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The electron diffraction patterns(EDPS) of Nd1+ϵFe4B4 compounds
Scripta METALLURGICA
THE ELECTRON
Vol. 23, pp. 743-746, 1989 Printed in the U.S.A.
DIFFRACTION
PATTERNS(EDPS)
Pergamon Press plc All rights reserved
OF NdI+£Fe4B 4 COMPOUNDS
Zhao Zhibo* Ma Ruzhang* Miao Baihe** *:Department of Materials Physics, Beijing University of Science ann Technology, Beijing, P. R. China. *~:Department of Material Science and Engineering, Beijing University of Science and Technology, Beijing, P. R. China. (Received February 3, 1988) (Revised February 24, 1989) ~ntroduction The promising permanent magnet Nd-Fe-B was elaborated on by Sagawa et al in 1983(I). The existence and the unique crystal structure o£ the so calle0 boronrich phase have been described recently (2,3). The results of composition analysis and the structure refinements indicate that the chemical formula of the boron -rich phase in Nd-Fe-B system should be written as N d I ~ F e 4 B 4 ( ~ = 0 . 1 ) . similar structural properties can occur if Nd is replaced by Other rare earth elements. It is well known that more and more incommensurate modulated crystal structures are being found in nature, but less frequent are the so called incommensurate composite crystal structures which are composed of two or more mutuallj incommensurate subsystems. The RI~¢Fe4B4(R represents rare earth elements) serie s may belong to this type of com~6~nd. X-ray diffraction studies and MGssbauer investigations on some members of the series of the R. - F ~ B 4 compounds have been reported by several authors(2-8). The purpose of our ~8~k is to investigate the Ndx~fFe4B 4 compounds as an example of this series by means of a transmission electro~-~icroscope,which can overcome the inhomogeneity of the bulk samples and reflect nonstatistical information of NdI+~Fe4B4 crystals. According to the results of X-ray diffraction, the crystal structures of the compounds R , ~ F e 4 B 4 can all be divided into two interpenetratin~ substructures: R s u b s t r u c t u r @ ~ a n d Fe-B substructures: both have tetragonal symmetry. In the R substructures, R atoms form the linear strings along the ~ direction at (I/4,3/4) and (3/4,1/4) posltionS. Iron atoms build the chains of edge-sharing tetraheara parallel to the ~ axis, centered at (I/4,1/4) ano (3/4,3/4)- The boron atoms are filled inside the channels in the form of pairs, which connect the R chains and the framework formed by iron tetrahedra. Two substructures have the same tetragonal basal plane and the lattice parameters are about a=0.705-0.716 nm(3). The most interesting feature is that they have different periods in the ~ direction. Such characteristics hence give them the names vernier ~tructure@ or chimne2l@dder ~tructures. They were originally found to exist in Mn-si alloys and other related systems(9,10), since the value of c(Fe-B)/c(R), (c(Fe-B)=0.390-O.392 nm and c(R)=0.341-0.353 nm(3)) , can not be expressed by the ratio of two relatively small integers, the crystal structures of the compounds are either incommensurate or have an unusually long period in the ~ direction. Whether or not the commensurate long period superstructure exists can not be determined from the resolution of the presently available X-ray diffraction data. One can of course always find two integers m and n, within a specified tolerance, to meet the need of m/n= c(Fe-B)/c(R) and hence, the commensurate models with the formulae Rm(Fe4B4)" can be constructed although their physical justification is still questionable. The crystal structures of the R , + ~ F e 4 ~ compounds for R=Nd,Sm and Gd have been refined under the commensuratd models w i t h the chemical formulae NdsFe18B18(i.e. NdIo(Fe4B4)9), Sm77(Fe4B4)Isand Gds(Fe4B4)z , respectivel~. In all cases, the modulation of iron tetrahedra was observed.
