Interaction between C₆₀ and gases under pressure

A brief review is given of the interaction between fullerite C₆₀ and various gases under elevated pressure. Subjects discussed include the formation of ordered interstitial gas-fullerene compounds, reactions between intercalated gases and fullerene molecules to form new endohedral and exohedral comp...

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Datum:	2003
1. Verfasser:	Sundqvist, B.
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Veröffentlicht:	Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України 2003
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spelling	irk-123456789-1288512018-01-15T03:03:14Z Interaction between C₆₀ and gases under pressure Sundqvist, B. Динамика кристаллической решетки A brief review is given of the interaction between fullerite C₆₀ and various gases under elevated pressure. Subjects discussed include the formation of ordered interstitial gas-fullerene compounds, reactions between intercalated gases and fullerene molecules to form new endohedral and exohedral compounds, and changes in the structure and properties of C₆₀ because of intercalated gas atoms or molecules. 2003 Article Interaction between C₆₀ and gases under pressure / B. Sundqvist // Физика низких температур. — 2003. — Т. 29, № 5. — С. 590-596. — Бібліогр.: 36 назв. — англ. 0132-6414 PACS: 61.48.+c, 62.50.+p, 81.05.Tp, 61.72.Ww http://dspace.nbuv.gov.ua/handle/123456789/128851 en Физика низких температур Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України
institution	Digital Library of Periodicals of National Academy of Sciences of Ukraine
collection	DSpace DC
language	English
topic	Динамика кристаллической решетки Динамика кристаллической решетки
spellingShingle	Динамика кристаллической решетки Динамика кристаллической решетки Sundqvist, B. Interaction between C₆₀ and gases under pressure Физика низких температур
description	A brief review is given of the interaction between fullerite C₆₀ and various gases under elevated pressure. Subjects discussed include the formation of ordered interstitial gas-fullerene compounds, reactions between intercalated gases and fullerene molecules to form new endohedral and exohedral compounds, and changes in the structure and properties of C₆₀ because of intercalated gas atoms or molecules.
format	Article
author	Sundqvist, B.
author_facet	Sundqvist, B.
author_sort	Sundqvist, B.
title	Interaction between C₆₀ and gases under pressure
title_short	Interaction between C₆₀ and gases under pressure
title_full	Interaction between C₆₀ and gases under pressure
title_fullStr	Interaction between C₆₀ and gases under pressure
title_full_unstemmed	Interaction between C₆₀ and gases under pressure
title_sort	interaction between c₆₀ and gases under pressure
publisher	Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України
publishDate	2003
topic_facet	Динамика кристаллической решетки
url	http://dspace.nbuv.gov.ua/handle/123456789/128851
citation_txt	Interaction between C₆₀ and gases under pressure / B. Sundqvist // Физика низких температур. — 2003. — Т. 29, № 5. — С. 590-596. — Бібліогр.: 36 назв. — англ.
series	Физика низких температур
work_keys_str_mv	AT sundqvistb interactionbetweenc60andgasesunderpressure
first_indexed	2025-07-09T10:02:10Z
last_indexed	2025-07-09T10:02:10Z
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fulltext	Fizika Nizkikh Temperatur, 2003, v. 29, No. 5, p. 590–596 Interaction between C60 and gases under pressure B. Sundqvist Department of Physics, Umea University, S-90187 Umea, Sweden E-mail: bertil.sundqvist@physics.umu.se Received December 2, 2002 A brief review is given of the interaction between fullerite C60 and various gases under elevated pressure. Subjects discussed include the formation of ordered interstitial gas–fullerene com- pounds, reactions between intercalated gases and fullerene molecules to form new endohedral and exohedral compounds, and changes in the structure and properties of C60 because of intercalated gas atoms or molecules. PACS: 61.48.+c, 62.50.