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Superdense potassium concentration in some graphite intercalation compounds
1657
Letters to the Editor Acknowledgments.
This study was made possible by financial support from the Carbon Research Center (Penn State) and postdoctoral grants for JAM (Spanish Scientific Research Council, CSIC) and MJIG (Ministry of Science and Education of Spain).
12. 13. 14. 15.
REFERENCES I. 2. 3. 4. 5. 6. 7.
8.
9.
IO. I I.
J. W. Patrick
Characterization
Porosity and Applications.
(Ed.),
in
Carbons:
Halsted Press, New York, 1995. __ C. A. Leon y Leon and L. R. Radovic, in Chemistry and Physics of Carbon, Vol. 24. (P. A. Thrower, Ed.), Dekker, New York, 1994, p. 213. J. M. Solar, F. J. Derbyshire, V. H. J. de Beer and L. R. Radovic, J. Cutal. 129, 330 (1991). K. T. Kim, J. S. Chung, K. H. Lee, Y. G. Kim and J. Y. Sung, Carbon 30, 467 (1992). C. Moreno-Castilla, M. A. Ferro-Garcia, J. RiveraUtrilla and J. P. Joly, Energy & Fuels 8, 1233
16. 17. 18. 19. 20. 21. 22.
(1994).
M. C. RomBn-Martinez, D. Cazorla-Amor6s, A. Linares-Solano, C. Salinas-Martinez de Lecea, H. Yamashita and M. Anpo. Carbon 33, 3 (1995). L. R. Radovic and C. Sudhakar, “Carbon as a Catalyst Support” in Introduction to Carbon Technologies (H. Marsh and E. A. Heintz, Eds.). Elsevier Science, 1995, in press. L. R. Radovic, J. I. Ume and A. W. Scaroni, “On Tailoring the Surface Chemistry of Activated Carbons for Their Use in Purification of Aqueous Effluents,” in Fundamentals of Adsorption (M. D.
LeVan, Ed.). Elsevier Science, 1995, in press. J. M. Solar, C. A. Leon y Leon, K. Osseo-Asare and L. R. Radovic, Carbon 28, 369 (1990). G. Newcombe, J. Colloid Interf. Sci. 164, 452 (1994).
J. Economy, K. Foster, A. Andreopoulos Jung, CHEMTECH, October 1992, p. 597.
23. 24.
K. Kinoshita, Phvsicochemical
Carbon: Electrochemical and Proverties. Wilev-Interscience. .
19iS. M. 0. Corapcioglu 569 (1987).
and C. P. Huang, Carbon
25,
C. A.‘ Leon y Leon, A. A. Lizzio and L. R. Radovic, Proc. Int. Carbon Con& Paris, France, 1990, p. 24. G. Newcombe, R. Hayes and M. Drikas, Cofloids
Surfaces A 78. 65 (1993).
C. *A.Leon y i-eon; J. G. Solar, V. Calemma and L. R. Radovic, Carbon 30, 797 (1992). B. Kastening, M. Hahn and J. Kremskiitter, J. Electroanal. Chem. 374. 159 (1994). J. Lyklema, J. Electroar&. &em. i8, 341 (1968). B. Kastenlng and S. Spinzig, J. Electroanal. Chem.
214, 295 (1986).
M. Miiller and B. Kastenlng, J. Electroanal.
374,
149 (1994).
Chem.
J. S. Noh and J. A. Schwarz, J. Colloid Inter5 Sci.
130, 157 (1989). S. Zalac and N. Kallav. . .I. Colloid Interf:a Sci. ~~ 149. 233 (1992). S. K. Verma and P. L. Walker, Jr., Carbon 30, 837 (1992). T. J. Fabish and D. E. Schleifer, Carbon 22, 19 (1984).
25.
J. S. Johnson, Jr., C. G. Westmoreland, F. H. Sweeton, K. A. Kraus, E. D. Hagaman, W. P. Eatherly and H. R. Child, J. Chromatography 354,
26. 27. 28.
