Phase relations in the NdCoSi system at 800°C

Phase relations in the NdCoSi system at 800°C

Jew, •• 1 .f AI.J..OYS AND COMIPOUNDS ELSEVIER Journal of Alloys and Compounds 241 (1996) 191-195 Phase relations in the Nd-Co-Si system at 800°C Y...

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Jew, •• 1 .f

AI.J..OYS AND COMIPOUNDS ELSEVIER

Journal of Alloys and Compounds 241 (1996) 191-195

Phase relations in the Nd-Co-Si system at 800°C Yanming Zhao", Jingkui Liang":", Guanghui Rao", Yongquan Guo", Weihua Tang", Cheng Dong", Fei WU c , 'Institute of Physics. Chinese Academy of Sciences. p.o. Box 603. Beijing 100080. People's Republic of China "lnternational Center for Materials Physics. Chinese Academy of Sciences. Shengyang 11()()15. People's Republic of China
Received 27 November 1995; in final form 24 January 1996

Abstract Phase equilibria in the ternary Nd-Cs-Si system up to a Co:Nd atomic ratio of 2:1 and an Si:Nd atomic ratio of 3:5 were studied by means of X-ray powder diffraction. A total of seven ternary compounds were identified. Among the seven ternary compounds found in this system, the solid solubility of two compounds had not been reported previously: NdC0 t3 _ .. Si.. with 2.5 ~x ~ 4 and NdColl_ x Six with 1.2 ~x ~ 1.8. Other new information includes the crysta! structure of NdCo 13 _ .. Si... It has a tetragonal structure, related to the NaZn 13-type, with a = 7.811-7.763 A, c = 11.430-11.464 A, and the atomic ordering is similar to Ce 2Ni 17Si 9 • A limited solid solution range has also been found for Nd 2Co 17 _ x Si... This isothermal section consists of 26 three-phase and four two-phase regions. Keywords: Intermetallic compounds: Rare earth compounds; Nd-Co-Si system; Phase relations; Ternary section

1. Introduction Among rare earth-transition metal intermetallic compounds, LaCo 13 is known to have the highest concentration of transition element, and thus a very large magnetization (13 kG at room temperature) and high Curie temperature (Tc = 1318K) [1]. However, the possibility of using LaCo 13 as a 'permanent magnetic material is low, because the crystal structure of LaCOn is highly symmetric (cubic NaZn 13-type) and lacks significant magnetocrystalline anisotropy. Among R-T intermetallic compounds (R = rare earth, T = transition metal) [2] only LaCo 13 forms a stable 1-13 cubic structure. Thus it is interesting to lower the symmetry and possibly generate anisotropy. The LaCo 13-type structure is not stable for R-elements other than La. Furthermore, neither LaFe 13 nor LaNi 13 exist, even though they can be stabilized by adding non-magnetic elements such as Si and Al [3,4]. Several researchers have tried to improve the magnetocrystalline anisotropy of LaCo 13-based intermetallie compounds by elemental substitution [1] and nitrogenation [5], but were not able to lower the crystal symmetry. Much research in this direction has been performed recently, due to a possible application as Copyright <0 1996 Published by Elsevier Science S.A. All rights reserved Pl/: S0925-8388(96 )02249-9

permanent magnets. The existence of NdCo lO,sSi 2.s with ~he cubic NaZn 13-type structure (Fm3c, a = 11.24A) was reported by Kripyakevich et al. [6] from X-ray powder diffraction data of arc-melted alloys. An extended solid solubility of Si in NdCo 13 _ .. Six was not reported. However, our experimental results show that there exists NdCo 13_ xSix (2.5:eo; x :eo; 4) with a tetragonal NaZn 13-derivative type structure. To our knowledge, no phase diagram of the Nd-Co-Si system is available yet. Thus, reliable information on the phase equilibria in the Nd-Co-Si system is desirable for a systematic investigation of the extent of the homogeneity range of the tetragonal NaZn 13-type phase NdCo 13 _ xSix with space group /4/mcm. In this paper an isothermal section of Nd-Co-Si ternary diagram is described and new data for some of the compounds are given.