+p, 81.05.Tp, 61.72.Ww Introduction Solid fullerites, such as C60 and C70, have very in- teresting physical properties. However, in many cases the understanding of these properties has been hin- dered or delayed because interactions between the fullerene molecules and their environment have led to significant changes. Although the fullerene molecule is not very reactive, the intermolecular interactions are very weak and many simple properties change eas- ily when the fullerite lattice is structurally deformed, or when small amounts of impurities are introduced. A particular case in point is the study of fullerites under high pressure [1,2]. Pressure is a very useful pa- rameter in the study of carbon-based materials. Al- though the graphite sheet structure has a higher inter- atomic binding energy than diamond, the weak interplane interaction in the three-dimensional gra- phite lattice implies that graphite is easily deformed by moderate pressures, and the equilibrium pressure between diamond and graphite at room temperature is only about 2 GPa [3]. Similarly, carbon nanotubes in bundles begin deforming radially at similar pressures, about 1.7 GPa [4,5]. Although fullerene molecules do not deform noticeably under these pressures, their ori- entation and rotation properties change radically with pressure in the range below 2 GPa [1], and many stu- dies have been carried out to map these changes as functions of pressure p and temperature T. Because C60 and other fullerenes are «weak», easi- ly deformable solids, it is important to use a pressure transmitting medium which does not cause a large shear stress in the specimens studied. This is most eas- ily done using fluid media. However, most fluids that are in the liquid state at room temperature have a rather limited pressure and temperature range before they either crystallize or vitrify into the solid state (at low T or high p), begin breaking down (pyrolyze), or react with the sample material, both usually at high T. In many cases, gases, such as the rare gases, are there- fore considered the «ideal» pressure media. Unfortu- nately, gases often strongly change the properties of fullerites by intercalating into the large interstitials in the lattice. In this paper I briefly review the interaction of gases with C60, and the changes brought about in the properties of C60 when the material has interacted with the gas. The review is mainly motivated by my own need to understand the interactions between fullerites and pressure media, and will be colored by this background, but the subject is also an interesting field of study in itself. The subject has been included before as part of larger reviews [1,6], but since this was some time ago, new material will be presented here. First, a very short introduction is given to the structure of pure C60. This is followed by a review of how solid C60 interacts with various kinds of gases by intercalation, chemical reactions, and the formation of endohedral compounds. Background: the orientational structure of C60 The structure of C60 has been very well discussed in the literature [7,8], and only a brief overview will be given here. At low pressures, C60 has three structurally different phases which, however, are all very similar. © B. Sundqvist, 2003 The room-temperature structure can be described as face-centered cubic (fcc). Both the molecules and the interstitial spaces in the lattice are relatively large, compared to most inorganic atoms or molecules. For each C60 molecule in the lattice there are three inter- stitial sites: two small tetragonal sites with an effec- tive radius of 1.1 Å and one large octahedral site with a radius of 2.1 Å. For comparison, the thresholds or channels between sites have an effective radius of 0.7 Å. Above T0 = 260 K, the C60 molecules carry out quasi-free rotation because of their highly symmetrical shape, and thus the structure can be approximated as a fcc lattice of spherical molecules with a space group Fm m3 . With decreasing T the correlation between the rotation of neighboring molecules increases, and near Tc large, co-rotating clusters are formed. On cooling through T0 the molecular rotation stops and a simple cubic (sc) phase with space group Pa3 and a tempera- ture-dependent degree of orientational order is formed. In this phase the molecular rotation has stopped but the molecules can still jump between dif- ferent molecular orientations. Finally, below the glassy crystal transition at Tg � 90 K, molecular mo- tion is very slow and the remaining orientational dis- order can be considered frozen; an orientational glass is formed. With increasing pressure both T0 and Tg in- crease, as might be expected. The phase lines have slopes of dT0/dp = 160 K·GPa–1 and dTg/dp = = 