Dy–Ge system, namely Dy5 Ge3 , Dy5 Ge4 , DyGe, Dy2 Ge3 , Dy3 Ge5 , DyGe2 , and DyGe3 ; and five intermetallic compounds in the Fe–Ge system, namely Fe3 Ge, Fe5 Ge3 , Fe6 Ge5 , FeGe, and FeGe2 . Table 1 lists the data reported on the crystal structures of the compounds. 2. Experimental details Each sample was prepared with a total weight of 3 g. The purities of dysprosium, iron, and germanium used in this work are 99.9%, 99.9%, and 99.99 wt.%. One hundred and eighty-seven alloy buttons were prepared by arc melting on a water-cooled copper cast with non-consumable tungsten electrode under pure argon atmosphere with normal pressure. They were melted three times and turned around after melting for better homogeneity. Weight losses during arc melting were less than 1% of the total mass, therefore, no chemical reactions were carried out.
Y.H. Zhuang et al. / Journal of Alloys and Compounds 467 (2009) 154–158
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Table 1 The crystal structure data of intermetallic compounds in Dy–Fe, Fe–Ge, and Dy–Ge binary systems Compound
Space group
DyFe2 DyFe3 Dy6 Fe23 Dy2 Fe17 DyFe5 Dy5 Ge3 Dy5 Ge4 DyGe DyGe Dy3 Ge4 Dy2 Ge3 Dy3 Ge5 Dy6 Ge11 DyGe2 DyGe3 Fe3 Ge Fe2 Ge Fe7 Ge4 Fe3.36 Ge1.97 Fe1.67 Ge Fe5 Ge3 Fe0.615 Ge0.385 Fe3.2 Ge Fe3 Ge2 Fe13 Ge8 Fe13 Ge8 Fe6 Ge5 FeGe FeGe FeGe2 Fe90 Ge10
¯ Fd 3m(227) ¯ R3m(166) ¯ Fm3m(225) P63 /mcm(193) P6/mmm(191) P63 /mmc(194) Pnma(62) Cmcm(63) I4/mmm(139) Cmcm(63) P6/mmm(191) Fdd2(43) Cmc21 (36) Cmmm(65) Cmcm(63) ¯ Fm3m(225) P63 /mmc(194) P63 /mmc(194) P63 /mmc(194) P63 /mmc(194) P63 /mmc(194) P63 /mmc(194) P63 /mmc(194) P63 /mmc(194) P63 /mmc(194) ¯ P 3m1(164) C2/m(12) P6/mmm(191) P21 3(198) I4/mcm(140) ¯ Im3m(229)
Structure type
Lattice parameters (nm) a
Cu2 Mg Be3 Nb Mn23 Th6 Ni17 Th2 CaCu5 Mn5 Si3 Ge4 Sm5 BCr Ge10 Ho11 – AlB2 Ge5 Y3 Dy6 Ge11 Ge2 Tb DyGe3 BiF3 InNi2 AsNi InNi2 InNi2 InNi2 InNi2 Fe3 Ge2 Fe3 Ge2 Fe13 Ge8 Pd13 Tl9 Fe6 Ge5 CoSn FeSi Al2 Cu W
After casting, all samples were sealed in evacuated quartz tube for homogenization treat. The homogenization temperatures were chosen on the basis of the binary phase diagrams of the Dy–Fe, Dy–Ge, and Fe–Ge systems and the results of differential thermal analysis (DTA) of some typical ternary alloys. All the alloys were vacuum annealed at 1073 K for 500 h. Subsequently, all of the samples were cooled at a rate of 9 K/h to 773 K and kept at 773 K for 720 h, then quenched in liquid nitrogen. All homogenized alloy buttons were ground into powder, and investigated by X-ray diffraction analysis (XRD) which was carried out on a Rigaku D-MAX 2500 V diffractometer with Cu K␣ radiation and graphite monochromator operated at 40 kV and 200 mA. The Materials Data Inc. Software Jade 5.0 software [23], a Powder Diffraction File (PDF release 2004) [16], and Pearson’s Handbook of Crystallographic Data [17–19] were used to analyze the XRD data of all samples. Some typical alloys were analyzed by metallographic analysis which was performed on a Leica DMRE metallographic microscope. The DTA was done on a Netzsch STA 409PC thermal analysis meter at an increasing temperature rate of 10 K/min.
