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Structure of amorphous Fe–Zr–B powders obtained by chemical reduction
Journal of Magnetism and Magnetic Materials 242–245 (2002) 621–623
Structure of amorphous Fe–Zr–B powders obtained by chemical reduction J.G. Zhanga,*, H.J. Jinb, W.X. Xub, Y.J. Lina, W.C. Wangc a b
The Institute of Advanced Materials, Technology Center, Baoshan Iron & Steel Co. Ltd, Fujin Road, Shanghai 201900, China Shanghai Iron & Steel Research Institute, Shanghai Baosteel Group Corporation, 1001 Tai He Road, Shanghai 200940, China c Department of Physics, Beijing University, Beijing 100871, China
Abstract The ultrafine amorphous Fe56Zr5B39 and Fe68B32 powders prepared by borohydride reduction were investigated . using the Mossbauer spectroscopy for a comparative study. The hyperfine field distribution PðHÞ of the Fe56Zr5B39 powder shows a double-maxima function of H with a high-field component at 210 kOe and a low-field component at 48 kOe. The EXAFS investigation on the Fe56Zr5B39 powders revealed the short-range order structure in the powders, which coincides with the behavior of PðHÞ: r 2002 Elsevier Science B.V. All rights reserved. . Keywords: Amorphous system; Fine particles; Mossbauer spectroscopy; Fe alloys; EXAFS; Hyperfine field distribution
Recent studies on the ultrafine amorphous alloy powders prepared by chemical reduction have attracted much attention because the powders have been expected to be applied to powder metallurgy, magnetic recording, catalysis, and ferrofluids by taking advantage of the novel physical and chemical properties resulting from their fine particle size and amorphous state. Several alloy systems were dealing with so far: (1) Fe–C powders which were prepared by thermal decomposition of Fe(CO)5 [1]; (2) Fe–M–B (M: Ni, Co, etc.) powders were produced by the reduction of metal salts with an alkali metal borohydride in aqueous solutions [2]; (3) Ni–Mo–B powders were obtained by the reduction of Na2MoO4 as a molybdenum salt using KBH4 as a reducing agent [3]; (4) Co–Pt–B powders were prepared by the reduction of CoCl2 6H2O and PtCl4 with NaBH4 [4]. The Fe–Zr–B amorphous powders, which were first prepared successfully by the present authors using chemical reduction and reported in 1998 [5], are of great interest due to the fact that it contains both metalloids and early transition metals. It has been established that Fe–B alloys favor high-moment states, whereas in Fe–Zr *Corresponding author. Tel.: +86-21-567-80880ext.2205; fax: +86-21-566-08-212. E-mail address: [email protected] (J.G. Zhang).
alloys low-moment states are observed and are associated with the competing ferro- and antiferro-magnetic exchange interactions. Previous X-ray diffraction carried out on Fe–Zr–B powders obtained by chemical reduction displayed two halos [5]. Actually, the two halos of the X-ray diffraction pattern were also observed in other materials [6,7], but no detailed mechanism has been reported. Obviously, the X-ray diffraction pattern with two halos implies a novel complicated structure in the powders, which could be related with the well-known fact that there are a large number of structurally and magnetically nonequivalent sites in amorphous magnetic solids. But at present our knowledge of the details of the novel complicated structure still remains insufficient. In this . paper, Mossbauer spectroscopy and extended X-ray absorption fine structure (EXAFS) investigations on the ultrafine amorphous Fe–Zr–B powders prepared by borohydride reduction were performed in order to study the details of the novel complicated structure of the powders. Ultrafine amorphous Fe–Zr–B powders were prepared by the reduction of aqueous solutions of metallic salts using an alkali metal borohydride. The 0.1 mol/L metallic salt solutions of Fe+Zr with different ratios of FeSO4 to Zr(SO4)2 were prepared. Then a NaBH4 or
0304-8853/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 1 ) 0 1 0 4 2 - 3
622
J.G. Zhang et al. / Journal of Magnetism and Magnetic Materials 242–245 (2002) 621–623
KBH4 aqueous solution of 0.5 mol/L was added to the above metallic salt solutions with vigorous stirring. The reactions were carried out in air. The black precipitates were immediately treated by a chromatic procedure in a potassium dichromate solution. The chromatic powders were collected on a filter, washed, and dried at room temperature in vacuum. The ultrafine amorphous Fe–B powders were also prepared by chemical reduction for a comparative study. The chemical composition of the powder was . determined by wet-chemical method. Mossbauer spectra were obtained by a constant-acceleration spectrometer with a 10 mCi (milliCuries) source of 57Co in rhodium. The measurements of X-ray absorption spectra were taken at the EXAFS station of synchrotron radiation in BEPC NL (Beijing Electron Positron Collider National Laboratory) in transmission mode. The details of the experimental procedure and data analysis of EXAFS investigation were reported in Ref. [8]. The chemical compositions of the Fe–B and Fe–Zr–B powders prepared in this study are as follows (at%):