62 K·GPa–1, respectively [1], and on compression of C60 at room temperature the fcc–sc (or «rotational») transition occurs already near 0.2 GPa. In practice, al- most all high pressure studies are thus carried out on sc (rotationally hindered) C60. In spite of its high symmetry the C60 molecule can be orientationally ordered because it must have 12 car- bon atom pentagons, in addition to the «normal» hexagons, in order to have a closed surface. This gives an anisotropic surface charge distribution and thus an electrostatic driving force for orientation. The two possible orientational states will here be denoted de- scriptively as the P (pentagon) and H (hexagon) ori- entations, since they correspond to the orientation of a double bond on one molecule towards the center of a pentagon or a hexagon, respectively, on a neighboring molecule [7,8]. At atmospheric pressure the energy difference between these states is only about 12 meV, with the P orientation being lower in energy, but com- pression of the lattice shifts this energy difference so that at 150 K the two orientations have the same en- ergy near 0.19 GPa [9]. However, the energy thresh- old for reorientation between these states is quite high, and at atmospheric pressure no orientationally ordered state exists in pure C60. When the material is cooled to below T0 the orientational order improves with decreasing T, but the glass transition intervenes at about 90 K, when the fraction of P-oriented mole- cules is still only about 85%. At sufficiently high pres- sures, however, a completely H-ordered phase should exist. The evolution of orientational order in the pres- sure-temperature phase diagram of molecular C60 is shown in Fig. 1. This figure shows the fcc–sc phase line and the glass transition line as solid lines. In the fcc phase there is no orientational order, and in the low-T «orientational glass» the orientational struc- ture (i.e., the average number of P- and H-oriented molecules) will be frozen at the particular value pres- ent when the sample was cooled through the glass transition line. In the intermediate simple cubic phase, the approximate equilibrium fraction of H-ori- ented molecules is indicated by several (dotted) lines, corresponding to orientational states with 30, 50, 75 and 90% H-oriented molecules. In the simplest possi- ble model the fraction of H-oriented molecules is given by f(T) = [1 + exp (– �/k B T)]–1, (1) where � is the energy difference between the two states. Assuming that � is linear in p and independent of T, f(T,p) will be constant on lines in the p–T plane. The dotted lines in Fig. 1 have been calculated assuming that the two states have equal energies at Interaction between C60 and gases under pressure Fizika Nizkikh Temperatur, 2003, v. 29, No. 5 591 0 0.5 1.0 1.5 400 300 200 100 90% simple cubic «orientational glass» 30% 50% 75% p , GPa T , K fcc (rotationally disordered) Fig. 1. Pressure–temperature phase diagram of pure C60, showing the three structural phases. In the simple cubic range, the orientational structure under various conditions is shown as calculated from Eq. (1). Numbers indicate the fraction of H-oriented molecules along each of the dotted lines shown. 0.19 GPa [9]. (An alternative model, which might be in better agreement with experiment [1], assumes that the energies are always identical at the molecular volume corresponding to 0.19 GPa and 150 K.) Intercalation of C60 with gases Atomic (rare) gases The chemical reactivity of the fullerene molecules is low, and many atomic or molecular species can dif- fuse into the cavities in the fullerite lattice without forming chemical bonds with individual fullerene mo- lecules. As might be expected, there is also a strong correlation between the dimensions of the intercalant atoms or molecules and their ability to intercalate into the interstitial sites in the fullerite lattice. Very care- ful neutron scattering studies of the intercalation of rare gases into these sites have been carried out by Morosin et al.