743 0036-9748/89 $3.00 + .00 Copyright (c) 1989 Pergamon Press plc
744
Nd-Fe-B COMPOUNDS
Vol. 23, No. 5
Experimental Procedure Alloys with nominal compositions around Nd I iFe4 ~ were prepared by induction melting of pure Nd, Fe and the compacted amor~hdus boron constituents. The ingots were sealed in evacuated quartz tubes and annealed at 1300 K for 40 days. X-ray and M~ssbauer investigations have shown that these samples mainly consist of the ternary compounds NdI~£Fe4B 4 and a small amount of impurity phases(8). For the preparation of the TEM specimen, the ingots were crushed into small fragments. They were dispersed in ethyl alcohol and collected on a carbon-coated,perforated plastic film supported by a copper mesh of 3 mm diameter. Suitable fragments were selected for observation on the H-800 TEM at the operating voltage 200 kV. Results and Simple InterPretation The reflections in the EDPs of the compounds NdI.~Fe4B 4 can be classified into three species: the basic reflections of the Fe-B sd~structure, the basic reflections of the Nd substructure and the superlattice spots, i.e. the satellites due to the interaction(coupling) between two substructures. It can be observed that the satellites appear only in the cases that the electron beam is perpendicular to the ~ axis, which indicates that the long period (even incommensurate) modulation only exists in the ~ direction. Four indices(hkl112) are adopted to index the basic reflections in view of the characteristics of the double-periodicity in this system. Since the Fe-B substructure and the Nd substructure have the same tstragonal basal plane, the (hkO0) reflections are attributed to the whole crystal structure, i.e. both Fe-B substructure and Nd substructure. We suppose that the indices (hkl10) and (hkOl2) represent the basic reflections due to the Fe-B sublattice and the Nd sublattlce, respectively. The EDPs of the N d .+. F e 4 B 4 exhibit variety with respect to the results of X-ray diffraction. No u n ~ e relation exists between the observed phases and the nominal composition of the prepared samples. Although showing clear similarities for same zones, the slight different characteristics of the diffraction patterns can be observed in alloys whose compositions are around Ndl ~Fe4B4, even in the same bulk samples, which implies that the samples are very in~G~ogeneous, even after a long period of annealing treatment. Here the crystals exhibiting distinctive features of the EDPs are defined as different phases of NdI+£Fe4B 4 compounds. I. The (001)* pattern is given in Fig. 1. It can be found that the reflections (hkO0) appear only for h+k=2n (n an integer). The extinction rule reveals that there is a concealed diagonal glide plane along the 4-fold axis, which is in accord with the space groups of the Fe-B substructure(P42/ncm) and of the Nd substructure(I4/mmm) simultaneously. Fig.2 is the diffraction pattern(102)* which is attributed to the Fe-B substructure alone. In this EDP, the (010),(030) etc. reflections which violate the extinction rules in the space group P42/ncm appear. we propose that this can be explained by a double diffraction effect. One of the possible combinations of the pairs of diffraction vecters is shown in the illustration of Fig.2. It can be noted that both (001)* and (I02)F~4 are all formed by the basic reflections of Nd~+#Fe4B 4 compounds. No remarkable changes of such ba sic patterns i.e. patterns f6~led only by the basic reflections, can be observed for different phases of the NdI+~Fe4B 4 compounds. 2.Another type of basic pattern in the (uvO)* sections alsqodoes not change between the different N d ~ f F ~ B 4 compounds(e.g, see Fig.4(a))?~This type of basic pattern with which the (G~B)* sections are indexed is only a ~art of a whole (uvO)* pattern.Each basic reflection can be attributed to either the Fe-B substructure, or the Nd substructure, or to both of them. The basic patterns, however, can not give information about the superstructures coupled by two substructures. The most typical and useful EDPs are the (uvO)* sections, in which a variety of characteristics, due to the appearances of the satellites, can be found. The (100)* pattern of one fragment of the Nd~ IFe4B4 alloy is given in Fig.3 and the basic reflections are indexed according ~6 Fig.4(a). The satellites are arran&ed as chains along the ~ direction. Their intensity distribution is irregular possibly due to both the intrinsic structural properties of the vernier structure and the dynamical effect of electron diffraction. Let us consider an idealized vernier structure in which a perfect long period ordering is supposed to exist and other
Vol.
23, No.