J. S. Noh and J. A. Schwarz, Carbon 28, 675 (1990). Y. Otake and R. G. Jenkins. Carbon 31. 109 (19931. P. Vinke, M. van der Eijk, M. Vkrbree, A.6. Voskamp and H. van Bekkum, Carbon 32, 675 (1994). H. Tamon and M. Okazaki, in Fundamentals of Adsorption. (M. Suzuki, Ed.), Kodansha. Tokyo, 1992, p. 663.
23 1 (1986).
29.
and H.
Superdense potassium concentration in some graphite intercalation compounds F. GOUTFER-WURMSER, C. HI?ROLD and P. LAGRANGE Laboratoire de Chimie du Solide Mineral (URA CNRS 158), Universitk Henri Poincart? Nancy I, B.P. 239, 54506 Vandoeuvre-l&-Nancy Cedex, France (Received 29 September 2995; Accepted 2 October 1995)
Key Words - Graphite; potassium; oxygen: intercalation, poly-layered sheets
The discovery in 1926 by Fredenhagen and Cadenbach [I] of the first stage KCs graphite intercalation compound was the departure point for much research work concerning the intercalation of the metallic elements into graphite. In these reactions, the intercalated metals behave as electron donors towards graphite, that is consequently reduced by intercalated species. This charge transfer allows precisely the formation of a lamellar intercalation compound, which exhibits, because of this, an iono-metallic bonding. It is well known that only the more electropositive elements (alkali metals, earth alkaline metals and several lanthanides) are able to intercalate by themselves into graphite [2]. These binary
phases show in all cases that the intercalated sheets are mono-layered metallic planes. For a long time, the first stage KCs binary compound was considered as the phase, whose potassium concentration was the highest, even if Fredenhagen and Cadenbach mentioned the probable existence of a compound corresponding to the KCs chemical formula. For more than 60 years, it has been impossible to again synthesize this original graphite intercalation compound. However, numerous ternary compounds, that have been synthesized essentially during the eighties in our laboratory, contain large amounts of potassium. We
1658
Letters to the Editor
have reported as examples the following compounds [3]: KHo.&, KHgG, KTIrG, KAsa.&, etc. All these ternaries belong to the first stage; but various phases of higher stages and containing the same intercalated sheets have also been obtained. In these ternary compounds, the charge transfer occurs always in the same manner, since the graphene planes are reduced and consequently are transformed into planar macroanions. However, we have to indicate that the intercalated sheets are, for these ternaries, poly-layered (three, four, and even five superimposed metallic planes, according to the cases). By the means of high pressures, the intercalated potassium amount has been largely increased. Indeed, a KC4 compound was synthesized [4]; but this phase is of course not thermodynamically stable under the ambient conditions, and consequently, it is not the KC4 compound, that Fredenhagen and Cadenbach had reported. It has been shown that this binary KC4 phase contains intercalated sheets, that are mono-layered metallic planes, as the ones of the KCs compound : the interplanar distance is the same in both cases (535 pm). But the potassium atoms are of course much closer in KC4 than in KC*. More recently, we have succeeded in our laboratory in preparing some new graphite intercalation compounds, containing very large amounts of potassium with little oxygen. The chemical formulae of these original first stage purple phases are approximately KC3.s00,07 [5]. We observed five different compounds, corresponding to slightly different interplanar distances (a : 840 pm: 0 : 850 pm; y : 860 pm; 6 : 870 pm; E : 890 pm). The easiest phase to synthesize is that denoted p. All these compounds exhibit some intercalated sheets, that are two superimposed metallic planes. These bilayered sheets can only be observed thanks to the presence of an intermediate oxygen plane, even if this oxygen amount is very small (frequently, we describe these phases as quasi-binary compounds). In order to obtain these compounds, the reaction has to be made with liyuid reactive potassium, containing a very small amount of oxygen (less than one atomic percent). Without oxygen, we think it is impossible