[10,11]. At room temperature they were unable to measure the very high diffusion rate of He, which has an effective atomic radius of 0.93 Å and probably fills all available sites. While He is reported to penetrate the lattice completely within a few mi- nutes, even at quite low applied pressure, Ar, with a radius of 1.54 Å, did not intercalate noticably even af- ter six days at 0.6 GPa. Ne, as expected, is an interme- diate case because of its atomic radius of 1.12 Å, and, as such is an excellent model substance to illustrate the general behavior of many gases. The presence of Ne atoms in the octahedral sites leads to a small ex- pansion of the lattice. Using neutron diffraction, Morosin et al. were able to use this effect to show that Ne diffuses into the lattice with a time constant of a few hours, finally reaching a saturated state in which the Ne occupancy in the octahedral sites was about 20% at atmospheric pressure and increased to about 100% above 0.2 GPa [10]. Interestingly, the rate of Ne diffusion into the C60 lattice depends very strongly on the applied Ne pressure. In the fcc phase the diffusion time constant increases linearly from a few minutes (as for He) at zero pressure to about 90 min at 0.2 GPa, while in the sc phase the time constant for diffusion is approximately 5 h, independent of p over the range studied [11]. It should be noted that while pressure increases the driving force for diffusion, it also decreases the size of the interstitials and channels, but this decrease is much too small to explain the changes in the diffusion rate. On relieving of the Ne pressure, the diffusion of Ne out of the C60 lattice was always very rapid except at very low temperatures (200 K). To explain these observations, Morosin et al. sug- gest that the main transport mechanism for the Ne atoms is a paddlewheel effect [11]. Ne atoms are slightly too large to pass through the «static» chan- nels in the structure, but when the C60 molecules rotate, Ne atoms may follow the movement and be swept in. In particular, it is speculated that Ne atoms may attach to the electron-poor centers of the penta- gons and hexagons, which form dimples or buckets in the molecular structure and which would temporarily afford larger space for atomic transport through the intermolecular channels during rotation. Such a mecha- nism would explain the observation that Ne transport slows down significantly with increasing pressure, which leads to a larger interaction between the C60 molecules and thus to a slowing down of the molecular rotation. In the sc phase, diffusion slows down even more because rotation is replaced by a stepwise, much slower ratcheting movement of the molecules. On re- lief of the external pressure, the presence of Ne atoms in the interstitial sites should result in a larger lattice parameter than normal and thus also a smaller molecu- lar interaction, a more rapid molecular rotation, and a very large diffusion coefficient. The same model should be applicable over a large interval in T, and also to other gases that interact weakly with the fullerene molecules. We would ex- pect the diffusion rate to be high and to increase very strongly with increasing T in the fcc phase (with «free» molecular rotation) and to be smaller and de- crease very rapidly with decreasing T in the sc phase as the orientational ratcheting dies out. These predic- tions agree well with experimental results. At tempe- ratures below 180 K, even He diffusion becomes too slow to be detectable over several hours or days even at 0.5 GPa [12], and at temperatures above 475 K the heavy rare gases (R–Ar, Xe, and Kr) may all diffuse into C60 at 0.17 GPa to form compounds [13] RxC60 with 0.6 < x < 1. After cooling and pressure relief these compounds are stable over long times at room temperature. Although NMR shows that the intermolecular in- teractions and molecular dynamics of intercalated C60 differ little from those of the pristine material, inter- calation into the interstitial sites still changes the lat- tice properties of the material in several subtle ways. In general, the presence of foreign atomic or molecular species in the lattice makes both the central interac- tions between the C60 molecules and the orientational interaction weaker, because intercalation expands the C60 lattice. The effects are particularly large in the case of the heavy rare gases and molecular gases. For KrxC60 and XexC60 this leads to a decrease in T0 from 260 K for pure C60 to 240 K and 200 K, respectively. Compressibility studies on C60 using the (intercalat- ing) lighter rare gases as pressure media showed that the presence of intercalated atoms (He or Ne) made 592 Fizika Nizkikh Temperatur, 2003, v. 29, No. 5 B. Sundqvist the lattice less compressible [14]. However, the fcc–sc