3. Results and discussion 3.1. Binary compounds In this work, we have studied the binary systems Dy–Fe, Fe–Ge, and Dy–Ge at 773 K to identify binary compounds before the ternary phase analysis. In the literature [20], it is reported that the Dy–Ge binary phase diagram was constructed, in which there are seven inter-
Reference b
0.7328 0.5125 1.210 0.8453 0.490 0.842(2) 0.7603(5) 0.4254(1) 1.081 0.4204 0.3654 0.5729(1) 4.1027(4) 0.4091(1) 0.40278(5) 0.575 0.4036 0.4027 3.994 0.4021 0.4021 0.3998 0.3998 0.3998(5) 0.7976(5) 0.796 0.9965(5) 0.50027(3) 0.4689 0.5908(3) 0.2883
– – – – – 1.4640(5) 1.0623(2) – 1.0602 – 1.7190(2) 29.705(1) 2.9807(4) 2.0710(3) 0.575 0.4036 0.4027 9.994 0.4021 0.4021 0.3998 0.3998 0.3998(5) 0.7976(5) 0.796 0.7826(5) 0.50027(3) 0.4689 0.5908(3) 0.2883
c – 2.4578 – 0.8287 0.410 0.632(1) 0.7680(5) 0.3904(1) 1.629 1.4175 0.4146 1.3678(1) 3.9316(3) 0.3987(1) 0.38997(5) 0.575 0.5030 0.5022 5.004 0.5027 0.5027 0.5010 0.501 0.5010(5) 0.4993(5) 0.499 0.780(5) 0.40548(5) 0.4689 0.4957(3) 0.2883
[19] [19] [19] [19] [19] [17] [17] [17] [17] [17] [17] [17] [17] [17] [17] [18] [18] [18] [16] [16] [16] [16] [16] [18] [18] [18] [18] [18] [18] [18] [18]
metallic compounds present: Dy5 Ge3 , Dy5 Ge4 , DyGe, Dy2 Ge3 , Dy3 Ge5 , DyGe2 , and DyGe3 . It has been confirmed in our work, by their crystal structure data which is shown in Table 1. They are in accordance with our experimental results. Ref. [21] shows that there are four compounds existing in Dy–Fe binary system: DyFe2 , DyFe3 , Dy6 Fe23 , and Dy2 Fe17 . In this work, we found that these compounds have certain solid solubilities of Ge in them. For example, the solid solubility of Ge in Dy6 Fe23 is about 2.5 at.% at 773 K. The solubilities for the other three single-phase regions have been observed too. The Fe–Ge binary system was proposed by Kato and Nunoue [22]. There are many binary compounds, particularly from 35 to 41 at.% Ge. In order to identify those phases in this region a series of alloy samples were prepared. The X-ray pattern of the alloy Fe7 Ge4 shows that the alloy is composed of Fe3 Ge and Fe5 Ge3 two phases, the phase Fe7 Ge4 is non-existent in this system. From 37 to 40 at.% Ge, there are reported compounds: Fe3.36 Ge1.97 , Fe1.67 Ge, Fe5 Ge3 , Fe13 Ge8 , Fe3.2 Ge2 , Fe0.615 Ge0.385 , and Fe3 Ge2 [16]. These compounds shared the same space group (P63/mmc(194)), and have similar lattice parameters (shown in Table 1). In this region, Salamakha et al. reported the existence of Fe3.2 Ge2 and Fe13 Ge8 in R–Fe–Ge (R = Ce, Nd, Ho) isothermal section phase diagram at 870 K [14]. Based on our data, we found that the XRD patterns of
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Y.H. Zhuang et al. / Journal of Alloys and Compounds 467 (2009) 154–158
Fig. 1. The XRD pattern of Fe5 Ge3 sample #15–20 solid solubility region. (1) #15, 37% Ge; (2) #16, 37.4% Ge; (3) #17, 37.5% Ge; (4) #18, 38.1% Ge; (5) #19, 38.5% Ge; (6) #20, 40% Ge.
these alloy samples are the same (seen in Fig. 1), as the radius ˚ > Ge = 1.52(A), ˚ and with the increasing of at.% of Fe = 1.72(A) Ge, their spectrums shift to high angle regularly. This is in accordance with the regularity of solid solubility. Thus, we concluded that these sample compounds can be replaced by one phase Fe5 Ge3 . Its solubility is about from 37 to 40 at.% Ge. It is in good agreement with Ref. [22]. Thus, only the five intermetallic compounds Fe3 Ge, Fe5 Ge3 , Fe6 Ge5 , FeGe, and FeGe2 have been confirmed in this work. This result is in good agreement with Ref. [15] except for Fe5 Ge3 . In addition, the maximum solid solubility of Ge in Fe is about 21.3 at.% at 773 K. 3.2. Ternary intermetallic compounds The main results are the identification of five ternary compounds: DyFe4 Ge2 , DyFe2 Ge2 , DyFe6 Ge6 , Dy5 Fe2 Ge10 , and Dy117 Fe52 Ge112 , which were confirmed in our ternary alloys at 773 K. Crystallographic information on the ternary compounds is summarized in Table 2. These phases were reported in the literature. The phase of DyFe4 Ge2 has been reported by SchobingerPapamantellos et al. [24,25]. In this work, we have calculated the pattern of the DyFe4 Ge2 phase using ZrFe4 Si2 -type (space group: P42 /mnm (136)), a = 0.7318(3) nm, c = 0.3865(7) nm), shows that these figures are consistent with experimental data. It means that the phase belongs to this structure. So the existence of phase DyFe4 Ge2 is confirmed in this work.
Fig. 2. (a) The isothermal section of the Dy–Fe–Ge system at 773 K. (1) DyFe4 Ge2 , (2) DyFe6 Ge6 , (3) DyFe2 Ge2 , (4) Dy117 Fe52 Ge112 , and (5) Dy5 Fe2 Ge10 . #130, #66, #149, #108, and #91 are the composition points of Figs. 4–8.