2. Experimental details All alloy samples (123 in total) with a mass of 3 g for each sample were prepared by arc-melting the appropriate amounts of starting materials in an atmosphere of ultrapure argon gas. The purity of the three

192

Y. Zhao et al. I Journal of Alloys and Compounds 241 (1996) 191-195

starting elements was higher than 99.9%. Excesses of 2% Nd were added to compensate for mass loss due to the evaporation of the rare earth elements during melting. The samples were remelted several times to ensure full mixing. The weight losses during melting were less than 2 wt.% for a total 123 specimens. The samples obtained were sealed in quartz capsules that were evacuated to lO- z Torr and annealed at 800 °C for two months. The annealing temperature was controlled within ±5 "C, The phase identification of the samples was carried out by X-ray powder diffraction, using a four-layer monochromatic focusing Guinier-de Wolff camera with Co Ka radiation. High-purity Si powder was used as an internal standard for measurements of the lattice parameter. The diffraction intensity data for structure analysis were collected by an MXP 18A-HF diffractometer with rotating anode, which had an 18 kW X-ray generator and Cu Ka radiation. A graphite monochromator was also used.

3. Results and discussion

obtained only three binary Co-Si compounds: orthorhombic C0 2Si with a = 7.960 A, b = 4.918 A, c = 3.738 A; cubic CoSi with a = 4.447 A; cubic Cc'Si, with a = 5.365 A. C0 3Si is absent in our binary and ternary alloys. Boomgaard and Carpay [15] reported that C0 3Si is stable between 1170 and 1210 "C, Our samples were annealed at 800 °C, thus the C0 3Si phase did not form under our experimental conditions. 3.1.3. Nd-Si Our knowledge of the Nd-Si phase diagram is based on the work of Gokhale et al. [16]. The binary phases NdSi z, NdSi, Nd.Si, and Nd sSi3 were found to exist. Eremenko et al. [17] had already reported the NdySi, phase, but did not give its structure. The Nd 3Si 4 phase was also mentioned in Ref. [17], without data on its structure. Based on our experimental results, there is no possibility for other phases existing between NdSi and NdSi 2 , thus it is likely that these phases are unstable at 800 "C, Our results on the binary system Nd-Si are in agreement with those in the ternary system Nd-Re-Si [18].

3.1. Binary system

3.2. Ternary system

3.1.1. Nd-Co The Nd-Co system has been studied in great detail. A number of binary phases has been reported: Nd 2Co l 7 [7], NdCo s [8], Nd sCo 19 [9], Nd 2C0 7 [10], NdC0 3 [11], NdCo z [12], and Nd 3Co [13]. The binary phases Nd 2Co 17 , NdCo s, Nd sCo l 9 , NdCo 3 and NdCo z were found to exist in our binary and ternary alloys quenched from 800 "C, The four additional phases with higher neodymium contents melt at 800 °C and therefore do not appear in the 800 °C isothermal section.

No experimental work has been reported for the ternary Nd-Co-Si phase diagram. Six ternary compounds were found in both the as-cast and annealed alloys. They are NdCoSi, NdCoSi 2 , NdCozSi z, NdCoSi 3 , NdCo 11 _ xSix , and NdCo 13 _ xSix ' The structural parameters of these ternary compounds are listed in Table 1. For the NdCo 13 _ xSix solid solution, only the existence of a compound NdColO.sSi z.s with NaZn 13-type structure (Fm3c, a = 11.24 A) was reported [6]. Under our experimental conditions, it was indexed on a bodycentred tetragonal structure with space group /4/mcm derived from the NaZn 13-type. The solid solubility has been determined by a parametric method. In Fig. 1 we show the dependence of the lattice parameters a and c on the Si content x. According to the variation

3.1.2. Co-Si In the binary Co-Si system, four kinds of Co-Si compound were reported [14]: C0 3Si, C0 2Si, CoSi and CoSi z. Under our present experimental conditions, we

Table 1 List of compounds. space group, and lattice parameters of the Nd-Co-Si. ternary system Compound

Solid solubility

Space group

Lattice parameters (A)

Reference

NdCo 13_.Si.