Sample A: Fe 68.0, B 32.0; Sample B: Fe 55.7, Zr 5.3, B 39.0. . Figs. 1 and 2 present the Mossbauer spectra and the corresponding hyperfine field distributions of sample B (Fe56Zr5B39) and sample A (Fe68B32), respectively. The broadened sextet shown in Figs. 1 and 2 gives further evidence for the amorphous state of the powders. The . Mossbauer parameters of sample A (Fe68B32) and sample B (Fe56Zr5B39) are given in Table 1. As can be seen from Table 1, the line intensity ratio I225 =I126 suggests an almost random distribution of spin orientations in both Fe68B32 and Fe56Zr5B39 powders. Table 1 also indicates that the values of both the Hpeak and Hmean in the Fe56Zr5B39 powders are smaller than those in the Fe68B32 powders. Jiang et al. [9] reported that Hmean equals 230 kOe in the Fe79B21 powders and 244 kOe in the Fe80B20 ribbon, which are larger than those shown in Table 1. The main result is a decrease of the average hyperfine field with increasing boron content; this may indicate that with increasing boron content, the transfer of the 2p electrons in boron atoms
. Fig. 1. (A) Mossbauer spectrum and (B) magnetic hyperfine field distributions of the Fe56Zr5B39 powders.
. Fig. 2. (A) Mossbauer spectrum and (B) magnetic hyperfine field distributions of the Fe68B32 powders.
J.G. Zhang et al. / Journal of Magnetism and Magnetic Materials 242–245 (2002) 621–623
623
Table 1 . Mossbauer parameters of the Fe68B32 and the Fe56Zr5B39 powders Sample
I 225 =I 126
FWHM (kOe)
Hpeak (kOe)
Hmean (kOe)
A (Fe68B32) B (Fe56Zr5B39)
2.1/3.0 2.2/3.0
113 115
235 210
215 188
I25 =I16 is the line intensity ratio; FWHM is the full width at half maximum; Hpeak is the hyperfine field corresponding to the maximum in PðHÞ; Hmean is the mean value of the hyperfine field. Table 2 The near neighbor structural parameters of the ultrafine amorphous Fe56Zr5B39 powders Sample
Central atom
Atom pairs
Distance (nm)
Coordination number
Fe56Zr5B39
Fe Fe Zr Zr Zr Zr
Fe–Fe Fe–Fe Zr–B Zr–B Zr–Fe Zr–Zr
0.213 0.246 0.224 0.249 0.284 0.323
2.2 7.6 3.7 1.8 3.0 7.4
to the 3d bands of iron atoms also increases. The full widths at half maximum (FWHM) in the hyperfine field distribution in both of the Fe56Zr5B39 and the Fe68B32 powders are wide and very close to that of 118 kOe reported in the Ref. [9]. The wide hyperfine distributions of the powders prepared by chemical reduction may reflect a distribution of compositions in the powders. The hyperfine field distributions PðHÞ shown in Figs. 1 and 2 exhibit a number of unusual features. As compared with only one main peak at 235 kOe in the distribution of the Fe68B32 powders, the PðHÞ of the Fe56Zr5B39 powders can be approximately described by a double-maxima function of H with a high-field component at 210 kOe and a low-field component at 48 kOe. From this comparison it is reasonable to associate the low-field component of the Fe56Zr5B39 powders with Fe atoms that have a substantial number of Zr neighbors. The high-field component of the Fe56Zr5B39 powders is due to Fe atoms that have primarily Fe, B, and possibly some Zr as their nearest neighbors. The short-range order structural parameters indicated in Table 2 were obtained by the EXAFS investigation on the Fe56Zr5B39 powders. As shown in Table 2, the shortrange order structure around Fe is very different from that around Zr, and at least two chemically different iron neighbors exist in the Fe56Zr5B39 powders. Therefore, the short-range order structure in the Fe56Zr5B39 powders revealed by the EXAFS investigation is in agreement with the behavior of the hyperfine field . distributions PðHÞ deduced from the Mossbauer spectra. As a conclusion, the hyperfine field distributions PðHÞ of the Fe56Zr5B39 powders prepared by borohydride reduction exhibit a two-maxima function of H; whereas a single-maximum function is observed in the Fe68B32 powders. The low-field component of PðHÞ in the
Fe56Zr5B39 powders originates primarily from the Fe atoms that have a substantial number of Zr neighbors. The high-field component of PðHÞ in the Fe56Zr5B39 powders is due to Fe atoms that have primarily Fe, B, and possibly some Zr as their neighbors. The behavior of the hyperfine field distributions PðHÞ of the Fe56Zr5B39 powders is in agreement with the shortrange order structure revealed by EXAFS investigation. The authors gratefully acknowledge the financial support of National Science Foundation of China (59771027).
