Fullerene and fullerites. New modern materials Yu. Ossipyan
To cite this version:
Yu. Ossipyan. Fullerene and fullerites. New modern materials. Journal de Physique IV Proceedings, EDP Sciences, 1994, 04 (C9), pp.C9-51-C9-73. 10.1051/jp4:1994908. jpa-00253468
HAL Id: jpa-00253468 https://hal.archives-ouvertes.fr/jpa-00253468 Submitted on 1 Jan 1994
HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. JOURNAL DE PHYSIQUE IV Colloque C9, supplkment au Journal de Physique HI, Volume 4, novembre 1994
Fullerene and fullerites. New modern materials
Yu.A. Ossipyan Institute of Solid State Physics, Russian Academy of Sciences, 142432 Chernogolovka, Moscow District, Russia
I. Introduction
The discovery of a new form of pure carbon - giant molecules called
fullerenes and subsequelltly of a new crystalline form of carbon - fullerite crystals - has been a full-scale scientific boom over the past few years. Hundreds of
laboratories all over the world are being engaged in synthesizing and studying
fullerenes and fullerites and their derivatives, the number of publications amounts to
two thousand, and the rate and scope of researches goes 011 growing.
This report is not a scientific review and it- is not my aiin to cstablish scientific priorities. This is rather a scientific popular lecture that better fits in with the spirit
of this session. In view of this, not to overburden my report, I shall not make individual references in the text and figures since, to be exact and consistent, the
number of such references must be very large. At the end of rliy lecture I shall give
references to several recent very good reviews devoted to individt~al problenis of
fullerene pliysics and chemistry. 'l'he reatlei. will find tile necessary ~xhrenccsto originals in these reviews.
2. History The existence of giant niolecules of carbon, boron or silicon llas loi~gI)eeri
hypothized. Individual quantum chemical calculations evidenced for thc possibility of
stable AGO, and SO on clusters. 1 know about the results of such calculations
made and published ill Moscow back in late 60s early 70s. Possibly, there wcrc
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jp4:1994908 JOURNAL DE PHYSIQUE IV other similar considerations and calculations, however, the ideas and models contained in them were hypothetical and based 011 general though quite sensible, from the stand point of quantum chemistry, assumptions. It was only in 1985 that Richard Smalley's group at Rice University, Texas in collaboration with Harry ICroto at the University of Sussex, England, reported the result of their experimental studies that vapors formed upon laser vaporization of graphite contained considerable amounts of carbon clusters CGO, which was recognized mass-spectrometrically. Concurrently, W.Kratschmer from the Max Planck Institute for Nuclear
Physics, Heidelberg, Germany ant1 Donaltl I~luffman, University of Arizona, 'l'ucson and their students 1-.Lamb ancl I<.Fostiropoulos were conccrnctl wifh ~~roducinp, ocarbon smoke, by vaporizing a graphite electrode in an arc discharge in order lo model the carbon state in interstellar dust. Their spectroscopic efforts have shown that
12 pentagons and 20 hexagons having the same edge dimensioil close to that of C-C bond in graphite. So, now we know three forms of solid carbon - diamond ifig.2), graphite (fig.3) and fullerite (fig.4). A special interest to studies of physical properties of fullerites was arousctl by pul)licatio~~of the sensational \\rork of the group from AT&T Bell Lab's, who reported an observation of high 'rc (=lot<) superconductivity in fullerite specimens treated in 1)otassiulil vapors. .1. his phenomenon was attributed to the process of potassiunl atoms intcscalatioli inlo lllr crystal lattice interstitial sites of fullcritc, likc it takes place with graphite. I'urtlicl. games with variation of the intercalant's type (of alkali ~netals) resultetl in an increase of .I' up to 301< whic:h, j)rcscntly, is scco~itl only to 'I', values of higll c temperature superco~lductorson the base of copper oxitles.