transition still occurred at approximately the same molecular volume as for pure C60 (i.e., at a slightly higher pressure), showing that the orientational inter- action had changed little. This was not the case for compounds with the heavy rare gases, for which T0 at atmospheric pressure occurred at a larger molecular volume than for pure C60, indicating a more compli- cated effect on the intermolecular potential. As men- tioned above, the orientational state in the lattice changes with pressure (or, equivalently, volume) in such a way that compression favors the H orientation [1,9]. Conversely, expansion should favour the P ori- entation, and in principle the expanded lattices should have a higher fraction of P-oriented molecules at low T than pure C60. This effect has not been observed in rare gas compounds, but we return to this question be- low. Because intercalation changes the intermolecular interaction it also affects the low-energy vibrations and librations in the lattice, and thus the low-tempe- rature properties. Aleksandrovskii et al. have carried out extensive studies of the low-temperature thermal expansion of C60, which, surprisingly, shows a large negative peak [15] below 4 K. The magnitude of this effect is also very sensitive to the presence of interca- lated gases, even rare gases [16], showing again that intercalation leads to subtle effects in the lattice pro- perties of C60. Molecular gases Many other gases have molecules small enough to diffuse into the C60 lattice, especially under low pres- sures at high temperatures. Many studies have been carried out on the atmospheric components N2 and O2, because of their obvious presence in most practical ex- periments. Other gases that form stable intercalation compounds with C60 are, for example, H2, CH4, CO, CO2, and NO. Gases with relatively large molecules show many interesting effects, when confined to the octahedral interstitial sites in C60. Complete filling of the octahe- dral sites is usually not observed, except for [17] H2 above 75 MPa, but all gases expand the original C60 lattice, and both molecular shape and size are impor- tant in determining the properties of the intercalated material. While the very symmetrical CH4 (or CD4) molecules continue to rotate freely inside the C60 in- terstitial sites [18] even at 210 K, far below the «freezing» temperature T0 for the C60 lattice, the li- near CO2 molecules must be oriented along the <111> directions of the C60 lattice to fit inside the cavities at all, and the interaction between the C60 and the rod-like CO2 molecules induces large structural differ- ences [19] between pure C60 and the intercalated compound at low T. The smaller H2, CO and NO mol- ecules are also free to vibrate and rotate in their cavi- ties. The dynamic behavior of CO has been observed by NMR and IR spectroscopy over large ranges in tem- perature and pressure (or «prison cell» volume), and the interaction between the guest molecules and the C60 host lattice has been analyzed in detail. With a decrease in temperature the motion gradually changes from basically free rotation at room temperature to tunneling between a few orientational states at low temperatures [20], and with an increase in pressure a similar restriction in the motion is observed as the available volume decreases [21]. At the highest pres- sures studied, 3.2 GPa, the molecules must take up oriented positions in the C60 lattice in much the same way as does CO2, and theoretical calculations indicate that the observed spectra agree well with a purely H-oriented C60 lattice. The dynamic behavior of trapped H2 in C60 has also been studied [17]. Studies of the interaction between hydrogen and the carbon atoms in C60 are important from the point of view of understanding fully the interaction of hydrogen with carbon-based storage media, but C60 itself is not a practical storage host since only one H2 molecule can be stored interstitially per C60 molecule, limiting the maximum storage capacity to well below one percent in pure C60. As in the case of heavy rare gases, intercalation of molecular gases leads to significant downward shifts in T0, usually down to 240–250 K, and to large in- creases in the bulk moduli [22]. The lattice expansion should also in principle improve the orientational or- der, as discussed above, and such an effect has indeed been observed in C60 intercalated with CO [23] and