In this work, the ternary Dy5 Fe2 Ge10 phase with CeNiSi2 type structure has been confirmed [19], and a certain homogeneity range has been detected. The phase of Dy5 Fe2 Ge10 belongs to RFex Ge2 in R–Fe–Ge (R = Gd, La, Lu, Nd, etc.) ternary system. Refs. [26–28] show that this kind of phase with CeNiSi2 -type structure has certain homogeneity ranges, and has been characterized. Most of them are non-stoichiometric with wide homogeneity ranges. Their formulae are RMx X with 0 < Xmin < X < Xmax < 1. Some of them are interstitial solid solutions of M in ZrSi2 -type RX2 compounds. In order to testify to this viewpoint and measure it in the line of Dy:Ge = 2:1 (seen in Fig. 2b), from 7.692 to 14.29 Fe at.%, we prepared six alloy samples in this region. By analyzing these X-ray diffraction patterns (seen in Fig. 3), the homogeneity range in DyFex Ge2 of this compound is wide (x = 0.25–0.46). We can affirm that its homogeneity range is from 7.7 to 14.3 at.% Fe. 3.3. Isothermal section at 773 K By comparing and analyzing the X-ray diffraction patterns, microstructures and DTA data, the 773 K isothermal section of the phase diagram of Dy–Fe–Ge system was constituted. It can
Table 2 The data on the crystal structures of the compounds of the Dy–Fe–Ge ternary system Compound
DyFe2 Ge2 DyFe6 Ge6 DyFe6 Ge6 Dy5 Fe2 Ge10 DyFex Ge2 Dy117 Fe52 Ge112 DyFe4 Ge2
Space group
I4/mmm(139) P6/mmm(191) Cmcm(63) Cmcm(63) – ¯ Fm3m(225) P42 /mnm(136)
Structure type
Al4 Ba Cu7 Tb Fe6 Sn6 Tb CeNiSi2 CeNiSi2 Fe5 Ge11 Tb12 ZrFe4 Si2
Lattice parameters (nm)
Reference
a
b
c
0.3957 0.5108(2) 0.8118(2) 0.4121(3) – 2.8518 0.7318(3)
– – 1.768(1) 1.581(1) – 2.8518 –
1.0446 0.4044(3) 0.5116(2) 0.4011(4) – 2.8518 0.3865(7)
[19] [19] [19] [19] [27] [17] This work
Y.H. Zhuang et al. / Journal of Alloys and Compounds 467 (2009) 154–158
Fig. 3. The XRD pattern of sample DyFex Ge2 solid solubility region. (1) #164, 57.1% Ge; (2) #163, 58% Ge; (3) #162, 58.8% Ge; (4) #76, 60.1% Ge; (5) #161, 60.8% Ge; (6) #160, 61.5% Ge.
Fig. 4. The XRD pattern of #130 sample (Dy-28 at.% + Fe-22 at.% + Ge50 at.%): DyGe + Dy5 Fe2 Ge10 + DyFe2 Ge2 .
be seen in Fig. 2a. The existence of 16 binary compounds and five ternary compounds are shown in Tables 1 and 2, respectively. The XRD patterns of these phases can be found in the XRD patterns of the samples located in the three-phase regions. DyGe + Dy5 Fe2 Ge10 + DyFe2 Ge2 (#130 sample, Dy: 28 at.%, Fe: 22 at.%, Ge: 50 at.%) is shown in Fig. 4. The XRD pat-
Fig. 5. The XRD pattern of #66 sample (Dy-14 at.% + Fe-20 at.% + Ge-66 at.%): Dy5 Fe2 Ge10 + DyFe6 Ge6 + Ge.
157
Fig. 6. The XRD pattern of #149 sample (Dy-2.5 at.% + Fe-56 at.% + Ge41.5 at.%): DyFe6 Ge6 + Fe5 Ge3 .
Fig. 7. The XRD pattern of #108 sample (Dy-10.5 at.% + Fe-64.8 at.% + Ge24.7 at.%): DyFe4 Ge2 + DyFe2 Ge2 + Fe.
tern of sample #66 (Dy: 14 at.% + Fe: 20 at.% + Ge: 66 at.%) is shown in Fig. 5. It can be seen that the sample consists of Dy5 Fe2 Ge10 , DyFe6 Ge6 and Ge. Fig. 6 is the XRD pattern of sample #149 (Dy: 2.5 at.%, Fe: 56 at.%, Ge: 41.5 at.%). It clearly shows that it is a two-phase region and constituted of DyFe6 Ge6 and Fe5 Ge3 . Fig. 7 is the XRD pattern of #108 sample (Dy: 10.5 at.%, Fe: 64.8 at.%, Ge: 24.7 at.%). It can be seen
Fig. 8. The XRD pattern of #91 sample (Dy-7.7 at.% + Fe-64.6 at.% + Ge27.7 at.%: the pattern of DyFe8.4 Ge3.6 is composed of two phases): DyFe2 Ge2 + Fe.
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Table 3 The phase constituent of the three-phase regions in the isothermal section of phase diagram of Dy–Fe–Ge ternary system at 773 K Phase region
Phase composition
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
DyFe2 + Dy5 Ge3 + Dy Dy5 Ge3 + DyFe2 + DyFe3 Dy5 Ge3 + DyFe3 + Dy6 Fe23 Dy5 Ge3 + Dy6 Fe23 + Dy2 Fe17 Dy5 Ge3 + Dy2 Fe17 + Fe Dy5 Ge3 + Dy117 Fe52 Ge112 + Fe DyFe4 Ge2 + Dy117 Fe52 Ge112 + Fe DyFe4 Ge2 + DyFe2 Ge2 + Fe DyFe2 Ge2 + Fe3 Ge + Fe DyFe4 Ge2 + Dy117 Fe52 Ge112 + DyFe2 Ge2 DyFe2 Ge2 + Fe5 Ge3 + Fe3 Ge DyFe6 Ge6 + Fe5 Ge3 + DyFe2 Ge2 DyFe6 Ge6 + Fe5 Ge3 + Fe6 Ge5 DyFe6 Ge6 + Fe6 Ge5 + FeGe DyFe6 Ge6 + FeGe + FeGe2 DyFe6 Ge6 + FeGe2 + Ge DyFe6 Ge6 + Dy5 Fe2 Ge10 + Ge DyFe6 Ge6 + Dy5 Fe2 Ge10 + DyFe2 Ge2 DyFe2 Ge2 + Dy5 Fe2 Ge10 + DyGe DyFe2 Ge2 + Dy117 Fe52 Ge112 + DyGe Dy117 Fe52 Ge112 + Dy5 Ge3 + Dy5 Ge4 Dy5 Ge4 + Dy117 Fe52 Ge112 + DyGe Dy5 Fe2 Ge10 + Dy2 Ge3 + DyGe Dy5 Fe2 Ge10 + Dy3 Ge5 + Dy2 Ge3 Dy5 Fe2 Ge10 + Dy3 Ge5 + DyGe2 Dy5 Fe2 Ge10 + DyGe2 + DyGe3 Dy5 Fe2 Ge10 + DyGe3 + Ge