to obtain these bi-layered metallic sheets; it is likely that Fredenhagen and Cadenbach had worked with some weakly oxidized potassium, when they observed their “KC4” compound instead of the classical KCs. Some new experiments allowed us to synthesize a new first stage purple compound containing even more potassium : it is an original phase, whose potassium concentration is really superdense, since its chemical formula (obtained from crystallographic date) is close to KC3.200.s. with an interplanar distance of 848 pm. The stage of this compound is confirmed by the measurement of the thickness increase of the sample during the intercalation : Aele = 150% leads to a calculated stage of 1.03. We have to underline the fact that the amount of oxygen is very large, so that this phase is a true ternary compound. But at the present time, it appears to be the richest in potassium among the known graphite intercalation compounds. Like the previous quasi-binary two-layered potassium compounds, this new phase is also very stable in the ambient atmosphere. In Fig. 1 is shown the 001 diffraction pattern of this pure phase, which has been synthesized from an HOPG sample by action of weakly oxidized potassium (36O”C, 69 hours). In Fig. 2, the experimental c-axis electronic density profile of the lamellar compound is
I 003
Fig. 1 001 diffraction pattern of the new first stage graphite-potassium-oxygen compound. compared with the one obtained from the proposed model (this model leads to a better fit to the experimental data). These profiles are drawn from the Fourier transforms of the 001 structure factors. As indicated in the model, the intercalated sheets are constituted of two superimposed potassium layers surrounding a central oxygen plane, that is slightly split into two. This original compound contains approximately 2.5 times more potassium than KCs and 1.23 times more than KC+ We have also studied the 2D-arrangement of these intercalated sheets. It can be described by a hexagonal unit cell, which is particularly unusual, since
y.
00
I
Y
Fig. 2 Electronic density profiles of the new first stage graphite-potassium-oxygen compound (solid line: experimental; dashed line: calculated).
1659
Letters to the Editor the value of its a lattice parameter is 426 pm (three. times the value of the carbon-carbon distance in the graphene plane). This 2D unit cell, which is obviously commensurate with the graphitic one (Fig. 3), characterizes the dense arrangement of the Li-planes in the well-known LiC6 binary [6], that contains of course mono-layered intercalated sheets. In our new compound, the presence of two potassium superimposed layers ought to lead consequently to the following chemical formula : KCsO,. The difference that is observed is probably due to the random absence of a few potassium atoms from their crystallographic sites. On the other hand, we have shown (rotating crystal method) that the c lattice parameter of the 3D unit cell is equal to the interplanar distance di, that is to say 848 pm. This result obviously leads us to consider that the c-axis stacking of the compound must be written . ..AaAolA... (A = graphene plane ; cx = intercalated sheet). Consequently, our radiocrystallographic measurements allow us to already know the symmetry and the size of the 3D unit cell of the compound, even though the contents of this cell are not yet established. We now have to carry on this work with the chemical analysis of this phase, in order to determine directly its chemical formula, with a careful crystallographic study, in order to know the positions of the intercalated atoms inside the unit cell, and with a study of various physical properties.
Fig 3 2D hexagonal unit cell of the new first stage graphite-potassium-oxygen compound. REFERENCES 1. 2. 3. 4. 5. 6.
K.Fredenhagen and G.Cadenbach, 2. Anorg. Allgem. Chem. 158,249 (1926). A.HCrold, Mat. SC. Enn. 31. 1 (1977). P.Lagrange, in “Chemical Ph)sics of Intercalation II”, Plenum, New York, (1993) p. 303. V.A. Nalimova, V.V. Avdeev and K.N. Semenenko, Synth. Met. 40, 267 (1991. C. H&old, M. El Gadi, J.F. Mar&he and P. Lagrange, Mol. Cryst. Liq. Cryst. 244, 41 (1994) M. Bagouin, D. Guerard and A. H&old, C. R. Acad. SC. Paris 262, 557 (1966).
