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Boron trichloride graphite intercalation compound studied by selected area electron diffraction and scanning tunneling microscopy
Journal of Physics and Chemistry of Solids 60 (1999) 737–741
Boron trichloride graphite intercalation compound studied by selected area electron diffraction and scanning tunneling microscopy J. Walter*, H. Shioyama Osaka National Research Institute, AIST, MITI, 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577, Japan Received 21 September 1998; accepted 7 December 1998
Abstract Boron trichloride was intercalated from a 1.0 M solution of BCl3 in heptane at 65⬚C. A mixture of a stage-2 and a stage-3 graphite intercalation compound without unreacted graphite was estimated from an X-ray diffraction pattern. A scanning tunneling microscope study showed the occurrence of a Moire´ structure. This pattern can be interpreted as a commensurate supperlattice to the underlying graphene lattice. This hexagonal in-plane structure formed by guest particles shows the following relationship to the pristine graphite lattice as well as to the pristine BCl3 lattice: a(Moire´) 5 × a(graphite) 2 × a(BCl3) 1225 pm. The structure is rotated by 29⬚ ^ 0.3⬚ in respect to the carbon lattice. This surface structure was confirmed by selected area electron diffraction data. 䉷 1999 Elsevier Science Ltd. All rights reserved. Keywords: A. Inorganic compounds; C. Electron diffraction; C. Scanning tunneling microscopy (STM); D. Superlattices
1. Introduction Graphite intercalation compounds (GICs) were widely studied with regard to their physical properties [1,2]. Owing to the high anisotropy in the sample, such compounds can be described as low-dimensional materials. These unique physical properties of GICs are the reason for the high consideration in academic fields. However, a serious problem against technical applications is the low environmental stability of all intercalated carbons. Some good achievements were done during the last few years to enhance the environmental stability of graphite intercalation compounds [3–9]. One method to describe the environmental stability of intercalated materials is to estimate the inplane structure of an as-prepared compound and compare this structure to the pattern determined on environmental aged samples. The in-plane structures of some GICs were studied by diffraction methods, as electron or X-ray diffraction, XRD * Corresponding author. Tel.: ⫹81-727-519-615; fax: ⫹81-727519-622. E-mail address: [email protected] (J. Walter)
(MoCl5-GIC [10], TaCl5-GIC [11], BiCl3-GIC [12]) and by scanning tunneling microscopy, STM (TaCl5-GIC [11], BiCl3-GIC [13], CoCl2-GIC [14], AlCl3-GIC [15] and alkali metal-GICs [16]). In the current work we describe a superlattice which could be observed by selected area electron diffraction (SAED) and either by STM. This structure will be interpreted with regard to the underlying graphite lattice as well as to the lattice of pristine boron trichloride. Boron trichloride can intercalated from the gas phase into graphite, the stage formation of the BCl3-GICs is strongly correlated to the temperature by the synthesis [17].
2. Experimental Highly orientated pyrolytic graphite (HOPG) was used as host material. Graphite slices of 3 × 3 mm sizes were immersed in a 1.0 M solution of boron trichloride in heptane, and the suspension heated to 65⬚C for one day. Scanning tunneling microscope images were obtained with a Nanoscope III from Digital Instruments Inc. The setpoint current varied from 1.5 to 2.75 nA. The bias ranged from 10 to 100 mV. The sample was cleaved along the basal
0022-3697/99/$ - see front matter 䉷 1999 Elsevier Science Ltd. All rights reserved. PII: S0022-369 7(98)00345-X
Fig. 1. XRD pattern of an as-prepared BCl3-GIC; Cu具Ka 典 radiation, 40 kV accelerating voltage, 150 mA anode current, step-size 0.02⬚. A mixture of a stage-2 BCl3-GIC (Ic 1298 ^ 40 pm) and a stage-3 BCl3-GIC (Ic 1633 ^ 60 pm) was obtained, no unreacted graphite was detected.