NO [24]. For NO, Gu, Tang, and Feng [24] claim to identify a completely pentagon-oriented lattice with T0 = 230 K from dielectric measurements, but no structural evidence is shown. However, a very careful structural study on CO shows [23] a significant en- hancement of the fraction of P-oriented molecules at both intermediate (150 K) and low temperatures. The improved order is believed to arise from a combination of three effects. In addition to the lattice expansion ef- fect already discussed, the glass transition tempera- ture is depressed by about 5 K, and the CO molecules are structurally correlated with the C60 molecules at low T through electrostatic interactions. The dipolar CO molecule prefers to bind weakly to the elec- tron-poor single C–C bonds on P-oriented C60 mole- cules, resulting in an almost completely P-oriented structure. Because of its practical importance, the interaction of C60 with N2 and O2 has received much attention. Interaction between C60 and gases under pressure Fizika Nizkikh Temperatur, 2003, v. 29, No. 5 593 Early NMR studies showed that oxygen diffused re- versibly into the octahedral sites at atmospheric pres- sure and room temperature with equilibrium filling fractions of at most a few percent [25,26]. At high pressures, 10–100 MPa, both O2 and N2 diffuse slowly into the C60 lattice, so that they may fill a large frac- tion of the octahedral sites over a time of several days [27,28]. However, for N2 an elevated temperature (500 K) is needed to reach high filling fractions. Be- cause diffusion is slow (and slower for nitrogen than for oxygen), grain size is important, and finely ground powder reaches the highest filling fractions, while the inner parts of crystallites probably always have a lower filling fraction. Evacuation at slightly elevated temperature (see the next Section) is reported to re- store the C60 to a pure state. The intercalation com- pounds of oxygen have been studied by many me- thods. NMR can give information on the average number of filled octahedral sites [25–27,29] and also shows that the oxygen resides at the center of the in- terstitial sites with no sign of charge transfer or che- mical bonding [26]. Inelastic neutron scattering and Raman scattering also shows that although some vi- bration modes of the intercalated molecules soften ap- preciably when the molecules are confined within the C60 interstitial sites, this has no measurable effect on the vibrational and librational properties of the C60 lattice [28]. In spite of this, calorimetry, structural studies, and dielectric studies [27–29] all show that the rotational transition temperature T0 is strongly depressed by both O2 and N2, by up to –20 K in (O2)xC60 and –22 K in (N2)xC60 [28]. Again, these figures are much larger than can be explained by the intercalation-induced lattice expansion (the «negative pressure effect» [27]). To explain this anomaly, Gu et al. [29] suggest that the local strain set up by diffusing intercalant molecules enhances fluctuations in the or- der parameter close to T0, while Renker et al. [28] suggest that the observed slowing down of molecular motion in the guest molecules transfers energy to the C60 lattice by anharmonic interaction with librational modes, thus reducing the effective height of the en- ergy threshold for molecular rotation. Reactions with intercalated gases As reported above, treatment of intercalated C60 under vacuum usually removes the intercalated gas and restores the material to a pure state. However, this is not true for all gases, and in particular reactions may occur between the C60 and the gas if the tempera- ture is raised. Two gases are particularly likely to re- act, hydrogen and oxygen. Hydrogen easily interca- lates into C60 under pressure, but is also easily desorbed by pumping at room temperature [17]. How- ever, if a high hydrogen pressure is applied to C60 at elevated temperature, a reaction occurs between C60 and intercalated hydrogen, transforming the material into an intercalation compound of H2 in C60Hx. At a pressure of 600 MPa and a temperature of 620 K, x � � 24 has been reported [30]. The intercalated hydro- gen could again be removed by pumping, leaving the new compound behind, and with a long enough reac- tion time the conversion of C60 into hydrofullerite was more or less complete. All forms of carbon, including diamond and fullerites, burn in oxygen at