5
Nd-Fe-B
COMPOUNDS
745
deflects are also neglected. The ('ist~ibution of the satellites is decided by periodicity(if any) of the superstructure. Further considering the Ndl0(FedP4)9 phase whose crystal structure has been refined in the supercell with c=10c(Nd)=9c(Fe-B), we can get the diffraction pattern shown in ~ig.4(b) subsequent to Fig.4(a). It can be seen that ~t is in accord with the (~O0)~ pattern in Fig. 3, qualitatively; it seems to us that the commensurate model adopted in the X-ray structure analysis (2) is reasonable. Two unexpected strong spots, however, are observed at satellite positions indicated by the arrows in Fig.3. No presently available structural knowledge of the vernier stm~cture can give an interpretation of these. We propose that the unexpected strong intensity originates in double diffraction in which very strong spots, i.e., the Nd basic reflections (0101),(0~01),(010~) snd (0~0~), are involved. The illustration is shown in Fig.4(b) by the parallelogram. 3. The most interesting type of (uvO)* section can be found occasionally. A typical example is shown in Fig. 5. With reference to the Fe-B substructure, it is indexed as the (~30)* zone. It can be observed that rows of closely s p a c e d ~ p o t s around the Fe-B basic reflections are clearly misorlented relative to the cFe.s direction. This kind of characteristic does not change as the specimen is slightly tilted with respect to the incident electron beam, which implies that the inclination of the spot rows is really related to a unique aspect of the structural properties of the selected cryst~l. The enclosed angles are somewhat variable for different selected fragments exhibiting similar effect. Here we name this phenomenon the orientation snomal~; ,n analogous situation has been found to exist in the tantalum and niobium pentoxlde systems(t1). The X-ray diffraction results on NdI+~Ve4P4(2) fsil to give an explanation of this kind of diffraction pattern. ~or understanding of the orientation anomaly, a structure model based on displacive modulation of the vernier structure will be proposed in a subsequent paper(12). 4. More evidence has been found that the Nd14zFe4P4(and maybe, also other compounds RI,~Fe4P4) belongs to the infinitely sdapt ive structures(13,14). Although the basic physical picture of the vernier structure with two interpenetrating substructures basically does not change, the substructures can couple to different superstructures(commensurate or incommensurate, tetragonsl or distorted tetragonal symmetry) quasi-continuously within s certain composition range or can relate to other degrees of freedom of the system. The adaptability to the composition can occur possibly by the relative accomodation of two periodicities of the substructures or by a certain form of structural change rather than through the formation o f a solid solution. The variety of EDPs and more detailed discussion will be given in ref. 15. Summary The ~DPs of NdI~£FedB 4 reveal the variety of the crystal structure. The observatlons indic,re that there exists a quasi-continuous series of compounds near the composition Nd1.1Fe4P 4. Such characteristics can be explained ~n terms of the small energy differences between these phases. The coexistence of different phases in the same bulk sample may be related to local fluctuations of the composition. Clarification of structural details can be expected from more precise electron microscopy studies. References I. 2. 5. 4. ~. 6. 7. 8. 9. ~0. 11. 12. 13. 14. 15.
M. Sagawa, S. ~%/jimura, N.Togawa, H.Yamamoto And V.Mstsuura, J. ApDI. Phys. 55, 2085(~984). D.Oivord, J.M.Moresu and P.Tenaud, ~ol. ~ta. Commun. 55, 505(1985). A.Bezinge, ~.V.~raun, J.~lller and K.Yvon, ibid. 55, 151(1985). D.Nisrchos, O.Zou~anelis, A.~ostikas and A.Slmopoulos, ibid. 59, 589(1986). H.Q.Rechenberg, A.Padu, n-Vilho and F.P.Missell, ibid. 59, 541(Iq86). D.~ivord, £.Tenaud and J.M.Moreau, J. Less-Common Metals, 123, 109(1986). D.Givord, P.Tenaud and J.M.Moreau, J. Less-Common Metals, 11~, L7(1986). Zhso Zhibo, Ms Ruzhang and Pan ShuminF, Acts Metallurgics, (~989) ~n press. O. Echwomma, H. Nowotny and A.Wittmann, Monatshefte f~Ir Chem. 94, 681(1963). W. Jeitschko and F.Parthd, Acts Cryst. 22, 4~7(1967). J. Rpyridelis, P.Delsvi~nette and £.Amel~nckx, Phys. Sta. Sol. 19, 685(1967). Zhao Zhibo, ×is Sike, Ma Ruzhang, Ping Jueyun, Miao Baihe and Pan Shuming, £oI. ~ts. Commun. in press. J.S.Anderson, J. Chem. £oc., Dalton, 1107(1973). J.S.Anderson, J. de Physique, 38, Col]oque 7, 17(~977). Zhao Zhibo, Xia Sike, WAn~ Cairong and Ma Ruzhang, J. Phys.:Condensed Matter, submitted.