that the sample consists of DyFe4 Ge2 , DyFe2 Ge2 , and Fe5 Ge3 . GdFe8.4 Ge3.6 compound was reported by Wang et al. [14]. In our work, the XRD pattern of the DyFe8.4 Ge3.6 compound clearly shows that they are constituted of two different phases (shown in Fig. 8): the ␣-Fe(Ge) solid solution and the DyFe2 Ge2 . Our other work about Gd–Fe–Ge system [29] has also confirmed this point of view. This isothermal section consists of 24 single-phase regions, 51 two-phase regions, and 27 three-phase regions. Details of the three-phase regions are given in Table 3. 4. Conclusions The results show that a certain amount of Fe atoms can be replaced by Ge. At 773 K, many solid solution regions were observed in the Dy–Fe–Ge ternary system. This work has observed Fe5 Ge3 with its solubility from 37 to 40 at.% Ge. The maximum solid solubility of Ge in Fe is about 21.3 at.%. The homogeneity range of DyFex Ge2 phase is 7.7–14.3 at.% Fe. The isothermal section of the phase diagram of the Dy–Fe–Ge ternary system at 773 K has been determined. Five ternary compounds have been confirmed in this system at 773 K. The isothermal section consists of 24 single-phase regions, 51 twophase regions, and 27 three-phase regions.
Acknowledgement This work was supported by the National Natural Science Foundation of China (Grant No. 50371058). References [1] A.M. Tishin, Handbook of Magnetic Materials, vol. 12, North-Holland, Amsterdam, 1999, pp. 395–524. [2] K.A. Gschneidner Jr., V.K. Pecharsky, A.O. Tsokol, Rep. Prog. Phys. 68 (2005) 1479–1539. [3] L.G. de Medeiros Jr., N.A. de Oliveira, J. Magn. Magn. Mater. 306 (2006) 265–271. [4] A.M. Tishin, A.V. Derkach, Y.I. Spichkin, M.D. Kuz’min, A.S. Chernyshov, K.A. Gschneidner Jr., V.K. Pecharsky, J. Magn. Magn. Mater. 310 (2007) 2800–2804. [5] W. Wu, A.O. Tsokol, K.A. Gschneidner Jr., J.A. Sampaio, J. Alloys Compd. 403 (2005) 118–123. [6] Y.H. Zhuang, W.D. Huang, J.Q. Li, Y.X. Jian, J.L. Huang, J. Alloys Compd. 414 (2006) 78–81. [7] V.K. Pecharsky, K.A. Gschneidner Jr., J. Magn. Magn. Mater. 167 (1997) L179–L184. [8] J.M. Cadogan, D.H. Ryan, J. Alloys Compd. 326 (2001) 166–173. [9] G. Venturini, R. Welter, B. Malaman, J. Alloys Compd. 185 (1992) 99–107. [10] B. Chafik El Idrissi, G. Venturini, B. Malaman, Mater. Res. Bull. 26 (12) (1991) 1331–1338. [11] G. Venturini, J. Alloys Compd. 400 (2005) 37–42. [12] L.K. Perry, D.H. Ryan, G. Venturini, B. Malaman, J. Alloys Compd. 436 (2007) 1–8. [13] V. Lachevre, B. Barbara, D. Fruchart, L. Pontonnier, J. Alloys Compd. 275 (1998) 615–619. [14] K.Y. Wang, J. Hu, Y.Z. Wang, B.P. Hu, Z.X. Wang, J. Alloys Compd. 233 (1996) L1–L2. [15] R. Salamakha, M. Konyk, O. Sologub, O. Bodak, J. Alloys Compd. 234 (1996) 151–156. [16] Powder Diffraction File, International Center for Diffraction Data, 2004. [17] P. Villars, Pearson’s Handbook of Crystallographic Data, ASM International, Materials Park, OH, 1997, pp. 1615–1617. [18] P. Villars, Pearson’s Handbook of Crystallographic Data, ASM International, Materials Park, OH, 1997, pp. 1727–1729. [19] P. Villars, Pearson’s Handbook of Crystallographic Data, ASM International, Materials Park, OH, 1997, pp. 1606–1607. [20] V.N. Eremenko, V.G. Batalin, Yu.I. Buyanov, I.M. Obushenko, Dop. Akad. Nauk Ukr. RSR B (6) (1977) 516–521 (in Russian). [21] H. Okamoto, in: H. Okamoto (Ed.), Phase Diagrams of Binary Iron Alloys, ASM International, Materials Park, OH, 1993, pp. 341–349. [22] E. Kato, S. Nunoue, Binary Alloy Phase Diagrams, vol. 2, 2nd ed., The Materials Information Society, Materials Park, OH, 1990, pp. 1705– 1707. [23] Materials Data JADE Release 5, XRD Pattern Processing, Materials Data Inc. (MDI), 2002. [24] P. Schobinger-Papamantellos, J. Rodriguez-Carvajal, K.H.J. Buschow, E. Dooryhee, A.N. Fitch, J. Magn. Magn. Mater. 300 (2006) 315–332. [25] P. Schobinger-Papamantellos, J. Rodriguez-Carvajal, G. Andre, K.H.J. Buschow, J. Magn. Magn. Mater. 300 (2006) 333–350. [26] P. Villars, Pearson’s Handbook of Crystallographic Data, ASM International, Materials Park, OH, 1997, pp. 1724–1732. [27] M. Francois, G. Venturini, B. Malaman, B. Roques, J. Less-Common Met. 160 (1990) 197–213. [28] J. St˛epien-Damm, O.I. Bodak, B.D. Belan, E. Galc¸decka, J. Alloys Compd. 298 (2000) 169–172. [29] Y.H. Zhuang, K.F. Li, C.H. Ma, X. Chen, J. Alloys Compd 467 (2009) 251–256.