738 J. Walter, H. Shioyama / Journal of Physics and Chemistry of Solids 60 (1999) 737–741
J. Walter, H. Shioyama / Journal of Physics and Chemistry of Solids 60 (1999) 737–741
739
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J. Walter, H. Shioyama / Journal of Physics and Chemistry of Solids 60 (1999) 737–741
planes to obtain a fresh surface, which was not in contact with the solution before. All measurements were performed on air at room temperature. All images are filtered and Fourier transformed. The handling of the sample in air must be done very quickly; BCl3-GIC is air sensitive. However, the compound is stable for a short time. The prismatic faces of the intercalation compound were sealed with silver paste. This has two advantages for measuring the sample: (i) GICs are highly anisotropic materials, so a better electrical bridge between the basal plane and the sample holder is established. (ii) The silver paste seals the prismatic faces of the host lattice and can act as a barrier against hydrolysis. Intercalation compounds decompose via a hydrolyzing gradient from the prismatic edges to the center of the compound [9]. It is well known that the size of the host lattice can influence the environmental stability of GICs, a large specimen should be used [8]. These two effects enhance slightly the environmental stability of BCl3-GIC. So it was possible to expose the sample for a short time to air to perform the measurements.
3. Results and discussion 3.1. X-ray diffraction measurement An X-ray diffraction pattern of the as-prepared intercalation compound (Fig. 1) gives evidence that BCl3 is intercalated into graphite. A mixture of a stage-2 BCl3-GIC (Ic 1298 ^ 40 pm) and a stage-3 BCl3-GIC (Ic 1633 ^ 60 pm) was obtained, no unreacted graphite could be detected. The broad and unsymmetrical reflections indicate a disordered sample, which is typical for all kinds of layered materials. The guest lattice is also a layered material. Owing to the intercalation process the disorder in the system is increased. The intercalation process was performed many times the sample always showed the huge disorder. XRD pattern of disordered graphite intercalation compounds can show the following unusual behavior [18,19]: • Some reflections of one identity period are sharp and others of the same identity period are broad. • Some (00l) reflections can be shifted and other (00l) reflections do not shift, so for this reason it is possible to calculate different identity periods for the same stage; their standard deviation is high. • The intensity ratios of (00l) reflections from one stage are not constant, and it is possible that weaker reflections
Fig. 3. SAED images of BCl3-GIC, obtained with a magnification of 200 000×, 300 kV accelerating voltage, camera length 2 m. The axis of the host lattice (a*gr) as well as the axis of the guest lattice (a*M) are indicated by large arrows. The a*M-axis is rotated by 29⬚ ^ 0.3⬚ in respect to a*gr-axis. The reflections (are indicated by small arrows) of the host lattice are bright and the reflections of the guest lattice are weak.
are completely absent in XRD pattern of disordered samples. Sometimes not all of the graphite reacted and a graphite (002) reflection could be observed together with (00l) reflections of BCl3-GIC. 3.2. Scanning tunneling microscopy study Fig. 2(a) shows a STM image of BCl3-GIC with a Moire´ pattern. Such a hexagonal in-plane pattern shows an a(Moire´)axis of 1225 pm (see bar inside the STM image). Moire´ pattern occurs when two hexagonal lattices with different a-axis build one common structure. Graphite has a well known hexagonal structure (space group: P63/mmc, a(graphite) 245.4 pm, c(graphite) 670 pm) [20]. Solid boron trichloride shows also a hexagonal lattice (spacegroup P63) with a(BCl3) 614 pm and c(BCl3) 660.6 pm [21]. From the knowledge of these two lattice parameters and both crystal systems, the observed Moire´ pattern can easily be interpreted. Boron trichloride forms a hexagonal in-plane structure in addition to the underlying hexagonal graphite lattice. Owing to the different lattice parameters a Moire´ pattern occurs. The observed Moire´ pattern shows close relationships to the pristine lattice parameter of graphite as well as to the lattice parameter of pristine BCl3.