It should be pointed out that the general idea of the niolecular structure of fullerenes, similar to that of aromatic matcrial.~,has suggested that fullcrc,ncs arid fullerites should be inert, chenlically illactive ~natcrials.'l'liis, however, is ~iotlllc case. It has been demonstratccl that f~~llcrcnescan ~)a~.ticil);~tcin ~luliierouscllcrl~ical reactions with the formation of various clicmical deri\!ativcs of fullercnes, 7'his gave birth to a new broad field of organic clicniistrv \\:hic.ll, untloul)tctlly, is ~c~1.y promising. ,
So, two approaches and, corresponclirlgl,v, t\vo tlit'fcrcnt scientific ficltls call I)(. distinguished in the fullerene a~iclfullerite science:
first approacli is to regard fullcritcs 21s stable fornl;~tionsthat Ict atoms of JOURNAL DE PHYSIQUE IV
small radius - mainly alkali atoms - intercalate into tlieir interstitial positions. In this case the chemical bonds remain intact in fullerene n~olecules.An investigation of the physical properties of such alkali-doped compounds may be called the fullerene physics of today; second approach concentrates on possible chemical reactions involving break- down of bonds inside the fullerene molecules and formation of derivatives. This province is the fullerene chemistry. Let us discuss these approaches at greater length and consider the principle results obtained.
3. Fullerite physics An important division of this science is structi~ralanalysis of fulleritc crystals.
It has necessitated the development of special structural methods related to so-called Rietveld refinement. This method, used in powder diff'ractometry, is basctl on the acception, from rational considerations, of apriori structural motlel ant1 its s~rl)secluc~~~t correction so that tlie positions of all the diffractiorl lines \yere coincident wit11 those derived from model calculations. 'l'o dcfinc reliably structures of various phases of pure and intercalated fullercnes this rncthotl is coml)inecl with a ~nctliodof integral intensity measurements of different X-ray diffraction lines, with Lauc methods to study single crystals, with neutron diffraction and electron diffraction mcthotls.
1) Pure fullerite C60
At room temperature a pure C60 has a crystalline I:CC structure (fig./I), but herewith the niolccules are orientationally disorclcretl tluc 10 tlieir rapitl quasi averaged spinning. In the X-ray time scalc all tlie four molecules of the cubic cell arc structurally equivalent. The lattice parameter a=14,16E compriscs tlie value of the van der Waals molecular diameter I) = 101:. At cooling belo\\! 'I' = 245) - 260 I< the 111 phase transition to a simple cubic lattice (SC) is observed. This transition was documented by different structural methods - powder, on single crystals (X-ray), and, also, neutron and electron diffractions. Differential scanning calorimeter method confirms that the phase transition is a first order. Temperature dependence of C60 molecules spinning characteristics was studied in detail using the NMR on 13c isotope. It was shown that above 140K there was one more phase transitio~l,leading to narrowing of NMR lines (fig.5). Effect of pressure. As the hydrostatic pressure is increased, the self-absorption edge moves to the red spectrum side and the absorption edge shape changes (fig.6). The compressibility modulus of CGO wasdefined from the displacement of the X-ray diffraction lines position under pressure. 2.Intercalated fullerenes
As it has been mentioned, an interest to these materials was essentially stimulated by observation of high-T superconductivity in C specimens annealed in C alkali-metal vapors (fig.7). Diffraction and nlorphology studies of C60 speci~ne~~s aged at elevated temperatures in alkali-metal vapors have shown that such treatmerlt gives rise to different phases in thc systenl AxCg. wherc A (Na,l<,Pl),Cs). The following isolated p1lasc.s have been clocnn~eotctl:
A2C60 - insulating ,
A3C60 -- concluctiiig ,
A4C60 - insulating ,