Letters to the Editor Acknowledgments.
This study was made possible by financial support from the Carbon Research Center (Penn State) and postdoctoral grants for JAM (Spanish Scientific Research Council, CSIC) and MJIG (Ministry of Science and Education of Spain).
12. 13. 14. 15.
REFERENCES I. 2. 3. 4. 5. 6. 7.
8.
9.
IO. I I.
J. W. Patrick
Characterization
Porosity and Applications.
(Ed.),
in
Carbons:
Halsted Press, New York, 1995. __ C. A. Leon y Leon and L. R. Radovic, in Chemistry and Physics of Carbon, Vol. 24. (P. A. Thrower, Ed.), Dekker, New York, 1994, p. 213. J. M. Solar, F. J. Derbyshire, V. H. J. de Beer and L. R. Radovic, J. Cutal. 129, 330 (1991). K. T. Kim, J. S. Chung, K. H. Lee, Y. G. Kim and J. Y. Sung, Carbon 30, 467 (1992). C. Moreno-Castilla, M. A. Ferro-Garcia, J. RiveraUtrilla and J. P. Joly, Energy & Fuels 8, 1233
16. 17. 18. 19. 20. 21. 22.
(1994).
M. C. RomBn-Martinez, D. Cazorla-Amor6s, A. Linares-Solano, C. Salinas-Martinez de Lecea, H. Yamashita and M. Anpo. Carbon 33, 3 (1995). L. R. Radovic and C. Sudhakar, “Carbon as a Catalyst Support” in Introduction to Carbon Technologies (H. Marsh and E. A. Heintz, Eds.). Elsevier Science, 1995, in press. L. R. Radovic, J. I. Ume and A. W. Scaroni, “On Tailoring the Surface Chemistry of Activated Carbons for Their Use in Purification of Aqueous Effluents,” in Fundamentals of Adsorption (M. D.
LeVan, Ed.). Elsevier Science, 1995, in press. J. M. Solar, C. A. Leon y Leon, K. Osseo-Asare and L. R. Radovic, Carbon 28, 369 (1990). G. Newcombe, J. Colloid Interf. Sci. 164, 452 (1994).
J. Economy, K. Foster, A. Andreopoulos Jung, CHEMTECH, October 1992, p. 597.
23. 24.
K. Kinoshita, Phvsicochemical
Carbon: Electrochemical and Proverties. Wilev-Interscience. .
19iS. M. 0. Corapcioglu 569 (1987).
and C. P. Huang, Carbon
25,
C. A.‘ Leon y Leon, A. A. Lizzio and L. R. Radovic, Proc. Int. Carbon Con& Paris, France, 1990, p. 24. G. Newcombe, R. Hayes and M. Drikas, Cofloids
Surfaces A 78. 65 (1993).
C. *A.Leon y i-eon; J. G. Solar, V. Calemma and L. R. Radovic, Carbon 30, 797 (1992). B. Kastening, M. Hahn and J. Kremskiitter, J. Electroanal. Chem. 374. 159 (1994). J. Lyklema, J. Electroar&. &em. i8, 341 (1968). B. Kastenlng and S. Spinzig, J. Electroanal. Chem.
214, 295 (1986).
M. Miiller and B. Kastenlng, J. Electroanal.
374,
149 (1994).
Chem.
J. S. Noh and J. A. Schwarz, J. Colloid Inter5 Sci.
130, 157 (1989). S. Zalac and N. Kallav. . .I. Colloid Interf:a Sci. ~~ 149. 233 (1992). S. K. Verma and P. L. Walker, Jr., Carbon 30, 837 (1992). T. J. Fabish and D. E. Schleifer, Carbon 22, 19 (1984).
25.
J. S. Johnson, Jr., C. G. Westmoreland, F. H. Sweeton, K. A. Kraus, E. D. Hagaman, W. P. Eatherly and H. R. Child, J. Chromatography 354,
26. 27. 28.