2.5 2.5-4.5 0-1.8 2 1.2-1.8

Fm3c 141mcm R3m 14,/amd 14,/amd 141mmm 14mm Cmcm P41nmm P61mmm

a = 11.24 a = 7.811-7.763, c = 11.430-11.464 a = 8.456-8.412, c = 12.234-12.210 a = 9.794, c = 6.328

[6J This work This work [21J This work [24J [25J [26J [23J This work

Nd 2Co l 7-x Si• NdCo,I_.Si• NdCo 2Si 2 NdCoSi J NdCoSi 2 NdCoSi NdCo 0 4Si l 6

a = 3.960, c = 9.910 a = 4.123, C = 9.570 a = 4.124, b = 16.395, c = 4.045 a = 4.032, c = 6.872 a = 4.041, c = 4.253

I

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Y. Zhao et al. I Journal of Alloys and Compounds 241 (1996) 191-195

-

702 699 696 693 690 687

~

'-'" ~

,......

<

'-'"

CJ

..........

ment of the X-ray diffraction data [19] we deduced that there exist five kinds of equivalent position, i.e. 4a, 161-(1), 16k, 161(2) and 4d, which are occupied by 4Nd, 16Co [1], 16Co [2], 16(Co + Si) and 4Co [3] atoms respectively. We also used the LAZY program to calculate the X-ray diffraction intensity of NdCo l 3 _ xSix solid solution. Table 2 illustrates the calculated and observed intensities of NdCo Si solid solution. The agreement between the calcl~laXted and observed intensities suggests the atomic occupancy mentioned above. We also list indices and calculated and observed spacings and intensities for ~dCogSi4' Atomic parameters of NdCogSi4 are given 10 Table 3.

I

~-

.

ll~iH~~

HH~~

<

'-'"

a::s

2

3

193

4

Table 3 Atomic parameters for compound NdCo.Si.

X Fig. 1. The variation of the lattice parameters a and c and the unit cell volume v vs. the Si content x for NdCo l1 _ xSi •.

between the lattice parameters a and c and the Si content x, we have determined the solid solution range of NdCo 13 _ xSi x as 2.5:o;;;x:O;;; 4. From a Rietveld refine-

Atom

Position

x

y

z

N

Nd Co Co

4a 161(1) 16k 4d 161(2)

0.0000 0.1277 0.1998 0.0000 0.3294

0.0000 0.6277 0.0676 0.5000 0.8294

0.2500 0.0000 0.0000 0.0000 0.0000

4 16 16 4 16

Co Si

Table 2 List of lattice spacings. diffraction intensity and the results of indexes of compound NdCo.Si.

h I 2 2 2 0 2 2 1 2 3 2 3 3 2 3 4 3 1 3 4 2 4 4 2 3 5 3 4 5 0 1 4 4

k 1 0 1 0 0 2 1 1 2 1 0 I 2 1 2 1 3 I 3 2 0 1 0 2 3 1 1 2 1 0 1 4 0

I 2 0 1 2 4 0 3 4 2 0 4 2 1 5 3 I 0 6 2 0 6 3 4 6 4 0 6 4 2 8 8 0 6

d"h. (A) 3.9833 3.9038 3.3385 3.2292 2.8571 2.7593 2.5802 2.5503 2.4873 2.4675 2.3144 2.2674 2.1272 1.9202 1.8842 1.8675 1.8392 1.8105 1.7521 1.7447 1.7203 1.6969 1.6143 1.5740 1.5495 1.5304 1.5136 1.4917 1.4793 1.4376 1.3912 1.3793 1.3672

d,." (A) 3.9753 3.8960 3.3345 3.2238 2.8705 2.7549 2.5767 2.5457 2.4838 2.4641 2.3110 2.2643 2.1238 1.1756 1.8819 1.8648 1.8366 1.8077 1.7493 1.7424 1.7177 1.6945 1.6119 1.5717 1.5471 1.5282 1.5114 1.4895 1.4767 1.4353 1.3889 1.3775 1.3652