Fig. 2. (a) STM images of BCl3-GIC. Clearly the carbon lattice and an additional Moire´ pattern can be observed. This superlattice shows an aaxis of 1225 pm (see indicated bar). The a-axis of the superlattice shows a close relationship to the a-axis of pristine graphite and to pristine BCl3: a(Moire´) 5 × a(graphite) 2 × a(BCl3) 1225 pm. (b) Schematic drawing of the Moire´ pattern observed by STM. Hatched circles represented the Moire´ pattern, the pattern formed by lines represented the host lattice. The unit cell of graphite as well as a half unit cell of the Moire´ pattern is indicated, it is a commensurate structure. The Moire´ pattern is rotated by 29⬚ ^ 0.35⬚ in respect to the host lattice. Owing to this rotation a small misfit to the underlying carbon lattice occurs, a(Moire´) 1225 pm, see indicated bar in Fig. 2(a).
J. Walter, H. Shioyama / Journal of Physics and Chemistry of Solids 60 (1999) 737–741
• Experimental • a(Moire´) 2 × a(BCl3) 1225 pm • a(Moire´) 5 × a(graphite) 1225 pm • Theoretical • 2 × a(BCl3) 1228 pm • 5 × a(graphite) 1227 pm The a-axis of the Moire´ pattern is rotated by 29⬚ ^ 0.35⬚ in respect of the a-axis of graphite. Fig. 2(b) shows a schematic drawing of the Moire´ pattern. The unit cell of graphite is indicated as well as a half unit cell of the superlattice. The rotation by 29⬚ in respect to agr is shown. The guest lattice is a commensurate lattice in regard to the host lattice. Owing to the rotation a small misfit results. The rotation of a guest lattice in respect to the host is certainly attributed to the difficulty of incorporation of a layered material in another layered structure.
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graphite is successful. The intercalation could be confirmed by X-ray diffraction, selected area electron diffraction and by scanning tunneling microscopy. In a-direction the lattice parameter of pristine BCl3 is about half of the value determined for intercalated BCl3. The superlattice shows also a close relationship to pristine graphite. In a-direction the lattice parameter of pristine graphite is about a fifth of the value determined for intercalated BCl3; it is a commensurate superlattice which is rotated by 29⬚ ^ 0.3⬚ in respect to the host lattice. Acknowledgements Ju¨rgen Walter is grateful to the Alexander von HumboldtFoundation (AvH, Germany) and the Science and Technology Agency (STA, Japan) for his Japan fellowship.
3.3. Selected area electron diffraction study
References
The in-plane lattice of the as-prepared intercalation compound (Fig. 3) was also investigated by SAED. This pattern was obtained at a magnification of 200 000 × and gives a further evidence for the successful intercalation of boron trichloride in HOPG. Fig. 3 shows the in-plane diffraction pattern with indicated axis of the host lattice (a*gr) and the guest lattice (a*M). Carbon and BCl3 crystallize in a hexagonal system, so the angle between both a*graxis or between both a*M-axis is 60⬚. The guest lattice is rotated by 29⬚ ^ 0.3⬚ in respect to the host lattice. Some reflections of the host as well as of the guest lattice are indicated. The d(100)gr could be used as internal standard and the camera constant could be so refined to 3.93 × 10 ⫺12 m 2.