sufficiently high tempera- tures. Although no oxidation of C60 seems to occur at room temperature, measurements at 370 K shows that reactions have occurred and that oxides have formed [31]. At higher temperatures the oxidation increases rapidly. At 470 K strong IR evidence for oxidation is seen, with traces of trapped CO and strong absorption bands from C–O and C=O bonds. The fullerene mole- cules have started breaking down or have been trans- formed into C60Ox. At 570 K, the material breaks down further with the formation of both oxides and amorphous residues from broken cages; in simple terms, it slowly burns. Any fullerite sample exposed to air should thus be kept at temperatures well below 400 K to protect it from permanent changes by oxida- tion. C60 can also react with oxygen without heating. In the discussions above, it has implicitly been assumed that the material has been protected from visible or UV light, since it is well known that both C60 and C70 polymerize if irradiated with such light in an oxy- gen-free environment [32]. Oxygen inhibits this po- lymerization process, but C60 irradiated in the pre- sence of oxygen shows other characteristic changes («photo-transformation») [33,34]. First, radiation with visible or UV light enhances the oxygen diffusion rate in C60 by at least an order of magnitude, so that thin films in air rapidly become oxygen saturated (most oc- tahedral sites filled, at least within the light penetra- tion depth), or oxygen-rich films lose oxygen in a vac- uum. Films (or, equivalently, the surface layers of irradiated bulk material) irradiated for a short time do not differ from the materials discussed above, i.e., the oxygen interacts only weakly with the lattice. After longer times, however, an increasing amount of photo-induced oxidation of C60 to C60Ox becomes evi- dent. After «long time» exposure the films become in- soluble in toluene like photo-polymerized C60, sug- gesting the presence of cross-linked carbon–oxygen clusters in the film. Fullerites should therefore also be protected from light, whether in air, vacuum, or under inert gas. 594 Fizika Nizkikh Temperatur, 2003, v. 29, No. 5 B. Sundqvist Formation of endohedral compounds Fullerenes like C60 and C70 are hollow shells, which can be used as containers for other atoms, and several methods have been found to produce such ma- terials. Here it will only be noted that the formation of such endohedral compounds has been reported dur- ing treatment of fullerenes under reasonably high rare-gas pressure at high temperatures. Saunders et al. [35] reported that under 0.3 GPa at temperatures near 925 K, about 0.1% of the C60 molecules captured rare-gas guest atoms such as He, Ne, Ar, and Kr. The larger Xe molecule, however, did not enter into C60. At high temperatures, C–C bonds on the C60 mole- cules are believed to break spontaneously and the rare-gas atoms then have a chance to enter and get trapped inside when the «window» closes. Endohedral compounds are usually stable for long times under am- bient conditions. The method, the properties of the re- sulting endohedral compounds, and their possible ap- plications have been thoroughly discussed in Ref. 36. Conclusions Intercalation of atomic and molecular gases gives rise to many novel and interesting phenomena in fullerite lattices. Some of these are well understood, while for others our understanding is still only in the early stages. Because intercalation may lead to signifi- cant changes in the properties of fullerite materials both directly and, in some cases, through chemical re- actions induced by temperature or pressure, it is im- portant to understand these effects in order to sort out which properties are intrinsic to C60 or other fullerites and which depend on the presence of intercalated im- purity atoms or molecules. Since intercalation can also be used as a physical tool to study the properties of single molecules or their interactions with carbon or each other, research into intercalation compounds of fullerites will probably continue to be of interest for many years to come. I would like to thank the Swedish Research Coun- cil and the Royal Swedish Academy of Science for funding our work on fullerenes, and Acad. V.G. Manzhelii and Dr. A.N. Aleksandrovskii for discus- sions on the effects of gases trapped in the lattice of C60. 1. B. Sundqvist, Adv. Phys. 48, 1 (1999). 