746
Nd-Fe-B COMPOUNDS
Vol. 23, No. 5
@--
/
1100
•
!
221
_•
221
2000
oTo @
21 z e_
0 ~)
•
020
1f00
221
Fig. 1:the (001)* pattern of NdI+EFe4B 4.
oIo
~ I1
•
•
020
~'~1
Fig.2:the (102)* pattern of Fe-B substructure, three indices are adopted for simplicity.
Fig.3:an example of (100)* pattern of Nd.+£Fe4B4, the basic reflection~ are indexed corresponding to two substructures, respectively.
ol,,,To a
o~T oooo
w
o-~o
oi_2o ,m
_ . ~ o~o h
ol~!
~
oo.Zoooo2
©
oToT 0
0-~00~
wO'--
oTo1 (D
oT2o "
--
8 IO 12 14 18 18 20
--::-''-¢o
Fig.4:the illustration of the predicted (100)* pattern,G:the basic reflections of Nd substructure,O:the basic reflections of the Fe-B substructure, ~):the basic reflections due to the common contribution of two substructures, @ :the satellites of superlattice spots. (a): the basic pattern of the (1OO)* pattern.(b):the EDP of the idealied superstructure NdIo(Fe4B4)9.
OO2O0002
01 O1
oT20
Fig.5:the (T~)* (here referring t o t h e Fe-B s u b s t r u c t u r e ) pattern showing the orientation anomaly.
THE ELECTRON
Vol. 23, pp. 743-746, 1989 Printed in the U.S.A.
DIFFRACTION
PATTERNS(EDPS)
Pergamon Press plc All rights reserved
OF NdI+£Fe4B 4 COMPOUNDS
Zhao Zhibo* Ma Ruzhang* Miao Baihe** *:Department of Materials Physics, Beijing University of Science ann Technology, Beijing, P. R. China. *~:Department of Material Science and Engineering, Beijing University of Science and Technology, Beijing, P. R. China. (Received February 3, 1988) (Revised February 24, 1989) ~ntroduction The promising permanent magnet Nd-Fe-B was elaborated on by Sagawa et al in 1983(I). The existence and the unique crystal structure o£ the so calle0 boronrich phase have been described recently (2,3). The results of composition analysis and the structure refinements indicate that the chemical formula of the boron -rich phase in Nd-Fe-B system should be written as N d I ~ F e 4 B 4 ( ~ = 0 . 1 ) . similar structural properties can occur if Nd is replaced by Other rare earth elements. It is well known that more and more incommensurate modulated crystal structures are being found in nature, but less frequent are the so called incommensurate composite crystal structures which are composed of two or more mutuallj incommensurate subsystems. The RI~¢Fe4B4(R represents rare earth elements) serie s may belong to this type of com~6~nd. X-ray diffraction studies and MGssbauer investigations on some members of the series of the R. - F ~ B 4 compounds have been reported by several authors(2-8). The purpose of our ~8~k is to investigate the Ndx~fFe4B 4 compounds as an example of this series by means of a transmission electro~-~icroscope,which can overcome the inhomogeneity of the bulk samples and reflect nonstatistical information of NdI+~Fe4B4 crystals. According to the results of X-ray diffraction, the crystal structures of the compounds R , ~ F e 4 B 4 can all be divided into two interpenetratin~ substructures: R s u b s t r u c t u r @ ~ a n d Fe-B substructures: both have tetragonal symmetry. In the R substructures, R atoms form the linear strings along the ~ direction at (I/4,3/4) and (3/4,1/4) posltionS. Iron atoms build the chains of edge-sharing tetraheara parallel to the ~ axis, centered at (I/4,1/4) ano (3/4,3/4)- The boron atoms are filled inside the channels in the form of pairs, which connect the R chains and the framework formed by iron tetrahedra. Two substructures have the same tetragonal basal plane and the lattice parameters are about a=0.705-0.716 nm(3). The most interesting feature is that they have different periods in the ~ direction. Such characteristics hence give them the names vernier ~tructure@ or chimne2l@dder ~tructures. They were originally found to exist in Mn-si alloys and other related systems(9,10), since the value of c(Fe-B)/c(R), (c(Fe-B)=0.390-O.392 nm and c(R)=0.341-0.353 nm(3)) , can not be expressed by the ratio of two relatively small integers, the crystal structures of the compounds are either incommensurate or have an unusually long period in the ~ direction. Whether or not the commensurate long period superstructure exists can not be determined from the resolution of the presently available X-ray diffraction data. One can of course always find two integers m and n, within a specified tolerance, to meet the need of m/n= c(Fe-B)/c(R) and hence, the commensurate models with the formulae Rm(Fe4B4)" can be constructed although their physical justification is still questionable. The crystal structures of the R , + ~ F e 4 ~ compounds for R=Nd,Sm and Gd have been refined under the commensuratd models w i t h the chemical formulae NdsFe18B18(i.e. NdIo(Fe4B4)9), Sm77(Fe4B4)Isand Gds(Fe4B4)z , respectivel~. In all cases, the modulation of iron tetrahedra was observed.