A6C60 - insulating , Structural fragments of these phases are shown in fig.8 where large L)alls stand for fullerene CGO molecule and small ones for alkali-metal atoms. Fig.9 depicts schematically phase diagrams for C(;O doped witli various alkali metals. All the diagrams are seen to be of the same type, they exhibit clcarly stoichiomctr~rphases, JOURNAL DE PHYSIQUE IV and the intermediate compositions correspond to two-phase mixtures. Of course this is a low-temperature part of the diagram of state. The questions of how these phases decompose or melt at elevated temperatures as well as the questions concerned with the value of their mutual solubility are to be quantitatively specified. It has to be noted, too, that ternary combinations of the type Ax A'3-xC60 (A and A' are different alkali metals) have already been synthesized. In order to specify the regions of existence of such phases one has to construct ternary diagrams of state. For some of them the phase structures have been already defined and it has been shown how A a~nd A' atoms get distri1)utc~tl in octahedral and tetrahedral interstitial positions. It is precisely for the double intercalant Rb2Cs C60 that a maximal T =31.31< is observed. c The calculation of the sizes of octahedral and tetraliedral interstitial sites and their comparison with alkali metals atomic radii-in order to construct rnodcls of their rational arrangement - are based on the structural models in which, usually, lhc van der Waals radius is taken to be
Rw = 5.01 E These calculations have already been performed both for real and hypothetic structures (BBC, BCT). Along with calculations of the exact position of diffraction lines (Rietveld refinement) this necessitated a great body of compuLatio11 and creation of special computer programs (EASY/PUIaVfZKIX, NRCVAX) and olliers.
The obtained results are rather promising, they suggest that the quantitative theory of formation of principal physical properties of intercalated fullerenes may be created earlier than it can be done for other multicomponent systems. Conductivity and superconductivity of alkali metals fullerides
) were studied most comprehensively for the systcni ICxCGO wlicrc, (Ax C 60 precisely, superconductivity had been discovered, and then the phase 1<:3C60 was identified as superconducting. Later in a series AxC60 other superconducting phases were found and, particularly, the triple ones of the type AxA'3-xC60 having Tc > 30K, which, presently, is exceeded only by compounds on the base of copper oxides. As it has been shown in fig. 7, Tc varies from 10I< for Na2CsC60 to 31I< for Rb2CsC60. It turned out that the Tc value depends explicitly on the lattice parameter of intercalated fullerites, i.e. on the atomic volume of cations penetrated into the fullerite lattice
(fig.10). The Tc value is seen to increase as the parameter a lis increased.
Importantly, that a change in (I can be attained both by variation of cations combination and by superposition of an external hydrostatic pressure. As this takes place, all the points fit well into the general regularity (fig.10). These results were the base for important experiments when along with alkali metals ammonium ions were used as intercalating ions, which readily led to additional increase of Tc (fig.11). The structure of the obtained phase and the arrangement of ions in interstitial sites were defined by X-raying (fig.12). Further understanding of the character of particular phases in tlje system AxCGO is corroborated by the calculations of the band electronic structure of these phases. The calculations were based on the Extended EI 5t Ikcl Theory (EAT). The results are shown in fig.13. The calculations show that Lhe 1-ermi levcl of the supercodci phase A3C60 locates near the maximum of the dcnsity of states of the conduction band, as it ought to be in accord with classic superconductivity theory. Investigations of variations of the Raman spectrum of C60, as an alkali metal was being intercalated, proved very useful. Fig.14 illustrates schenlatically individual Raman spectrum regions wiLh C9-58 JOURNAL DE PHYSIQUE IV
indications of what vibrational types are responsible for a particular spectrum region.
Observations of the K3Cs0 superconducting phase formation have shown that the high-frequency spectrum region changes during this event. Then as the
potassium content increases and the K6C60 phase forms the spectrum changes again (fig.15). These data suggest the conclusion that the occurrence of superconductivity in the KxCsO system is related to the electron-phonon interaction in vibrations of
the Ag(2). Signigicant role of the electron-phonon interactions in the process of current- carrier coupling in the K3CG0 system is also supportecl by tlic presence of isotopic
effect for T observable in K3Cg0 at substitution of ''K by 13~isotope (fig. 16).