References [1] J. Wonterghem, S. Morup, S.W. Charles, S. Wells, J. Villadsen, Phys. Rev. Lett. 55 (1985) 410. [2] J.G. Zhang, J. Mater. Eng. Perform. 4 (1995) 453. [3] J. Saida, E. Akiyama, K. Hashimoto, A. Inoue, T. Masumoto, J. Japan Inst. Metals 60 (1996) 79. [4] L. Yiping, Z.X. Tang, G.C. Hadjipanayis, C.M. Sorensen, K.J. Klabunde, IEEE Trans. Magn. 29 (1993) 2646. [5] J.G. Zhang, Y.J. Lin, W.X. Xu, H.J. Jin, in: M.A. Imam, R. DeNale, S. Hanada, Z. Zhong, D.N. Lee (Eds.), Proceedings of the Third Pacific Rim International Conference on Advance Materials and Process. (PRICM-3), The Minerals, Metals & Materials Society, Hawaii, 1998, p. 981. [6] J. Eckert, U. Kuhn, N. Mattern, A. Reger-Leonhard, M. Heilmaier, Scr. Mater. 44 (2001) 1587. [7] M.G. Ferreira, D. Silva, M.A. Valente, J. Mater. Sci. 36 (2001) 213. [8] W.C. Wang, Y. Chen, J.G. Zhang, T.D. Hu, J. Non. Cryst. Solids 160 (1993) 268. [9] J. Jiang, I. Dezsi, U. Gonser, J. Weissmuller, J. Non-Cryst. Solids 116 (1990) 247.
Structure of amorphous Fe–Zr–B powders obtained by chemical reduction J.G. Zhanga,*, H.J. Jinb, W.X. Xub, Y.J. Lina, W.C. Wangc a b
The Institute of Advanced Materials, Technology Center, Baoshan Iron & Steel Co. Ltd, Fujin Road, Shanghai 201900, China Shanghai Iron & Steel Research Institute, Shanghai Baosteel Group Corporation, 1001 Tai He Road, Shanghai 200940, China c Department of Physics, Beijing University, Beijing 100871, China
Abstract The ultrafine amorphous Fe56Zr5B39 and Fe68B32 powders prepared by borohydride reduction were investigated . using the Mossbauer spectroscopy for a comparative study. The hyperfine field distribution PðHÞ of the Fe56Zr5B39 powder shows a double-maxima function of H with a high-field component at 210 kOe and a low-field component at 48 kOe. The EXAFS investigation on the Fe56Zr5B39 powders revealed the short-range order structure in the powders, which coincides with the behavior of PðHÞ: r 2002 Elsevier Science B.V. All rights reserved. . Keywords: Amorphous system; Fine particles; Mossbauer spectroscopy; Fe alloys; EXAFS; Hyperfine field distribution
Recent studies on the ultrafine amorphous alloy powders prepared by chemical reduction have attracted much attention because the powders have been expected to be applied to powder metallurgy, magnetic recording, catalysis, and ferrofluids by taking advantage of the novel physical and chemical properties resulting from their fine particle size and amorphous state. Several alloy systems were dealing with so far: (1) Fe–C powders which were prepared by thermal decomposition of Fe(CO)5 [1]; (2) Fe–M–B (M: Ni, Co, etc.) powders were produced by the reduction of metal salts with an alkali metal borohydride in aqueous solutions [2]; (3) Ni–Mo–B powders were obtained by the reduction of Na2MoO4 as a molybdenum salt using KBH4 as a reducing agent [3]; (4) Co–Pt–B powders were prepared by the reduction of CoCl2 6H2O and PtCl4 with NaBH4 [4]. The Fe–Zr–B amorphous powders, which were first prepared successfully by the present authors using chemical reduction and reported in 1998 [5], are of great interest due to the fact that it contains both metalloids and early transition metals. It has been established that Fe–B alloys favor high-moment states, whereas in Fe–Zr *Corresponding author. Tel.: +86-21-567-80880ext.2205; fax: +86-21-566-08-212. E-mail address: [email protected] (J.G. Zhang).