The isothermal section of the Dy–Fe–Ge ternary system at 773 K Y.H. Zhuang ∗ , C.H. Ma, K.F. Li, X. Chen Key Laboratory of Nonferrous Metal Materials and New Processing Technology, Guangxi University, Ministry of Education, Nanning, Guangxi 530004, PR China Received 24 October 2007; received in revised form 24 November 2007; accepted 27 November 2007 Available online 4 December 2007
Abstract The isothermal section of the phase diagram of the Dy–Fe–Ge ternary system at 773 K has been investigated mainly by X-ray powder diffraction (XRD), with the aid of differential thermal analysis (DTA) and optical microscopy (OM). Sixteen binary compounds have been confirmed. Five ternary compounds DyFe4 Ge2 , DyFe2 Ge2 , DyFe6 Ge6 , Dy117 Fe52 Ge112 , and Dy5 Fe2 Ge10 have been confirmed in this system at 773 K. © 2008 Published by Elsevier B.V. Keywords: Metals and alloys; Quenching; Crystal structure; X-ray diffraction
1. Introduction The magnetocaloric effect (MCE) [1–4] has been intensively studied because of its bright future in magnetic refrigeration (MR). The interest in the MCE research has grown recently. Nowadays, the search for new magnetic materials with large values of the magnetocaloric quantities is a big challenge to scientists around the world. After the discovery of the giant magnetocaloric effect (GMCE) material, scientific studies intensified on the pseudobinary Gd5 Six Ge4−x system as well as on related systems containing other lanthanides, and substituted transition metals and non-metals for Si and Ge. Recently, several tendencies regarding the preparation and characterization of the GMCE Gd5 Six Ge4−x alloys became noticeable [5–7]. As reported, the RFe6 X6 family of compounds (R = Y, Gd–Lu; X = Sn, Ge) displays magnetic behaviour which is unique among the intermetallic compounds [8–12]. Some ternary iron-rich rare earth germanides in R–Fe–Ge (R = Y, La–Er) system reveal ferromagnetic properties, such as RFe12−x Gex [13]. Wang et al. [14] found a new series of iron-rich rare earth compounds of composition RFe8.4 Ge3.6 with a high Curie temperature.
∗ Corresponding author at: Institute of Materials Science, Guangxi University, Nanning, Guangxi 530004, PR China. Tel.: +86 771 3233530; fax: +86 771 3233530. E-mail address: [email protected] (Y.H. Zhuang).
0925-8388/$ – see front matter © 2008 Published by Elsevier B.V. doi:10.1016/j.jallcom.2007.11.121
Phase diagrams can provide important information about the existence of compounds and the respective phase relations. It is the basis for improving properties and developing new materials. So the phase relationships in the Dy–Fe–Ge ternary system are well worth studying in order to provide valuable information. At present, the ternary systems R–Fe–Ge, R = Pr, Tm, Sm, Eu, Tb, Er, Yb, Ce, Nd, Ho [15] have been investigated. Up to the present, the phase diagram of the Dy–Fe–Ge ternary system has not been reported. In this paper, we studied the isothermal section of the Dy–Fe–Ge ternary system at 773 K. The phase diagrams of the binary Dy–Fe, Dy–Ge, and Fe–Ge systems were reported in [16–22], respectively. At 773 K, there are four intermetallic compounds in the Dy–Fe system, namely DyFe2 , DyFe3 , Dy6 Fe23 , and Dy2 Fe17 ; seven intermetallic compounds in the Dy–Ge system, namely Dy5 Ge3 , Dy5 Ge4 , DyGe, Dy2 Ge3 , Dy3 Ge5 , DyGe2 , and DyGe3 ; and five intermetallic compounds in the Fe–Ge system, namely Fe3 Ge, Fe5 Ge3 , Fe6 Ge5 , FeGe, and FeGe2 . Table 1 lists the data reported on the crystal structures of the compounds. 2. Experimental details Each sample was prepared with a total weight of 3 g. The purities of dysprosium, iron, and germanium used in this work are 99.9%, 99.9%, and 99.99 wt.%. One hundred and eighty-seven alloy buttons were prepared by arc melting on a water-cooled copper cast with non-consumable tungsten electrode under pure argon atmosphere with normal pressure. They were melted three times and turned around after melting for better homogeneity. Weight losses during arc melting were less than 1% of the total mass, therefore, no chemical reactions were carried out.