[1] O. El-Shazly, J. Phys. Chem. Solids 58 (1997) 149. [2] Y.V. Zubavichus, Y.L. Slovokhotov, L.D. Kvacheva, Y.N. Novikov, Physica B 208/209 (1995) 549. [3] J. Walter, H. P. Boehm, Carbon 33 (1995) 1121. [4] J. Walter, M. Maetz, Mikrochim. Acta 127 (1997) 183. [5] J. Walter, Solid State Ionics 101/103 (1997) 833. [6] P. Capkova, D. Rafaja, J. Walter, H.P. Boehm, K.F. van Malssen, H. Schenk, Carbon 33 (1995) 1425. [7] J. Walter, H. Shioyama, Y. Sawada, Carbon 37 (1999) 41. [8] J. Walter, H. Shioyama, Synth. Met. 92 (1998) 91. [9] J. Walter, Synth. Met. 89 (1997) 39. [10] A.W. Syme Johnson, Acta Crystallogr. 9 (1956) 421. [11] J. Walter, H. Shioyama, Y. Sawada, S. Hara, Carbon 36 (1998) 1277. [12] P. Behrens, V. Woebs, K. Jopp, W. Metz, Carbon 26 (1988) 641. [13] J. Walter, H. Shioyama, Y. Sawada, Carbon 36 (1998) 1811. [14] M. Tanaka, W. Mizutani, T. Nakahizu, N. Morita, S. Yamazaki, H. Bando, M. Ono, K. Kujimura, J. Microscopy (Oxford) 152 (1988) 183. [15] N. Ikemiya, E. Shimazu, S. Hara, H. Shioyama, Y. Sawada, Carbon 34 (1996) 277. [16] D. Anselmetti, V. Geiser, D. Bradbeck, G. Overney, R. Wiesendanger, H.J. Gu¨ntherodt, Synth. Met. 38 (1990) 157. [17] A.G. Freeman, J.H. Johnston, Carbon 9 (1971) 667. [18] D. Hohlwein, W. Metz, Z. Kristallogr. 139 (1974) 279. [19] W. Metz, E.J. Schulze, Z. Kristallogr. 142 (1975) 409. [20] R.C. Weast, M.J. Astle (Eds.), Handbook of Chemistry and Physics, 63, CRC Press, Boca Raton, 1982, pp. 208. [21] M.A. Rollier, A. Riva, Gazz. Chim. Ital. 77 (1947) 361.
• • • •
d(hkl)M experimental d(hkl)M theoretical d(200)M 538.4 pm d(200)M 531.7 pm d(400)M 269.2 pm d(400)M 265.9 pm d(900)M 117.7 pm d(900)M 118.2 pm
The lattice parameter a was determined to: aexp 1236 ^ 12 pm (theor.: a 1228 pm). The electron diffraction data confirm the superlattice with regard to their symmetry as well as in regard to the lattice constant. 4. Conclusion The intercalation of BCl3 from a heptane solution into
Boron trichloride graphite intercalation compound studied by selected area electron diffraction and scanning tunneling microscopy J. Walter*, H. Shioyama Osaka National Research Institute, AIST, MITI, 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577, Japan Received 21 September 1998; accepted 7 December 1998
Abstract Boron trichloride was intercalated from a 1.0 M solution of BCl3 in heptane at 65⬚C. A mixture of a stage-2 and a stage-3 graphite intercalation compound without unreacted graphite was estimated from an X-ray diffraction pattern. A scanning tunneling microscope study showed the occurrence of a Moire´ structure. This pattern can be interpreted as a commensurate supperlattice to the underlying graphene lattice. This hexagonal in-plane structure formed by guest particles shows the following relationship to the pristine graphite lattice as well as to the pristine BCl3 lattice: a(Moire´) 5 × a(graphite) 2 × a(BCl3) 1225 pm. The structure is rotated by 29⬚ ^ 0.3⬚ in respect to the carbon lattice. This surface structure was confirmed by selected area electron diffraction data. 䉷 1999 Elsevier Science Ltd. All rights reserved. Keywords: A. Inorganic compounds; C. Electron diffraction; C. Scanning tunneling microscopy (STM); D. Superlattices
1. Introduction Graphite intercalation compounds (GICs) were widely studied with regard to their physical properties [1,2]. Owing to the high anisotropy in the sample, such compounds can be described as low-dimensional materials. These unique physical properties of GICs are the reason for the high consideration in academic fields. However, a serious problem against technical applications is the low environmental stability of all intercalated carbons. Some good achievements were done during the last few years to enhance the environmental stability of graphite intercalation compounds [3–9]. One method to describe the environmental stability of intercalated materials is to estimate the inplane structure of an as-prepared compound and compare this structure to the pattern determined on environmental aged samples. The in-plane structures of some GICs were studied by diffraction methods, as electron or X-ray diffraction, XRD * Corresponding author. Tel.: ⫹81-727-519-615; fax: ⫹81-727519-622. E-mail address: [email protected] (J. Walter)
(MoCl5-GIC [10], TaCl5-GIC [11], BiCl3-GIC [12]) and by scanning tunneling microscopy, STM (TaCl5-GIC [11], BiCl3-GIC [13], CoCl2-GIC [14], AlCl3-GIC [15] and alkali metal-GICs [16]). In the current work we describe a superlattice which could be observed by selected area electron diffraction (SAED) and either by STM. This structure will be interpreted with regard to the underlying graphite lattice as well as to the lattice of pristine boron trichloride. Boron trichloride can intercalated from the gas phase into graphite, the stage formation of the BCl3-GICs is strongly correlated to the temperature by the synthesis [17].