743 0036-9748/89 $3.00 + .00 Copyright (c) 1989 Pergamon Press plc
744
Nd-Fe-B COMPOUNDS
Vol. 23, No. 5
Experimental Procedure Alloys with nominal compositions around Nd I iFe4 ~ were prepared by induction melting of pure Nd, Fe and the compacted amor~hdus boron constituents. The ingots were sealed in evacuated quartz tubes and annealed at 1300 K for 40 days. X-ray and M~ssbauer investigations have shown that these samples mainly consist of the ternary compounds NdI~£Fe4B 4 and a small amount of impurity phases(8). For the preparation of the TEM specimen, the ingots were crushed into small fragments. They were dispersed in ethyl alcohol and collected on a carbon-coated,perforated plastic film supported by a copper mesh of 3 mm diameter. Suitable fragments were selected for observation on the H-800 TEM at the operating voltage 200 kV. Results and Simple InterPretation The reflections in the EDPs of the compounds NdI.~Fe4B 4 can be classified into three species: the basic reflections of the Fe-B sd~structure, the basic reflections of the Nd substructure and the superlattice spots, i.e. the satellites due to the interaction(coupling) between two substructures. It can be observed that the satellites appear only in the cases that the electron beam is perpendicular to the ~ axis, which indicates that the long period (even incommensurate) modulation only exists in the ~ direction. Four indices(hkl112) are adopted to index the basic reflections in view of the characteristics of the double-periodicity in this system. Since the Fe-B substructure and the Nd substructure have the same tstragonal basal plane, the (hkO0) reflections are attributed to the whole crystal structure, i.e. both Fe-B substructure and Nd substructure. We suppose that the indices (hkl10) and (hkOl2) represent the basic reflections due to the Fe-B sublattice and the Nd sublattlce, respectively. The EDPs of the N d .+. F e 4 B 4 exhibit variety with respect to the results of X-ray diffraction. No u n ~ e relation exists between the observed phases and the nominal composition of the prepared samples. Although showing clear similarities for same zones, the slight different characteristics of the diffraction patterns can be observed in alloys whose compositions are around Ndl ~Fe4B4, even in the same bulk samples, which implies that the samples are very in~G~ogeneous, even after a long period of annealing treatment. Here the crystals exhibiting distinctive features of the EDPs are defined as different phases of NdI+£Fe4B 4 compounds. I. The (001)* pattern is given in Fig. 1. It can be found that the reflections (hkO0) appear only for h+k=2n (n an integer). The extinction rule reveals that there is a concealed diagonal glide plane along the 4-fold axis, which is in accord with the space groups of the Fe-B substructure(P42/ncm) and of the Nd substructure(I4/mmm) simultaneously. Fig.2 is the diffraction pattern(102)* which is attributed to the Fe-B substructure alone. In this EDP, the (010),(030) etc. reflections which violate the extinction rules in the space group P42/ncm appear. we propose that this can be explained by a double diffraction effect. One of the possible combinations of the pairs of diffraction vecters is shown in the illustration of Fig.2. It can be noted that both (001)* and (I02)F~4 are all formed by the basic reflections of Nd~+#Fe4B 4 compounds. No remarkable changes of such ba sic patterns i.e. patterns f6~led only by the basic reflections, can be observed for different phases of the NdI+~Fe4B 4 compounds. 2.Another type of basic pattern in the (uvO)* sections alsqodoes not change between the different N d ~ f F ~ B 4 compounds(e.g, see Fig.4(a))?