Y.H. Zhuang et al. / Journal of Alloys and Compounds 467 (2009) 154–158
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Table 1 The crystal structure data of intermetallic compounds in Dy–Fe, Fe–Ge, and Dy–Ge binary systems Compound
Space group
DyFe2 DyFe3 Dy6 Fe23 Dy2 Fe17 DyFe5 Dy5 Ge3 Dy5 Ge4 DyGe DyGe Dy3 Ge4 Dy2 Ge3 Dy3 Ge5 Dy6 Ge11 DyGe2 DyGe3 Fe3 Ge Fe2 Ge Fe7 Ge4 Fe3.36 Ge1.97 Fe1.67 Ge Fe5 Ge3 Fe0.615 Ge0.385 Fe3.2 Ge Fe3 Ge2 Fe13 Ge8 Fe13 Ge8 Fe6 Ge5 FeGe FeGe FeGe2 Fe90 Ge10
¯ Fd 3m(227) ¯ R3m(166) ¯ Fm3m(225) P63 /mcm(193) P6/mmm(191) P63 /mmc(194) Pnma(62) Cmcm(63) I4/mmm(139) Cmcm(63) P6/mmm(191) Fdd2(43) Cmc21 (36) Cmmm(65) Cmcm(63) ¯ Fm3m(225) P63 /mmc(194) P63 /mmc(194) P63 /mmc(194) P63 /mmc(194) P63 /mmc(194) P63 /mmc(194) P63 /mmc(194) P63 /mmc(194) P63 /mmc(194) ¯ P 3m1(164) C2/m(12) P6/mmm(191) P21 3(198) I4/mcm(140) ¯ Im3m(229)
Structure type
Lattice parameters (nm) a
Cu2 Mg Be3 Nb Mn23 Th6 Ni17 Th2 CaCu5 Mn5 Si3 Ge4 Sm5 BCr Ge10 Ho11 – AlB2 Ge5 Y3 Dy6 Ge11 Ge2 Tb DyGe3 BiF3 InNi2 AsNi InNi2 InNi2 InNi2 InNi2 Fe3 Ge2 Fe3 Ge2 Fe13 Ge8 Pd13 Tl9 Fe6 Ge5 CoSn FeSi Al2 Cu W
After casting, all samples were sealed in evacuated quartz tube for homogenization treat. The homogenization temperatures were chosen on the basis of the binary phase diagrams of the Dy–Fe, Dy–Ge, and Fe–Ge systems and the results of differential thermal analysis (DTA) of some typical ternary alloys. All the alloys were vacuum annealed at 1073 K for 500 h. Subsequently, all of the samples were cooled at a rate of 9 K/h to 773 K and kept at 773 K for 720 h, then quenched in liquid nitrogen. All homogenized alloy buttons were ground into powder, and investigated by X-ray diffraction analysis (XRD) which was carried out on a Rigaku D-MAX 2500 V diffractometer with Cu K␣ radiation and graphite monochromator operated at 40 kV and 200 mA. The Materials Data Inc. Software Jade 5.0 software [23], a Powder Diffraction File (PDF release 2004) [16], and Pearson’s Handbook of Crystallographic Data [17–19] were used to analyze the XRD data of all samples. Some typical alloys were analyzed by metallographic analysis which was performed on a Leica DMRE metallographic microscope. The DTA was done on a Netzsch STA 409PC thermal analysis meter at an increasing temperature rate of 10 K/min.
3. Results and discussion 3.1. Binary compounds In this work, we have studied the binary systems Dy–Fe, Fe–Ge, and Dy–Ge at 773 K to identify binary compounds before the ternary phase analysis. In the literature [20], it is reported that the Dy–Ge binary phase diagram was constructed, in which there are seven inter-
Reference b
0.7328 0.5125 1.210 0.8453 0.490 0.842(2) 0.7603(5) 0.4254(1) 1.081 0.4204 0.3654 0.5729(1) 4.1027(4) 0.4091(1) 0.40278(5) 0.575 0.4036 0.4027 3.994 0.4021 0.4021 0.3998 0.3998 0.3998(5) 0.7976(5) 0.796 0.9965(5) 0.50027(3) 0.4689 0.5908(3) 0.2883
– – – – – 1.4640(5) 1.0623(2) – 1.0602 – 1.7190(2) 29.705(1) 2.9807(4) 2.0710(3) 0.575 0.4036 0.4027 9.994 0.4021 0.4021 0.3998 0.3998 0.3998(5) 0.7976(5) 0.796 0.7826(5) 0.50027(3) 0.4689 0.5908(3) 0.2883
c – 2.4578 – 0.8287 0.410 0.632(1) 0.7680(5) 0.3904(1) 1.629 1.4175 0.4146 1.3678(1) 3.9316(3) 0.3987(1) 0.38997(5) 0.575 0.5030 0.5022 5.004 0.5027 0.5027 0.5010 0.501 0.5010(5) 0.4993(5) 0.499 0.780(5) 0.40548(5) 0.4689 0.4957(3) 0.2883
[19] [19] [19] [19] [19] [17] [17] [17] [17] [17] [17] [17] [17] [17] [17] [18] [18] [18] [16] [16] [16] [16] [16] [18] [18] [18] [18] [18] [18] [18] [18]
metallic compounds present: Dy5 Ge3 , Dy5 Ge4 , DyGe, Dy2 Ge3 , Dy3 Ge5 , DyGe2 , and DyGe3 . It has been confirmed in our work, by their crystal structure data which is shown in Table 1. They are in accordance with our experimental results. Ref. [21] shows that there are four compounds existing in Dy–Fe binary system: DyFe2 , DyFe3 , Dy6 Fe23 , and Dy2 Fe17 . In this work, we found that these compounds have certain solid solubilities of Ge in them. For example, the solid solubility of Ge in Dy6 Fe23 is about 2.5 at.% at 773 K. The solubilities for the other three single-phase regions have been observed too. The Fe–Ge binary system was proposed by Kato and Nunoue [22]. There are many binary compounds, particularly from 35 to 41 at.% Ge. In order to identify those phases in this region a series of alloy samples were prepared. The X-ray pattern of the alloy Fe7 Ge4 shows that the alloy is composed of Fe3 Ge and Fe5 Ge3 two phases, the phase Fe7 Ge4 is non-existent in this system. From 37 to 40 at.% Ge, there are reported compounds: Fe3.36 Ge1.97 , Fe1.67 Ge, Fe5 Ge3 , Fe13 Ge8 , Fe3.2 Ge2 , Fe0.615 Ge0.385 , and Fe3 Ge2 [16]. These compounds shared the same space group (P63/mmc(194)), and have similar lattice parameters (shown in Table 1). In this region, Salamakha et al. reported the existence of Fe3.2 Ge2 and Fe13 Ge8 in R–Fe–Ge (R = Ce, Nd, Ho) isothermal section phase diagram at 870 K [14]. Based on our data, we found that the XRD patterns of
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Fig. 1. The XRD pattern of Fe5 Ge3 sample #15–20 solid solubility region. (1) #15, 37% Ge; (2) #16, 37.4% Ge; (3) #17, 37.5% Ge; (4) #18, 38.1% Ge; (5) #19, 38.5% Ge; (6) #20, 40% Ge.