2. Experimental Highly orientated pyrolytic graphite (HOPG) was used as host material. Graphite slices of 3 × 3 mm sizes were immersed in a 1.0 M solution of boron trichloride in heptane, and the suspension heated to 65⬚C for one day. Scanning tunneling microscope images were obtained with a Nanoscope III from Digital Instruments Inc. The setpoint current varied from 1.5 to 2.75 nA. The bias ranged from 10 to 100 mV. The sample was cleaved along the basal
0022-3697/99/$ - see front matter 䉷 1999 Elsevier Science Ltd. All rights reserved. PII: S0022-369 7(98)00345-X
Fig. 1. XRD pattern of an as-prepared BCl3-GIC; Cu具Ka 典 radiation, 40 kV accelerating voltage, 150 mA anode current, step-size 0.02⬚. A mixture of a stage-2 BCl3-GIC (Ic 1298 ^ 40 pm) and a stage-3 BCl3-GIC (Ic 1633 ^ 60 pm) was obtained, no unreacted graphite was detected.
738 J. Walter, H. Shioyama / Journal of Physics and Chemistry of Solids 60 (1999) 737–741
J. Walter, H. Shioyama / Journal of Physics and Chemistry of Solids 60 (1999) 737–741
739
740
J. Walter, H. Shioyama / Journal of Physics and Chemistry of Solids 60 (1999) 737–741
planes to obtain a fresh surface, which was not in contact with the solution before. All measurements were performed on air at room temperature. All images are filtered and Fourier transformed. The handling of the sample in air must be done very quickly; BCl3-GIC is air sensitive. However, the compound is stable for a short time. The prismatic faces of the intercalation compound were sealed with silver paste. This has two advantages for measuring the sample: (i) GICs are highly anisotropic materials, so a better electrical bridge between the basal plane and the sample holder is established. (ii) The silver paste seals the prismatic faces of the host lattice and can act as a barrier against hydrolysis. Intercalation compounds decompose via a hydrolyzing gradient from the prismatic edges to the center of the compound [9]. It is well known that the size of the host lattice can influence the environmental stability of GICs, a large specimen should be used [8]. These two effects enhance slightly the environmental stability of BCl3-GIC. So it was possible to expose the sample for a short time to air to perform the measurements.
3. Results and discussion 3.1. X-ray diffraction measurement An X-ray diffraction pattern of the as-prepared intercalation compound (Fig. 1) gives evidence that BCl3 is intercalated into graphite. A mixture of a stage-2 BCl3-GIC (Ic 1298 ^ 40 pm) and a stage-3 BCl3-GIC (Ic 1633 ^ 60 pm) was obtained, no unreacted graphite could be detected. The broad and unsymmetrical reflections indicate a disordered sample, which is typical for all kinds of layered materials. The guest lattice is also a layered material. Owing to the intercalation process the disorder in the system is increased. The intercalation process was performed many times the sample always showed the huge disorder. XRD pattern of disordered graphite intercalation compounds can show the following unusual behavior [18,19]: • Some reflections of one identity period are sharp and others of the same identity period are broad. • Some (00l) reflections can be shifted and other (00l) reflections do not shift, so for this reason it is possible to calculate different identity periods for the same stage; their standard deviation is high. • The intensity ratios of (00l) reflections from one stage are not constant, and it is possible that weaker reflections
Fig. 3. SAED images of BCl3-GIC, obtained with a magnification of 200 000×, 300 kV accelerating voltage, camera length 2 m. The axis of the host lattice (a*gr) as well as the axis of the guest lattice (a*M) are indicated by large arrows. The a*M-axis is rotated by 29⬚ ^ 0.3⬚ in respect to a*gr-axis. The reflections (are indicated by small arrows) of the host lattice are bright and the reflections of the guest lattice are weak.