Ju b s

i:

h

k

I

d"h. (A)

d"k (A)

[nbs

le.1e

8 9 10 10 25 8 4 22 27 18 32 100 2 39 35 19 10 15 9 13 2 3 11 5 4 7 8 8 5 5

7 10 10 11 16 5 3 21 23 18 27 100 2 32 32 20 10 10 6 13 2 3 12 5 4 6 7 8 6 3 4 8 5

5 4 3 3 6 2 6 4 4 6 5 6 5 2 5 4 0 6 1 4 7 3 5 7 5 2 4 3 6 7 7 6

1 4 3 2 0 2 0 4 1 2 2 1 3 1 4 0 0 2 I 2 I 2 3 1 4 2 I I 3 2 3 4

4 2 6 7 0 8 2 4 7 0 5 3 4 9 3 8 10 4 10 8 0 9 6 2 5 10 9 10 5 3 0 4

1.3510 1.3416 1.3271 1.3083 1.3002 1.2749 1.2688 1.2437 1.2406 1.2339 1.2258 1.2164 1.2130 1.1988 1.1613 1.1572 1.1503 1.1339 1.1259 1.1093 1.1035 1.1001 1.0974 1.0837 1.0766 1.0610 1.0589 1.0423 1.0380 1.0323 1.0247 1.0130

1.3489 1.3394 1.3251 1.3066 1.2987 1.2729 1.2667 1.2419 1.2388 1.2320 1.2242 1.2148 1.2115 1.1980 1.1597 1.1555 1.1482 1.1322 1.1241 1.1078 1.1020 1.0986 1.0956 1.0822 1.0753 1.0598 1.0574 1.0408 1.0365 1.0308 1.0232 1.0113

4 4 11 3 2 2 I 2 4 3 5 2 2 2 2 9 2 6 2 6 2 4 4 4 2 2 3 3 3 4 4 2

5 4 8 2 2 I I 1 5 3 7 3 2 2 2 6 1 10 2 5 1 3 4 4 2 2 3 3 4 3 3 3

5 11 5

Y. Zhao et al. I Journal of Alloys and Compounds 241 (1996) 191-195

194

For NdColl_xSi x' Bodak and Gladyshevskij [20] reported that only the NdCo 9Si 2 compound exists, having BaCdll-type structure: /4 1/amd, a = 4.794 A, c = 6.328 A. However, our results show that there exists a range of solubility, 1.2:s:: x :s:: 1.8. Mayer and FeIner [21] have reported that the NdCoSi phase is isostructural with PbFCI-type (a = 4.035 A, c = 6.895 A). The same structure (P4/nmm, a = 4.032 A, c = 6.895 A) was confirmed by Bodak et al. [22] from X-ray powder analysis. Our X-ray diffraction analysis confirmed this conclusion. Rossi et al. [23] reported that NdCo 2Si 2 is tetragonal with ordered ThCr 2Si 2-type structure: /4/mmm (a = 3.960 A, c = 9.910 A). Under our experimental conditions this compound was also found and its structural data are included in Table 1. The crystal structure of the NdCoSi 3 compound, probably with BaAl 4-derivative type structure [24] and analogous to CeCoSi 3 , was reproduced in our annealed alloys. Pelizzone et al. [25] determined the structure of NdCoSi 2 as CeNiSi2-type (Cmcm, a = 4.142 A, b = 16.35 A, and c = 4.045 A), which is confirmed by our experimental result. The ternary compound NdCo o.4Si1.6' crystallizing with AIB2-type structure [24] has been identified in the Nd-Co-Si system. A summary of the phases and their structures and lattice parameters is given in Table 1. Since the X-ray diffraction patterns in the different three-phase fields surrounding a given compound did not change, we concluded that all ternary compounds are stoichiometric. Therefore, most two-phase regions are degenerate and appear as lines in Fig. 2. In the binary Nd-Co system, the liquid phase exists above 750°C in the Nd-rich region (Nd:Co atomic ratio above 1:2). The phase relations in this region have not been determined, since most of our samples in this region

