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在金属间化合物的结构演变中, 原子尺寸因素起着重要的作用. 由于密堆积效应, 不同原子半径比的元素往往形成不同的结构. 而自由电子填充于原子构成的晶体结构的间隙中, 它对化合物的结构也有影响. 基于组合结构化合物Ho2Ni7-xFex, 结合原子尺寸与自由电子对晶体结构的不同影响, 文章探讨一种单位体积内自由电子浓度的经验方法来判断Ho2Ni7-xFex 化合物中两种异构体间的转变. 随着Fe含量的增加, Ho2Ni7-xFex化合物先结晶成Gd2Co7型三方结构, 然后结晶成Ce2Ni7 型六方结构. 利用Rietveld精修技术和磁测量, 获得了化合物的晶体结构参数和饱和磁化强度. 化合物晶胞常数随Fe含量增加而增加, 饱和磁化强度则随之减少(d Ms/d x=-2). 分析结果表明, 单位体积内自由电子浓度更高, 化合物形成三方结构, 反之则形成六方结构.
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关键词:
- 组合结构 /
- Ho2Ni7-xFex化合物 /
- 晶体结构转变 /
- 磁性
Based on the composite compounds Ho2Ni7-xFex (x=0-3.0), a method of describing the structure transition from rhombohedral to hexagonal is discussed in terms of free electron concentration. The transition is investigated by X-ray powder diffraction and magnetic analysis. The compounds crystallize into the rhombohedral Gd2Co7-type structure for x=0-0.5 and into the hexagonal Ce2Ni7-type structure for x=0.5-2.5. The values of lattice parameters a and c of the Ho2Ni7-xFex compounds increase with the addition of Fe, and the saturation magnetization Ms decreases with Fe content increasing at a rate of d Ms/d x=-2, manifesting antiparallel alignments of the Fe and Ho moment. The higher the free electron concentration, the stabler the rhombohedral structure is, otherwise the hexagonal structure is stabler, which provides a meaningful parameter to distinguish the two allotropies in composite structure intermetallics.-
Keywords:
- composite structure /
- Ho2Ni7-xFex compounds /
- structure transition /
- magnetism
[1] Parthé E, Chabot B 1984 Handbook on the Physics and Chemistry of Rare Earths Vol. 7 (Amsterdam: North-Holland) p186
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[4] von Ranke P J, de Oliveira N A, de Sousa V S R, Garcia D C, de Oliveira I G, Magnus A, Carvallho G, Gama S 2007 J. Magn. Magn. Mater. 313 176
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[7] Khan Y 1974 Acta Cryst. B 30 861
[8] Lemaire R, Paccard D, Pauthenet R 1967 C. R. Acad. Sci. Paris B 265 1280
[9] Rietveld H M 1967 Acta Crystallogr. 22 151
[10] Rodríguez-Carvajal J 1993 Physica B 192 55
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[12] Strnat K J, Ray A E, Mildrum H F 1977 IEEE Trans. Magn. 13 1323
[13] Parviainen S, Jaakkola S 1975 EPS Conf. Abstracts 1A 33
[14] Buschow K H J 1968 J. Less-Common Metals 16 45
[15] Buschow K H J 1970 Les Eléments de Terres Rares Vol. I (Paris: CNRS)
[16] Taylor K N R, Darby M I 1972 Physics of Rare Earth Solids (London: Chapman and Hall Ltd)
[17] Elliott R J 1972 Magnetic Properies of Rare Earth Metals (New York: Plenum)
[18] Yang Y Q, Rao G H, Wang T, Li J B, Luo J, Liu G Y, Chen X J, Zhao J L 2010 J. Alloys Compd. 506 766
[19] Yang Y Q, Li G N, Wang T, Huang Q, Gao Q Q, Li J B, Liu G Y, Luo J, Rao G H 2011 Chin. Phys. B 20 106101
[20] Bartashevich M I, Mushnikov N V, Andreev A V, Goto T 2009 J. Alloys Compd. 478 34
[21] Virkar A V, Raman A 1969 J. Less-Common Metals 18 59
[22] Miyazaki T, Takahashi M, Yang X B, Saito H, Takahashi M 1988 J. Magn. Magn. Mater. 75 123
[23] Lemaire R, Paccard D 1969 Bull. Soc. Fr. Mineral. Cristallogr. 92 9
[24] Daniel C F 2011 J. Am. Chem. Soc. 133 10070
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[1] Parthé E, Chabot B 1984 Handbook on the Physics and Chemistry of Rare Earths Vol. 7 (Amsterdam: North-Holland) p186
[2] Pecharsky V K, Gschneidner Jr K A 1999 J. Magn. Magn. Mater. 200 44
[3] von Ranke P J, Pecharsky V K, Gschneidner Jr K A 1998 Phys. Rev. B 58 12110
[4] von Ranke P J, de Oliveira N A, de Sousa V S R, Garcia D C, de Oliveira I G, Magnus A, Carvallho G, Gama S 2007 J. Magn. Magn. Mater. 313 176
[5] Campoy J C P, Plaza E J R, Coelho A A, Gama S 2006 Phys. Rev. B 74 134410
[6] Buschow K H J 1977 Rep. Prog. Phys. 40 1179
[7] Khan Y 1974 Acta Cryst. B 30 861
[8] Lemaire R, Paccard D, Pauthenet R 1967 C. R. Acad. Sci. Paris B 265 1280
[9] Rietveld H M 1967 Acta Crystallogr. 22 151
[10] Rodríguez-Carvajal J 1993 Physica B 192 55
[11] Buschow K H J, van der Goot A S 1970 J. Less-Common Metals 22 419
[12] Strnat K J, Ray A E, Mildrum H F 1977 IEEE Trans. Magn. 13 1323
[13] Parviainen S, Jaakkola S 1975 EPS Conf. Abstracts 1A 33
[14] Buschow K H J 1968 J. Less-Common Metals 16 45
[15] Buschow K H J 1970 Les Eléments de Terres Rares Vol. I (Paris: CNRS)
[16] Taylor K N R, Darby M I 1972 Physics of Rare Earth Solids (London: Chapman and Hall Ltd)
[17] Elliott R J 1972 Magnetic Properies of Rare Earth Metals (New York: Plenum)
[18] Yang Y Q, Rao G H, Wang T, Li J B, Luo J, Liu G Y, Chen X J, Zhao J L 2010 J. Alloys Compd. 506 766
[19] Yang Y Q, Li G N, Wang T, Huang Q, Gao Q Q, Li J B, Liu G Y, Luo J, Rao G H 2011 Chin. Phys. B 20 106101
[20] Bartashevich M I, Mushnikov N V, Andreev A V, Goto T 2009 J. Alloys Compd. 478 34
[21] Virkar A V, Raman A 1969 J. Less-Common Metals 18 59
[22] Miyazaki T, Takahashi M, Yang X B, Saito H, Takahashi M 1988 J. Magn. Magn. Mater. 75 123
[23] Lemaire R, Paccard D 1969 Bull. Soc. Fr. Mineral. Cristallogr. 92 9
[24] Daniel C F 2011 J. Am. Chem. Soc. 133 10070
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