are completely absent in XRD pattern of disordered samples. Sometimes not all of the graphite reacted and a graphite (002) reflection could be observed together with (00l) reflections of BCl3-GIC. 3.2. Scanning tunneling microscopy study Fig. 2(a) shows a STM image of BCl3-GIC with a Moire´ pattern. Such a hexagonal in-plane pattern shows an a(Moire´)axis of 1225 pm (see bar inside the STM image). Moire´ pattern occurs when two hexagonal lattices with different a-axis build one common structure. Graphite has a well known hexagonal structure (space group: P63/mmc, a(graphite) 245.4 pm, c(graphite) 670 pm) [20]. Solid boron trichloride shows also a hexagonal lattice (spacegroup P63) with a(BCl3) 614 pm and c(BCl3) 660.6 pm [21]. From the knowledge of these two lattice parameters and both crystal systems, the observed Moire´ pattern can easily be interpreted. Boron trichloride forms a hexagonal in-plane structure in addition to the underlying hexagonal graphite lattice. Owing to the different lattice parameters a Moire´ pattern occurs. The observed Moire´ pattern shows close relationships to the pristine lattice parameter of graphite as well as to the lattice parameter of pristine BCl3.
Fig. 2. (a) STM images of BCl3-GIC. Clearly the carbon lattice and an additional Moire´ pattern can be observed. This superlattice shows an aaxis of 1225 pm (see indicated bar). The a-axis of the superlattice shows a close relationship to the a-axis of pristine graphite and to pristine BCl3: a(Moire´) 5 × a(graphite) 2 × a(BCl3) 1225 pm. (b) Schematic drawing of the Moire´ pattern observed by STM. Hatched circles represented the Moire´ pattern, the pattern formed by lines represented the host lattice. The unit cell of graphite as well as a half unit cell of the Moire´ pattern is indicated, it is a commensurate structure. The Moire´ pattern is rotated by 29⬚ ^ 0.35⬚ in respect to the host lattice. Owing to this rotation a small misfit to the underlying carbon lattice occurs, a(Moire´) 1225 pm, see indicated bar in Fig. 2(a).
J. Walter, H. Shioyama / Journal of Physics and Chemistry of Solids 60 (1999) 737–741
• Experimental • a(Moire´) 2 × a(BCl3) 1225 pm • a(Moire´) 5 × a(graphite) 1225 pm • Theoretical • 2 × a(BCl3) 1228 pm • 5 × a(graphite) 1227 pm The a-axis of the Moire´ pattern is rotated by 29⬚ ^ 0.35⬚ in respect of the a-axis of graphite. Fig. 2(b) shows a schematic drawing of the Moire´ pattern. The unit cell of graphite is indicated as well as a half unit cell of the superlattice. The rotation by 29⬚ in respect to agr is shown. The guest lattice is a commensurate lattice in regard to the host lattice. Owing to the rotation a small misfit results. The rotation of a guest lattice in respect to the host is certainly attributed to the difficulty of incorporation of a layered material in another layered structure.
741
graphite is successful. The intercalation could be confirmed by X-ray diffraction, selected area electron diffraction and by scanning tunneling microscopy. In a-direction the lattice parameter of pristine BCl3 is about half of the value determined for intercalated BCl3. The superlattice shows also a close relationship to pristine graphite. In a-direction the lattice parameter of pristine graphite is about a fifth of the value determined for intercalated BCl3; it is a commensurate superlattice which is rotated by 29⬚ ^ 0.3⬚ in respect to the host lattice. Acknowledgements Ju¨rgen Walter is grateful to the Alexander von HumboldtFoundation (AvH, Germany) and the Science and Technology Agency (STA, Japan) for his Japan fellowship.