2. V.D. Blank, S.G. Buga, G.A. Dubitsky, N.R. Se- rebryanaya, M.Yu. Popov, and B. Sundqvist, Carbon 36, 319 (1998). 3. F.P. Bundy, W.A. Bassett, M.S. Weathers, R.J. Hem- ley, H.K. Mao, and A.F Goncharov, Carbon 34, 141 (1996). 4. U.D. Venkateswaran, A.M. Rao, E. Richter, M. Me- non, A. Rinzler, R.E. Smalley, and P.C. Eklund, Phys. Rev. B59, 10928 (1999). 5. S. Rols, I.N. Goncharenko, R. Almairac, J.L. Sau- vajol, and I. Mirabeau, Phys. Rev. B64, 153401 (2001). 6. B. Sundqvist, in: Fullerenes: Chemistry, Physics and Technology, K.M. Kadish and R.S. Ruoff (eds.), J. Wiley & Sons, New York (2000), p 611. 7. M.S. Dresselhaus, G. Dresselhaus, and P.C. Eklund, Science of Fullerenes and Carbon Nanotubes, Aca- demic Press, San Diego (1996). 8. P. Launois, S. Ravy, and R. Moret, Int. J. Modern Phys. B13, 253 (1999). 9. W.I.F. David and R.M. Ibberson, J. Phys.: Condens. Matter 5, 7923 (1993). 10. B. Morosin, J.D. Jorgensen, S. Short, G.H. Kwei, and J.E. Schirber, Phys. Rev. B53, 1675 (1996). 11. B. Morosin, Z. Hu, J.D. Jorgensen, S. Short, and G.H. Kwei, Phys. Rev. B59, 6051 (1999). 12. L. Pintschovius, O. Blaschko, G. Krexner, and N. Py- ka, Phys. Rev. B59, 11020 (1999). 13. G. Gadd, S. Moricca, S.J. Kennedy, M.M. Elcombe, P.J. Evans, M. Blackford, D. Cassidy, C.J. Howard, P. Prasad, J.V. Hanna, A. Burchwood, and D. Levy, J. Phys. Chem. Solids 58, 1823 (1997). 14. J.E. Schirber, G.H. Kwei, J.D. Jorgensen, R.L. Hit- terman, and B. Morosin, Phys. Rev. B51, 12014 (1995). 15. A.N. Aleksandrovskii, V.B. Esel’son, V.G. Manzhelii, A. Soldatov, B. Sundqvist, and B.G. Udovidchenko, Fiz. Nizk. Temp. 26, 100 (2000) [Low Temp. Phys. 26, 75 (2000)]. 16. A.N. Aleksandrovskii, V.G. Gavrilko, V.B. Esel’son, V.G. Manzhelii, B.G. Udovidchenko, V.P. Maletskiy, and B. Sundqvist, Fiz. Nizk. Temp. 27, 1401 (2001) [Low Temp. Phys. 27, 1033 (2001)]. 17. S.A. Fitzgerald, T. Yildirim, L.J. Santodonato, D.A. Neumann, J.R.D. Copley, J.J. Rush, and F. Trouw, Phys. Rev. B60, 6439 (1999). 18. B. Morosin, R.A. Assink, R.G. Dunn, T.M. Massis, J.E. Schirber, and G.H. Kwei, Phys. Rev. B56, 13611 (1997). 19. M. James, S.J. Kennedy, M.M. Elcombe, and G.E. Gadd, Phys. Rev. B58, 14780 (1998). 20. I. Holleman, G. von Helden, E.H.T. Olthof, P.J.M. van Bentum, R. Engeln, G.H. Nachtegaal, A.P.M. Kentgens, B.H. Meier, A. van der Avoird, and G. Meijer, Phys. Rev. Lett. 79, 1138 (1997). 21. I. Holleman, G. von Helden, A. van der Avoird, and G. Meijer, Phys. Rev. Lett. 80, 4899 (1998). 22. S. van Smaalen, R.E. Dinnebier, R. Milletich, M. Kunz, I. Holleman, G. von Helden, and G. Meijer, Chem. Phys. Lett. 319, 283 (2000). 23. S. van Smaalen, R.E. Dinnebier, W. Schnelle, I. Hol- leman, G. von Helden, and G. Meijer, Europhys. Lett. 43, 302 (1998). 24. M. Gu, T.B. Tang, and D. Feng, Phys. Rev. B66, 073404 (2002). Interaction between C60 and gases under pressure Fizika Nizkikh Temperatur, 2003, v. 29, No. 5 595 25. R.A. Assink, J.E. Schirber, D.A. Loy, B. Morosin, and G.A. Carlson, J. Mater. Res. 7, 2136 (1992). 26. P. Bernier, I. Luk’yanchuk, Z. Belahmer, M. Ribet, and L. Firlej, Phys. Rev. B53, 7535 (1996). 27. J.E. Schirber, R.A. Assink, G.A. Samara, B. Morosin, and D. Loy, Phys. Rev. B51, 15552 (1995). 28. B. Renker, H. Schober, M.T. Fernandez-Diaz, and R. Heid, Phys. Rev. B61, 13960 (2000). 29. M. Gu, T.B. Tang, C. Hu, and D. Feng, Phys. Rev. B58, 659 (1998). 30. A.I. Kolesnikov, V.E. Antonov, I.O. Bashkin, G. Gros- se, A.P. Moravsky, A.Yu. Muzychka, E.G. Po- nyatovsky, and F.E. Wagner, J. Phys.: Condens. Matter 9, 2831 (1997). 31. M. Wohlers, H. Werner, D. Herein, T. Schedel-Nied- rig, A. Bauer, and R. Schlögl, Synth. Metals 77, 299 (1996). 32. A.M. Rao, P. Zhou, K.-A. Wang, G.T. Hager, J.M. Holden, Y. Wang, W.-T. Lee, X.-X. Bi, P.C. Eklund, D.S. Cornett, M.A. Duncan, and I.J. Amster, Science 259, 955 (1993). 33. P.C. Eklund, A.M. Rao, P. Zhou, Y. Wang, and J.M. Holden, Thin Solid Films 257, 185 (1995). 34. T.L. Makarova, V.I. Sakharov, I.T. Serenkov, and A. Ya. Vul’, Phys. Solid State 41, 497 (1999). 35. M. Saunders, H.A. Jiménez-Vazquez, R.J. Cross, S. Mroczkowski, M.L. Gross, D.E. Giblin, and R.J. Poreda, J. Am. Chem. Soc. 116, 2193 (1994). 36. M. Saunders, R.J. Cross, H.A. Jimenez-Vazquez, R. Shimshi, and A. Khong, Science 271, 1693 (1996). 596 Fizika Nizkikh Temperatur, 2003, v. 29, No. 5 B. Sundqvist

Interaction between C₆₀ and gases under pressure

Institution

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