these alloy samples are the same (seen in Fig. 1), as the radius ˚ > Ge = 1.52(A), ˚ and with the increasing of at.% of Fe = 1.72(A) Ge, their spectrums shift to high angle regularly. This is in accordance with the regularity of solid solubility. Thus, we concluded that these sample compounds can be replaced by one phase Fe5 Ge3 . Its solubility is about from 37 to 40 at.% Ge. It is in good agreement with Ref. [22]. Thus, only the five intermetallic compounds Fe3 Ge, Fe5 Ge3 , Fe6 Ge5 , FeGe, and FeGe2 have been confirmed in this work. This result is in good agreement with Ref. [15] except for Fe5 Ge3 . In addition, the maximum solid solubility of Ge in Fe is about 21.3 at.% at 773 K. 3.2. Ternary intermetallic compounds The main results are the identification of five ternary compounds: DyFe4 Ge2 , DyFe2 Ge2 , DyFe6 Ge6 , Dy5 Fe2 Ge10 , and Dy117 Fe52 Ge112 , which were confirmed in our ternary alloys at 773 K. Crystallographic information on the ternary compounds is summarized in Table 2. These phases were reported in the literature. The phase of DyFe4 Ge2 has been reported by SchobingerPapamantellos et al. [24,25]. In this work, we have calculated the pattern of the DyFe4 Ge2 phase using ZrFe4 Si2 -type (space group: P42 /mnm (136)), a = 0.7318(3) nm, c = 0.3865(7) nm), shows that these figures are consistent with experimental data. It means that the phase belongs to this structure. So the existence of phase DyFe4 Ge2 is confirmed in this work.
Fig. 2. (a) The isothermal section of the Dy–Fe–Ge system at 773 K. (1) DyFe4 Ge2 , (2) DyFe6 Ge6 , (3) DyFe2 Ge2 , (4) Dy117 Fe52 Ge112 , and (5) Dy5 Fe2 Ge10 . #130, #66, #149, #108, and #91 are the composition points of Figs. 4–8.
In this work, the ternary Dy5 Fe2 Ge10 phase with CeNiSi2 type structure has been confirmed [19], and a certain homogeneity range has been detected. The phase of Dy5 Fe2 Ge10 belongs to RFex Ge2 in R–Fe–Ge (R = Gd, La, Lu, Nd, etc.) ternary system. Refs. [26–28] show that this kind of phase with CeNiSi2 -type structure has certain homogeneity ranges, and has been characterized. Most of them are non-stoichiometric with wide homogeneity ranges. Their formulae are RMx X with 0 < Xmin < X < Xmax < 1. Some of them are interstitial solid solutions of M in ZrSi2 -type RX2 compounds. In order to testify to this viewpoint and measure it in the line of Dy:Ge = 2:1 (seen in Fig. 2b), from 7.692 to 14.29 Fe at.%, we prepared six alloy samples in this region. By analyzing these X-ray diffraction patterns (seen in Fig. 3), the homogeneity range in DyFex Ge2 of this compound is wide (x = 0.25–0.46). We can affirm that its homogeneity range is from 7.7 to 14.3 at.% Fe. 3.3. Isothermal section at 773 K By comparing and analyzing the X-ray diffraction patterns, microstructures and DTA data, the 773 K isothermal section of the phase diagram of Dy–Fe–Ge system was constituted. It can
Table 2 The data on the crystal structures of the compounds of the Dy–Fe–Ge ternary system Compound
DyFe2 Ge2 DyFe6 Ge6 DyFe6 Ge6 Dy5 Fe2 Ge10 DyFex Ge2 Dy117 Fe52 Ge112 DyFe4 Ge2
Space group
I4/mmm(139) P6/mmm(191) Cmcm(63) Cmcm(63) – ¯ Fm3m(225) P42 /mnm(136)
Structure type
Al4 Ba Cu7 Tb Fe6 Sn6 Tb CeNiSi2 CeNiSi2 Fe5 Ge11 Tb12 ZrFe4 Si2
Lattice parameters (nm)
Reference
a
b
c
0.3957 0.5108(2) 0.8118(2) 0.4121(3) – 2.8518 0.7318(3)
– – 1.768(1) 1.581(1) – 2.8518 –
1.0446 0.4044(3) 0.5116(2) 0.4011(4) – 2.8518 0.3865(7)
[19] [19] [19] [19] [27] [17] This work
Y.H. Zhuang et al. / Journal of Alloys and Compounds 467 (2009) 154–158
Fig. 3. The XRD pattern of sample DyFex Ge2 solid solubility region. (1) #164, 57.1% Ge; (2) #163, 58% Ge; (3) #162, 58.8% Ge; (4) #76, 60.1% Ge; (5) #161, 60.8% Ge; (6) #160, 61.5% Ge.