~This type of basic pattern with which the (G~B)* sections are indexed is only a ~art of a whole (uvO)* pattern.Each basic reflection can be attributed to either the Fe-B substructure, or the Nd substructure, or to both of them. The basic patterns, however, can not give information about the superstructures coupled by two substructures. The most typical and useful EDPs are the (uvO)* sections, in which a variety of characteristics, due to the appearances of the satellites, can be found. The (100)* pattern of one fragment of the Nd~ IFe4B4 alloy is given in Fig.3 and the basic reflections are indexed according ~6 Fig.4(a). The satellites are arran&ed as chains along the ~ direction. Their intensity distribution is irregular possibly due to both the intrinsic structural properties of the vernier structure and the dynamical effect of electron diffraction. Let us consider an idealized vernier structure in which a perfect long period ordering is supposed to exist and other
Vol.
23, No.
5
Nd-Fe-B
COMPOUNDS
745
deflects are also neglected. The ('ist~ibution of the satellites is decided by periodicity(if any) of the superstructure. Further considering the Ndl0(FedP4)9 phase whose crystal structure has been refined in the supercell with c=10c(Nd)=9c(Fe-B), we can get the diffraction pattern shown in ~ig.4(b) subsequent to Fig.4(a). It can be seen that ~t is in accord with the (~O0)~ pattern in Fig. 3, qualitatively; it seems to us that the commensurate model adopted in the X-ray structure analysis (2) is reasonable. Two unexpected strong spots, however, are observed at satellite positions indicated by the arrows in Fig.3. No presently available structural knowledge of the vernier stm~cture can give an interpretation of these. We propose that the unexpected strong intensity originates in double diffraction in which very strong spots, i.e., the Nd basic reflections (0101),(0~01),(010~) snd (0~0~), are involved. The illustration is shown in Fig.4(b) by the parallelogram. 3. The most interesting type of (uvO)* section can be found occasionally. A typical example is shown in Fig. 5. With reference to the Fe-B substructure, it is indexed as the (~30)* zone. It can be observed that rows of closely s p a c e d ~ p o t s around the Fe-B basic reflections are clearly misorlented relative to the cFe.s direction. This kind of characteristic does not change as the specimen is slightly tilted with respect to the incident electron beam, which implies that the inclination of the spot rows is really related to a unique aspect of the structural properties of the selected cryst~l. The enclosed angles are somewhat variable for different selected fragments exhibiting similar effect. Here we name this phenomenon the orientation snomal~; ,n analogous situation has been found to exist in the tantalum and niobium pentoxlde systems(t1). The X-ray diffraction results on NdI+~Ve4P4(2) fsil to give an explanation of this kind of diffraction pattern. ~or understanding of the orientation anomaly, a structure model based on displacive modulation of the vernier structure will be proposed in a subsequent paper(12). 4. More evidence has been found that the Nd14zFe4P4(and maybe, also other compounds RI,~Fe4P4) belongs to the infinitely sdapt ive structures(13,14). Although the basic physical picture of the vernier structure with two interpenetrating substructures basically does not change, the substructures can couple to different superstructures(commensurate or incommensurate, tetragonsl or distorted tetragonal symmetry) quasi-continuously within s certain composition range or can relate to other degrees of freedom of the system. The adaptability to the composition can occur possibly by the relative accomodation of two periodicities of the substructures or by a certain form of structural change rather than through the formation o f a solid solution. The variety of EDPs and more detailed discussion will be given in ref. 15. Summary The ~DPs of NdI~£FedB 4 reveal the variety of the crystal structure. The observatlons indic,re that there exists a quasi-continuous series of compounds near the composition Nd1.1Fe4P 4. Such characteristics can be explained ~n terms of the small energy differences between these phases. The coexistence of different phases in the same bulk sample may be related to local fluctuations of the composition. Clarification of structural details can be expected from more precise electron microscopy studies. References I. 2. 5. 4. ~. 6. 7. 8. 9. ~0. 11. 12. 13. 14. 15.