Co

C02Si

remelted during annealing at 800 "C, The complete isothermal section of the Nd-Co-Si phase diagram at 800 °C is shown in Fig. 2, in which the equilibria that were not confirmed under our experimental conditions are indicated by a dotted tie-line. In Fig. 3 we show the phase distribution at the Co-rich corner. Details of the phase relations in the Nd-Co-Si ternary system are also given in Table 4. According to our experimental results, the ternary Nd-Co-Si system can be characterized by the existence of 26 three-phase regions and four two-phase regions. The mutual solid Table 4 Phase regions and phase relations in the Nd-Co-Si ternary system Phase region 1

2 3 4 5 6

9 10 11

12 13 14

15 16 17 18 19

Co

1L:.::.......L..I....:.::....:~.a.:.L....:::::~

C02Si

_ _' -

CoSi

~

5i

CoSiz

Fig. 2. Nd-Co-Si isothermal section at 800 ·C. A: NdCoSi. B: NdCo 2Si 2 • C: NdCoo.Si I 6• D: NdCoSi 2 • E: NdCoSi 3. The solid solubilities of compounds NdCo l1_.Si.. NdColI_.Si. and Nd 2Co. 7_.Si. are indicated by black dots.

CoSi

Fig. 3. The phase distribution of the Nd-Co-Si ternary system at the Co-rich corner.

7 8

Nd

~~--------""'::'I-------";::>ol,

20 21 22 23 24 25 26 27 28 29

30'

Phase composition NdCoSi + NdCo 2 + NdCo 3 NdCoSi + NdCo 3 + Nd 2C0 7 NdCoSi + NdCo 2Si 2 + Nd 2C0 7 NdCo 2Si 2 + Nd 2C0 7 + Nd,CO I9 NdCo 2Si 2 + Nd,Co. 9 + NdCo~ NdCo 2Si 2 + NdCo~ + Nd 2C0 17_.Si. NdCo~ + Nd 2Co I7_.Si. NdColI_.Si. + Nd 2C0 17_.Si. NdCo,,_.Si. + NdCo 13_.Si. NdCo,I_.Si. + Nd 2Co. 7 + Co NdColI_.Si. + NdCo 13_.Si. + Co NdCo'3_.Si. + Co 2Si + Co NdCo 13_.Si. + Co 2Si NdCo l1_.Si. + Co 2Si + CoSi NdCo 13_.Si. + CoSi + NdCo 2Si 2 NdColI_.Si. + NdCo 13_.Si. + NdCo 2Si 2 NdColI_.Si. + Nd 2Co I7_.Si. + NdCo 2Si 2 NdCo 2Si 2 + NdCoSi 2 + CoSi NdCoSi, + CoSi 2 + CoSi NdCoSi 3 + CoSi 2 + Si NdCoSi 2 + NdCoSi, + CoSi NdCoSi 2 + NdCoSi 3 + NdSi 2 NdCo 2Si 2 + NdCoSi 2 + NdCo o .Si. 6 NdSi 2 + NdCQSi 2 + NdCo n.Si l 6 NdCoSi 3 + NdSi 2 + Si NdCo 2Si 2 + NdCoSi + Nd.Si, NdCo 2Si 2 + Nd.Si, + NdSi NdCo 2Si 2 + NdCo n.Si. 6 + NdSi NdCoSi + Nd.Si, + Nd~Si3 NdCo n.Si , 6 + NdSi + NdSi 2

I

r

1

Y. Zhao et al. I Journal of Alloys and Compounds 241 (1996) 191-195

solubilities of the third constituent in Nd and Co silicides were generally found to be small. So the solubility of the third constituent in Nd and Co silicides, as well as in the binary Nd-Co compounds, appeared to be negligible in Fig. 2 (except for Nd 2Co 17 which has an extended homogeneity range with a content up to 9.5 at.% Si atoms substituting for Co atoms).