alloys low-moment states are observed and are associated with the competing ferro- and antiferro-magnetic exchange interactions. Previous X-ray diffraction carried out on Fe–Zr–B powders obtained by chemical reduction displayed two halos [5]. Actually, the two halos of the X-ray diffraction pattern were also observed in other materials [6,7], but no detailed mechanism has been reported. Obviously, the X-ray diffraction pattern with two halos implies a novel complicated structure in the powders, which could be related with the well-known fact that there are a large number of structurally and magnetically nonequivalent sites in amorphous magnetic solids. But at present our knowledge of the details of the novel complicated structure still remains insufficient. In this . paper, Mossbauer spectroscopy and extended X-ray absorption fine structure (EXAFS) investigations on the ultrafine amorphous Fe–Zr–B powders prepared by borohydride reduction were performed in order to study the details of the novel complicated structure of the powders. Ultrafine amorphous Fe–Zr–B powders were prepared by the reduction of aqueous solutions of metallic salts using an alkali metal borohydride. The 0.1 mol/L metallic salt solutions of Fe+Zr with different ratios of FeSO4 to Zr(SO4)2 were prepared. Then a NaBH4 or
0304-8853/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 1 ) 0 1 0 4 2 - 3
622
J.G. Zhang et al. / Journal of Magnetism and Magnetic Materials 242–245 (2002) 621–623
KBH4 aqueous solution of 0.5 mol/L was added to the above metallic salt solutions with vigorous stirring. The reactions were carried out in air. The black precipitates were immediately treated by a chromatic procedure in a potassium dichromate solution. The chromatic powders were collected on a filter, washed, and dried at room temperature in vacuum. The ultrafine amorphous Fe–B powders were also prepared by chemical reduction for a comparative study. The chemical composition of the powder was . determined by wet-chemical method. Mossbauer spectra were obtained by a constant-acceleration spectrometer with a 10 mCi (milliCuries) source of 57Co in rhodium. The measurements of X-ray absorption spectra were taken at the EXAFS station of synchrotron radiation in BEPC NL (Beijing Electron Positron Collider National Laboratory) in transmission mode. The details of the experimental procedure and data analysis of EXAFS investigation were reported in Ref. [8]. The chemical compositions of the Fe–B and Fe–Zr–B powders prepared in this study are as follows (at%):
Sample A: Fe 68.0, B 32.0; Sample B: Fe 55.7, Zr 5.3, B 39.0. . Figs. 1 and 2 present the Mossbauer spectra and the corresponding hyperfine field distributions of sample B (Fe56Zr5B39) and sample A (Fe68B32), respectively. The broadened sextet shown in Figs. 1 and 2 gives further evidence for the amorphous state of the powders. The . Mossbauer parameters of sample A (Fe68B32) and sample B (Fe56Zr5B39) are given in Table 1. As can be seen from Table 1, the line intensity ratio I225 =I126 suggests an almost random distribution of spin orientations in both Fe68B32 and Fe56Zr5B39 powders. Table 1 also indicates that the values of both the Hpeak and Hmean in the Fe56Zr5B39 powders are smaller than those in the Fe68B32 powders. Jiang et al. [9] reported that Hmean equals 230 kOe in the Fe79B21 powders and 244 kOe in the Fe80B20 ribbon, which are larger than those shown in Table 1. The main result is a decrease of the average hyperfine field with increasing boron content; this may indicate that with increasing boron content, the transfer of the 2p electrons in boron atoms
. Fig. 1. (A) Mossbauer spectrum and (B) magnetic hyperfine field distributions of the Fe56Zr5B39 powders.
. Fig. 2. (A) Mossbauer spectrum and (B) magnetic hyperfine field distributions of the Fe68B32 powders.