M. Sagawa, S. ~%/jimura, N.Togawa, H.Yamamoto And V.Mstsuura, J. ApDI. Phys. 55, 2085(~984). D.Oivord, J.M.Moresu and P.Tenaud, ~ol. ~ta. Commun. 55, 505(1985). A.Bezinge, ~.V.~raun, J.~lller and K.Yvon, ibid. 55, 151(1985). D.Nisrchos, O.Zou~anelis, A.~ostikas and A.Slmopoulos, ibid. 59, 589(1986). H.Q.Rechenberg, A.Padu, n-Vilho and F.P.Missell, ibid. 59, 541(Iq86). D.~ivord, £.Tenaud and J.M.Moreau, J. Less-Common Metals, 123, 109(1986). D.Givord, P.Tenaud and J.M.Moreau, J. Less-Common Metals, 11~, L7(1986). Zhso Zhibo, Ms Ruzhang and Pan ShuminF, Acts Metallurgics, (~989) ~n press. O. Echwomma, H. Nowotny and A.Wittmann, Monatshefte f~Ir Chem. 94, 681(1963). W. Jeitschko and F.Parthd, Acts Cryst. 22, 4~7(1967). J. Rpyridelis, P.Delsvi~nette and £.Amel~nckx, Phys. Sta. Sol. 19, 685(1967). Zhao Zhibo, ×is Sike, Ma Ruzhang, Ping Jueyun, Miao Baihe and Pan Shuming, £oI. ~ts. Commun. in press. J.S.Anderson, J. Chem. £oc., Dalton, 1107(1973). J.S.Anderson, J. de Physique, 38, Col]oque 7, 17(~977). Zhao Zhibo, Xia Sike, WAn~ Cairong and Ma Ruzhang, J. Phys.:Condensed Matter, submitted.
746
Nd-Fe-B COMPOUNDS
Vol. 23, No. 5
@--
/
1100
•
!
221
_•
221
2000
oTo @
21 z e_
0 ~)
•
020
1f00
221
Fig. 1:the (001)* pattern of NdI+EFe4B 4.
oIo
~ I1
•
•
020
~'~1
Fig.2:the (102)* pattern of Fe-B substructure, three indices are adopted for simplicity.
Fig.3:an example of (100)* pattern of Nd.+£Fe4B4, the basic reflection~ are indexed corresponding to two substructures, respectively.
ol,,,To a
o~T oooo
w
o-~o
oi_2o ,m
_ . ~ o~o h
ol~!
~
oo.Zoooo2
©
oToT 0
0-~00~
wO'--
oTo1 (D
oT2o "
--
8 IO 12 14 18 18 20
--::-''-¢o
Fig.4:the illustration of the predicted (100)* pattern,G:the basic reflections of Nd substructure,O:the basic reflections of the Fe-B substructure, ~):the basic reflections due to the common contribution of two substructures, @ :the satellites of superlattice spots. (a): the basic pattern of the (1OO)* pattern.(b):the EDP of the idealied superstructure NdIo(Fe4B4)9.
OO2O0002
01 O1
oT20
Fig.5:the (T~)* (here referring t o t h e Fe-B s u b s t r u c t u r e ) pattern showing the orientation anomaly.