J. S. Noh and J. A. Schwarz, Carbon 28, 675 (1990). Y. Otake and R. G. Jenkins. Carbon 31. 109 (19931. P. Vinke, M. van der Eijk, M. Vkrbree, A.6. Voskamp and H. van Bekkum, Carbon 32, 675 (1994). H. Tamon and M. Okazaki, in Fundamentals of Adsorption. (M. Suzuki, Ed.), Kodansha. Tokyo, 1992, p. 663.
23 1 (1986).
29.
and H.
Superdense potassium concentration in some graphite intercalation compounds F. GOUTFER-WURMSER, C. HI?ROLD and P. LAGRANGE Laboratoire de Chimie du Solide Mineral (URA CNRS 158), Universitk Henri Poincart? Nancy I, B.P. 239, 54506 Vandoeuvre-l&-Nancy Cedex, France (Received 29 September 2995; Accepted 2 October 1995)
Key Words - Graphite; potassium; oxygen: intercalation, poly-layered sheets
The discovery in 1926 by Fredenhagen and Cadenbach [I] of the first stage KCs graphite intercalation compound was the departure point for much research work concerning the intercalation of the metallic elements into graphite. In these reactions, the intercalated metals behave as electron donors towards graphite, that is consequently reduced by intercalated species. This charge transfer allows precisely the formation of a lamellar intercalation compound, which exhibits, because of this, an iono-metallic bonding. It is well known that only the more electropositive elements (alkali metals, earth alkaline metals and several lanthanides) are able to intercalate by themselves into graphite [2]. These binary
phases show in all cases that the intercalated sheets are mono-layered metallic planes. For a long time, the first stage KCs binary compound was considered as the phase, whose potassium concentration was the highest, even if Fredenhagen and Cadenbach mentioned the probable existence of a compound corresponding to the KCs chemical formula. For more than 60 years, it has been impossible to again synthesize this original graphite intercalation compound. However, numerous ternary compounds, that have been synthesized essentially during the eighties in our laboratory, contain large amounts of potassium. We
1658
Letters to the Editor
have reported as examples the following compounds [3]: KHo.&, KHgG, KTIrG, KAsa.&, etc. All these ternaries belong to the first stage; but various phases of higher stages and containing the same intercalated sheets have also been obtained. In these ternary compounds, the charge transfer occurs always in the same manner, since the graphene planes are reduced and consequently are transformed into planar macroanions. However, we have to indicate that the intercalated sheets are, for these ternaries, poly-layered (three, four, and even five superimposed metallic planes, according to the cases). By the means of high pressures, the intercalated potassium amount has been largely increased. Indeed, a KC4 compound was synthesized [4]; but this phase is of course not thermodynamically stable under the ambient conditions, and consequently, it is not the KC4 compound, that Fredenhagen and Cadenbach had reported. It has been shown that this binary KC4 phase contains intercalated sheets, that are mono-layered metallic planes, as the ones of the KCs compound : the interplanar distance is the same in both cases (535 pm). But the potassium atoms are of course much closer in KC4 than in KC*. More recently, we have succeeded in our laboratory in preparing some new graphite intercalation compounds, containing very large amounts of potassium with little oxygen. The chemical formulae of these original first stage purple phases are approximately KC3.s00,07 [5]. We observed five different compounds, corresponding to slightly different interplanar distances (a : 840 pm: 0 : 850 pm; y : 860 pm; 6 : 870 pm; E : 890 pm). The easiest phase to synthesize is that denoted p. All these compounds exhibit some intercalated sheets, that are two superimposed metallic planes. These bilayered sheets can only be observed thanks to the presence of an intermediate oxygen plane, even if this oxygen amount is very small (frequently, we describe these phases as quasi-binary compounds). In order to obtain these compounds, the reaction has to be made with liyuid reactive potassium, containing a very small amount of oxygen (less than one atomic percent). Without oxygen, we think it is impossible