3.3. Selected area electron diffraction study
References
The in-plane lattice of the as-prepared intercalation compound (Fig. 3) was also investigated by SAED. This pattern was obtained at a magnification of 200 000 × and gives a further evidence for the successful intercalation of boron trichloride in HOPG. Fig. 3 shows the in-plane diffraction pattern with indicated axis of the host lattice (a*gr) and the guest lattice (a*M). Carbon and BCl3 crystallize in a hexagonal system, so the angle between both a*graxis or between both a*M-axis is 60⬚. The guest lattice is rotated by 29⬚ ^ 0.3⬚ in respect to the host lattice. Some reflections of the host as well as of the guest lattice are indicated. The d(100)gr could be used as internal standard and the camera constant could be so refined to 3.93 × 10 ⫺12 m 2.
[1] O. El-Shazly, J. Phys. Chem. Solids 58 (1997) 149. [2] Y.V. Zubavichus, Y.L. Slovokhotov, L.D. Kvacheva, Y.N. Novikov, Physica B 208/209 (1995) 549. [3] J. Walter, H. P. Boehm, Carbon 33 (1995) 1121. [4] J. Walter, M. Maetz, Mikrochim. Acta 127 (1997) 183. [5] J. Walter, Solid State Ionics 101/103 (1997) 833. [6] P. Capkova, D. Rafaja, J. Walter, H.P. Boehm, K.F. van Malssen, H. Schenk, Carbon 33 (1995) 1425. [7] J. Walter, H. Shioyama, Y. Sawada, Carbon 37 (1999) 41. [8] J. Walter, H. Shioyama, Synth. Met. 92 (1998) 91. [9] J. Walter, Synth. Met. 89 (1997) 39. [10] A.W. Syme Johnson, Acta Crystallogr. 9 (1956) 421. [11] J. Walter, H. Shioyama, Y. Sawada, S. Hara, Carbon 36 (1998) 1277. [12] P. Behrens, V. Woebs, K. Jopp, W. Metz, Carbon 26 (1988) 641. [13] J. Walter, H. Shioyama, Y. Sawada, Carbon 36 (1998) 1811. [14] M. Tanaka, W. Mizutani, T. Nakahizu, N. Morita, S. Yamazaki, H. Bando, M. Ono, K. Kujimura, J. Microscopy (Oxford) 152 (1988) 183. [15] N. Ikemiya, E. Shimazu, S. Hara, H. Shioyama, Y. Sawada, Carbon 34 (1996) 277. [16] D. Anselmetti, V. Geiser, D. Bradbeck, G. Overney, R. Wiesendanger, H.J. Gu¨ntherodt, Synth. Met. 38 (1990) 157. [17] A.G. Freeman, J.H. Johnston, Carbon 9 (1971) 667. [18] D. Hohlwein, W. Metz, Z. Kristallogr. 139 (1974) 279. [19] W. Metz, E.J. Schulze, Z. Kristallogr. 142 (1975) 409. [20] R.C. Weast, M.J. Astle (Eds.), Handbook of Chemistry and Physics, 63, CRC Press, Boca Raton, 1982, pp. 208. [21] M.A. Rollier, A. Riva, Gazz. Chim. Ital. 77 (1947) 361.
• • • •
d(hkl)M experimental d(hkl)M theoretical d(200)M 538.4 pm d(200)M 531.7 pm d(400)M 269.2 pm d(400)M 265.9 pm d(900)M 117.7 pm d(900)M 118.2 pm
The lattice parameter a was determined to: aexp 1236 ^ 12 pm (theor.: a 1228 pm). The electron diffraction data confirm the superlattice with regard to their symmetry as well as in regard to the lattice constant. 4. Conclusion The intercalation of BCl3 from a heptane solution into