4. Conclusion In this study the isothermal section of the Nd-CoSi system in the Nd-poor region was determined at 800 "C, Seven ternary compounds were found and their solid solution ranges were determined: NdCoSi, NdCoSi 2 , NdC0 2Si 2 , NdCoSi 3 , NdCo o.4SiI. 6 ' NdCo l1 _ .. Six (1.2 ~ x ~ 1.8), and NdCo I 3 _ x Six (2.5 ~ x ~ 4), including the binary compound Nd 2Co 17 _ x Six (0 ~ x ~ 1.8). A correct crystallographic description of NdCo 13 _ .. Six with a tetragonal structure related to the NaZn 13-type was given. Details of the crystal structure and lattice parameters of all the ternary compounds were determined.

Acknowledgements This work was supported by the National Natural Science Foundation of China.

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[3] T.T.M. Palstra, J.A Mydosh, G.J. Nieuwenhuys, A.M. van der Kraan and K.H,J. Buschow, J. Magn. Magn. Mater., 36 (1983)

290. [4] T.T.M. Palstra, G.J. Nieuwenhuys, J.A Mydosh and K.H.J. Buschow, Phys. Rev. B, 31 (1985) 4622. [5] M.O. Huang, Y. Zheng, K. Miller, J. Elbicki, W.E. Wallace and S.G. Sankar, IEEE Trans. Magn., MAG-28 (1992) 2859. [6] P.1. Kripyakevich, O.S. Zarechniuk, E.1. Gladyshevskij and 0.1. Bodak, Z. Anorg. Allg. Chem., 358 (1968) 90. [7] K.H.J. Buschow, J. Less-Common Met., 11 (1966) 204. [8] E. Burzo, Int. J. Mag., 3 (1973) 161. [9] IF. Cannon, D. Robertson and H.T. Hall, Mater. Res. Bull., 7 (1972) 5. [10] R. Lemaire, Cobalt, 33 (1966) 201. [11] K.H,J. Buschow, J. Appl. Phys., 42 (1971) 3433. [12] O.D. McMasters and K.A Gschneidner, Nucl. Metal. Ser. X (1964) 93. [13] K.H.J. Buschow and AS. Van der Goot, J. Less-Common Met., 18 (1969) 309; J.L. Ferron, R. Lemaire, D. Paccard, D. Pauthenet and e.R. Acat, Sci. Paris, 267 (1968) 371. [14] K. Ishida, T. Nishizawa and M.E. Schlesinger, J. Phase Equilib., 12 (1991) 587. (15] J.Y.D. Boomgaard and F.M.A. Carpay, Acta Metall., 20 (1972) 473. [16] AB. Gokhale, A. Munitz and G.J. Abbaschian, Bull. Alloy Phase Diag., 10 (1989). [17] Y.N. Eremenko, K.A Meleshevish, Yu.I. Buyanova and I.M. Obushenko, Dop. Akad. Nauk Ukr. USR, All (1984) 77. [18] Y.K. Pecharskij, Autoreferat Dis. Kand. Khim., Nauk, Lvov, 1979, p. 23 (abstract of thesis, in Russian). [19] W. Tang, J. Liang, Y. Zhao, Y. Guo and G. Rao, J. Alloys Comp., in press. [20] 0.1. Bodak and E.I. Gladyshevskij, Dop. Akad. Nauk Ukr. USR, A5 (1969) 452. [21] I. Mayer and I. FeIner, J. Solid State Chem., 7 (1973) 292. [22] 0.1. Bodak, E.I. Gladyshevskij and P.I. Kripyakevich, Zn. Strukt. Khim., 11 (1970) 305. [23] D. Rossi, R. Marazza and R. Ferro, J. Less-Common u«. 58 (1978) 203. [24] E.1. Gladyshevskij and 0.1. Bodak, in N.M. Zhavoronkov (ed.), Khim. Met. Splavov, Nauka, Moscow, p. 46. [25] M. Pelizzone, H.P. Braun and J. Muller, J. Magn. Magn. Mater; 30 (1982) 33.