to obtain these bi-layered metallic sheets; it is likely that Fredenhagen and Cadenbach had worked with some weakly oxidized potassium, when they observed their “KC4” compound instead of the classical KCs. Some new experiments allowed us to synthesize a new first stage purple compound containing even more potassium : it is an original phase, whose potassium concentration is really superdense, since its chemical formula (obtained from crystallographic date) is close to KC3.200.s. with an interplanar distance of 848 pm. The stage of this compound is confirmed by the measurement of the thickness increase of the sample during the intercalation : Aele = 150% leads to a calculated stage of 1.03. We have to underline the fact that the amount of oxygen is very large, so that this phase is a true ternary compound. But at the present time, it appears to be the richest in potassium among the known graphite intercalation compounds. Like the previous quasi-binary two-layered potassium compounds, this new phase is also very stable in the ambient atmosphere. In Fig. 1 is shown the 001 diffraction pattern of this pure phase, which has been synthesized from an HOPG sample by action of weakly oxidized potassium (36O”C, 69 hours). In Fig. 2, the experimental c-axis electronic density profile of the lamellar compound is
I 003
Fig. 1 001 diffraction pattern of the new first stage graphite-potassium-oxygen compound. compared with the one obtained from the proposed model (this model leads to a better fit to the experimental data). These profiles are drawn from the Fourier transforms of the 001 structure factors. As indicated in the model, the intercalated sheets are constituted of two superimposed potassium layers surrounding a central oxygen plane, that is slightly split into two. This original compound contains approximately 2.5 times more potassium than KCs and 1.23 times more than KC+ We have also studied the 2D-arrangement of these intercalated sheets. It can be described by a hexagonal unit cell, which is particularly unusual, since
y.
00
I
Y
Fig. 2 Electronic density profiles of the new first stage graphite-potassium-oxygen compound (solid line: experimental; dashed line: calculated).
1659
Letters to the Editor the value of its a lattice parameter is 426 pm (three. times the value of the carbon-carbon distance in the graphene plane). This 2D unit cell, which is obviously commensurate with the graphitic one (Fig. 3), characterizes the dense arrangement of the Li-planes in the well-known LiC6 binary [6], that contains of course mono-layered intercalated sheets. In our new compound, the presence of two potassium superimposed layers ought to lead consequently to the following chemical formula : KCsO,. The difference that is observed is probably due to the random absence of a few potassium atoms from their crystallographic sites. On the other hand, we have shown (rotating crystal method) that the c lattice parameter of the 3D unit cell is equal to the interplanar distance di, that is to say 848 pm. This result obviously leads us to consider that the c-axis stacking of the compound must be written . ..AaAolA... (A = graphene plane ; cx = intercalated sheet). Consequently, our radiocrystallographic measurements allow us to already know the symmetry and the size of the 3D unit cell of the compound, even though the contents of this cell are not yet established. We now have to carry on this work with the chemical analysis of this phase, in order to determine directly its chemical formula, with a careful crystallographic study, in order to know the positions of the intercalated atoms inside the unit cell, and with a study of various physical properties.
Fig 3 2D hexagonal unit cell of the new first stage graphite-potassium-oxygen compound. REFERENCES 1. 2. 3. 4. 5. 6.
K.Fredenhagen and G.Cadenbach, 2. Anorg. Allgem. Chem. 158,249 (1926). A.HCrold, Mat. SC. Enn. 31. 1 (1977). P.Lagrange, in “Chemical Ph)sics of Intercalation II”, Plenum, New York, (1993) p. 303. V.A. Nalimova, V.V. Avdeev and K.N. Semenenko, Synth. Met. 40, 267 (1991. C. H&old, M. El Gadi, J.F. Mar&he and P. Lagrange, Mol. Cryst. Liq. Cryst. 244, 41 (1994) M. Bagouin, D. Guerard and A. H&old, C. R. Acad. SC. Paris 262, 557 (1966).