Fig. 4. The XRD pattern of #130 sample (Dy-28 at.% + Fe-22 at.% + Ge50 at.%): DyGe + Dy5 Fe2 Ge10 + DyFe2 Ge2 .
be seen in Fig. 2a. The existence of 16 binary compounds and five ternary compounds are shown in Tables 1 and 2, respectively. The XRD patterns of these phases can be found in the XRD patterns of the samples located in the three-phase regions. DyGe + Dy5 Fe2 Ge10 + DyFe2 Ge2 (#130 sample, Dy: 28 at.%, Fe: 22 at.%, Ge: 50 at.%) is shown in Fig. 4. The XRD pat-
Fig. 5. The XRD pattern of #66 sample (Dy-14 at.% + Fe-20 at.% + Ge-66 at.%): Dy5 Fe2 Ge10 + DyFe6 Ge6 + Ge.
157
Fig. 6. The XRD pattern of #149 sample (Dy-2.5 at.% + Fe-56 at.% + Ge41.5 at.%): DyFe6 Ge6 + Fe5 Ge3 .
Fig. 7. The XRD pattern of #108 sample (Dy-10.5 at.% + Fe-64.8 at.% + Ge24.7 at.%): DyFe4 Ge2 + DyFe2 Ge2 + Fe.
tern of sample #66 (Dy: 14 at.% + Fe: 20 at.% + Ge: 66 at.%) is shown in Fig. 5. It can be seen that the sample consists of Dy5 Fe2 Ge10 , DyFe6 Ge6 and Ge. Fig. 6 is the XRD pattern of sample #149 (Dy: 2.5 at.%, Fe: 56 at.%, Ge: 41.5 at.%). It clearly shows that it is a two-phase region and constituted of DyFe6 Ge6 and Fe5 Ge3 . Fig. 7 is the XRD pattern of #108 sample (Dy: 10.5 at.%, Fe: 64.8 at.%, Ge: 24.7 at.%). It can be seen
Fig. 8. The XRD pattern of #91 sample (Dy-7.7 at.% + Fe-64.6 at.% + Ge27.7 at.%: the pattern of DyFe8.4 Ge3.6 is composed of two phases): DyFe2 Ge2 + Fe.
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Table 3 The phase constituent of the three-phase regions in the isothermal section of phase diagram of Dy–Fe–Ge ternary system at 773 K Phase region
Phase composition
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
DyFe2 + Dy5 Ge3 + Dy Dy5 Ge3 + DyFe2 + DyFe3 Dy5 Ge3 + DyFe3 + Dy6 Fe23 Dy5 Ge3 + Dy6 Fe23 + Dy2 Fe17 Dy5 Ge3 + Dy2 Fe17 + Fe Dy5 Ge3 + Dy117 Fe52 Ge112 + Fe DyFe4 Ge2 + Dy117 Fe52 Ge112 + Fe DyFe4 Ge2 + DyFe2 Ge2 + Fe DyFe2 Ge2 + Fe3 Ge + Fe DyFe4 Ge2 + Dy117 Fe52 Ge112 + DyFe2 Ge2 DyFe2 Ge2 + Fe5 Ge3 + Fe3 Ge DyFe6 Ge6 + Fe5 Ge3 + DyFe2 Ge2 DyFe6 Ge6 + Fe5 Ge3 + Fe6 Ge5 DyFe6 Ge6 + Fe6 Ge5 + FeGe DyFe6 Ge6 + FeGe + FeGe2 DyFe6 Ge6 + FeGe2 + Ge DyFe6 Ge6 + Dy5 Fe2 Ge10 + Ge DyFe6 Ge6 + Dy5 Fe2 Ge10 + DyFe2 Ge2 DyFe2 Ge2 + Dy5 Fe2 Ge10 + DyGe DyFe2 Ge2 + Dy117 Fe52 Ge112 + DyGe Dy117 Fe52 Ge112 + Dy5 Ge3 + Dy5 Ge4 Dy5 Ge4 + Dy117 Fe52 Ge112 + DyGe Dy5 Fe2 Ge10 + Dy2 Ge3 + DyGe Dy5 Fe2 Ge10 + Dy3 Ge5 + Dy2 Ge3 Dy5 Fe2 Ge10 + Dy3 Ge5 + DyGe2 Dy5 Fe2 Ge10 + DyGe2 + DyGe3 Dy5 Fe2 Ge10 + DyGe3 + Ge
that the sample consists of DyFe4 Ge2 , DyFe2 Ge2 , and Fe5 Ge3 . GdFe8.4 Ge3.6 compound was reported by Wang et al. [14]. In our work, the XRD pattern of the DyFe8.4 Ge3.6 compound clearly shows that they are constituted of two different phases (shown in Fig. 8): the ␣-Fe(Ge) solid solution and the DyFe2 Ge2 . Our other work about Gd–Fe–Ge system [29] has also confirmed this point of view. This isothermal section consists of 24 single-phase regions, 51 two-phase regions, and 27 three-phase regions. Details of the three-phase regions are given in Table 3. 4. Conclusions The results show that a certain amount of Fe atoms can be replaced by Ge. At 773 K, many solid solution regions were observed in the Dy–Fe–Ge ternary system. This work has observed Fe5 Ge3 with its solubility from 37 to 40 at.% Ge. The maximum solid solubility of Ge in Fe is about 21.3 at.%. The homogeneity range of DyFex Ge2 phase is 7.7–14.3 at.% Fe. The isothermal section of the phase diagram of the Dy–Fe–Ge ternary system at 773 K has been determined. Five ternary compounds have been confirmed in this system at 773 K. The isothermal section consists of 24 single-phase regions, 51 twophase regions, and 27 three-phase regions.
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