J.G. Zhang et al. / Journal of Magnetism and Magnetic Materials 242–245 (2002) 621–623
623
Table 1 . Mossbauer parameters of the Fe68B32 and the Fe56Zr5B39 powders Sample
I 225 =I 126
FWHM (kOe)
Hpeak (kOe)
Hmean (kOe)
A (Fe68B32) B (Fe56Zr5B39)
2.1/3.0 2.2/3.0
113 115
235 210
215 188
I25 =I16 is the line intensity ratio; FWHM is the full width at half maximum; Hpeak is the hyperfine field corresponding to the maximum in PðHÞ; Hmean is the mean value of the hyperfine field. Table 2 The near neighbor structural parameters of the ultrafine amorphous Fe56Zr5B39 powders Sample
Central atom
Atom pairs
Distance (nm)
Coordination number
Fe56Zr5B39
Fe Fe Zr Zr Zr Zr
Fe–Fe Fe–Fe Zr–B Zr–B Zr–Fe Zr–Zr
0.213 0.246 0.224 0.249 0.284 0.323
2.2 7.6 3.7 1.8 3.0 7.4
to the 3d bands of iron atoms also increases. The full widths at half maximum (FWHM) in the hyperfine field distribution in both of the Fe56Zr5B39 and the Fe68B32 powders are wide and very close to that of 118 kOe reported in the Ref. [9]. The wide hyperfine distributions of the powders prepared by chemical reduction may reflect a distribution of compositions in the powders. The hyperfine field distributions PðHÞ shown in Figs. 1 and 2 exhibit a number of unusual features. As compared with only one main peak at 235 kOe in the distribution of the Fe68B32 powders, the PðHÞ of the Fe56Zr5B39 powders can be approximately described by a double-maxima function of H with a high-field component at 210 kOe and a low-field component at 48 kOe. From this comparison it is reasonable to associate the low-field component of the Fe56Zr5B39 powders with Fe atoms that have a substantial number of Zr neighbors. The high-field component of the Fe56Zr5B39 powders is due to Fe atoms that have primarily Fe, B, and possibly some Zr as their nearest neighbors. The short-range order structural parameters indicated in Table 2 were obtained by the EXAFS investigation on the Fe56Zr5B39 powders. As shown in Table 2, the shortrange order structure around Fe is very different from that around Zr, and at least two chemically different iron neighbors exist in the Fe56Zr5B39 powders. Therefore, the short-range order structure in the Fe56Zr5B39 powders revealed by the EXAFS investigation is in agreement with the behavior of the hyperfine field . distributions PðHÞ deduced from the Mossbauer spectra. As a conclusion, the hyperfine field distributions PðHÞ of the Fe56Zr5B39 powders prepared by borohydride reduction exhibit a two-maxima function of H; whereas a single-maximum function is observed in the Fe68B32 powders. The low-field component of PðHÞ in the
Fe56Zr5B39 powders originates primarily from the Fe atoms that have a substantial number of Zr neighbors. The high-field component of PðHÞ in the Fe56Zr5B39 powders is due to Fe atoms that have primarily Fe, B, and possibly some Zr as their neighbors. The behavior of the hyperfine field distributions PðHÞ of the Fe56Zr5B39 powders is in agreement with the shortrange order structure revealed by EXAFS investigation. The authors gratefully acknowledge the financial support of National Science Foundation of China (59771027).
References [1] J. Wonterghem, S. Morup, S.W. Charles, S. Wells, J. Villadsen, Phys. Rev. Lett. 55 (1985) 410. [2] J.G. Zhang, J. Mater. Eng. Perform. 4 (1995) 453. [3] J. Saida, E. Akiyama, K. Hashimoto, A. Inoue, T. Masumoto, J. Japan Inst. Metals 60 (1996) 79. [4] L. Yiping, Z.X. Tang, G.C. Hadjipanayis, C.M. Sorensen, K.J. Klabunde, IEEE Trans. Magn. 29 (1993) 2646. [5] J.G. Zhang, Y.J. Lin, W.X. Xu, H.J. Jin, in: M.A. Imam, R. DeNale, S. Hanada, Z. Zhong, D.N. Lee (Eds.), Proceedings of the Third Pacific Rim International Conference on Advance Materials and Process. (PRICM-3), The Minerals, Metals & Materials Society, Hawaii, 1998, p. 981. [6] J. Eckert, U. Kuhn, N. Mattern, A. Reger-Leonhard, M. Heilmaier, Scr. Mater. 44 (2001) 1587. [7] M.G. Ferreira, D. Silva, M.A. Valente, J. Mater. Sci. 36 (2001) 213. [8] W.C. Wang, Y. Chen, J.G. Zhang, T.D. Hu, J. Non. Cryst. Solids 160 (1993) 268. [9] J. Jiang, I. Dezsi, U. Gonser, J. Weissmuller, J. Non-Cryst. Solids 116 (1990) 247.