These data bear witness for the fact that electron-phonon interactions play a significant role in the mechanism of the occurrence of high-tc~npcrati~re superconductivity of intercalated fullerencs. They also raise hope for consistent
construction of quantitative physical theory of this phenomenon [I ,3].
4. Fullerene chemistry Investigation of cliemical reactions which involve fullerenes ancl of the
properties of these reactions products is a vast ant1 rapiclly dcvcloping ficltl of today's
organic chemistry. Since this audience consists mainly of physicists, it would serve
no purpose to go into thc 11eart of the chemical prol)lcnis, I shalI, thercforc, only
briefly list them. The people interested in these questions I can refer to the excellent
review by Roger ?'aylor and Davicl R.Walton publisliecl in Naturc in thc~surlirnrr ol'
1993 [2]. Roughly speaking, all fullcrcnc compountls can l)c classcd into tllrcc categories:
1. Intercalated compounds wherein fullerene molecules in the crystal lattice sites retain their integrity and identity whereas foreign atoms occupy interstitial positions in the lattice. 2. Endohedral clusters obtainable upon capturing of a non-carbon atom inside a fullerene molecule (encapsulation). In this case the fullerene molecirle also retains its structure. 3. Exohedral solids formed from fullerenes to which foreign atoms or molecules are covalently bonded on the outside of the carbon cage.
We have already discussed the first type compounds. I can only add that intercalating atoms may be not orily alkali-metal atoms (cations), but, also, e.g. iodine atoms which, in these processes, probably manifest tlicri~selvcsas anions. The C60J4 phase was found in the C6+, syskm, its structure was examinecl by x-raying and characterized. Another interesting CGO derivative intercalated compound is tetrakis - dimethylaminoethylene (TDAI:) of the formula C2N4(CI 1:3)8. Despite a large number of different atoms is1 the rnolccule all of thcm havc a cornparativcly small atomic radius and molecules as a whole can locate in the interstitial sites of the CGOstructure. This compound, is specifically, a ferromagnetic, having the Curic temperature of about 16I<, which, so for is the highest anlong organic ferromagnetic. Seemingly, a partial charge transfer from intercalant's molecules (or atoms) to fullerene's molecules is of importance for structure stal~ilizationin all intercaiatecl compounds.
As for endohedral cluster solids, then wc know, so far, the La (a) CGO compound, where the symbol (a) implies that 1-a atoms arc insitlc thc cagc. 'l'hcrc were other attempts to synthesize endoheclral cluster solids wilh othcr rarc-citrtli atoms inside the cagc, liowcvcr, low quality of spccimcns iuid inacleq~~acyof experimental material do not make it possi1)lc to draw final conclusion about the crystalline structure of these conipounds. JOURNAL DE PHYSIQUE IV
An investigation of the chemical reactions leading to the formation of the
third type compounds i.e. exohedral ones as well as of the structure of these compounds is, precisely, the province of the fullerene chemistry comprising the main
ideas and approaches of organic chemistry. The key moment in the understandi~lgof
the fullerene molecule behavior in various chemical reactions is that the occurrence of the double bond in pentagonal ring must be excluded. There is only one way of
packing pentagons and hexagons so that a stable isomer could be formed. Some
versions are illustrated in fig.17. As contrasted from aromatic molecules, fullerenes do not possess atoms of hydrogen or other adtled groups, -- therefore, they are not
capable of substitution reiction. Substitution reactions can takc place only with derivatives, especially those formed by addition. 'l'he electronic structure of fullerenes molecules suggests that they ought to have an increased electron attracting. 'l'his governs their chemical behavior, for example, they readily react with nucleophiles. At a slow crystallization from benzene CsO fullerene molecules yield solvates,
(C6116)4C60 in which spinning of the molecules is so slow that it is possible, using x-ray diffraction method, to define the structure of the single crystals. The same results are obtained at crystallization from cyclohexanc. 'I'liere are some other complexes from which co-crystallization villi benzene occurs. All these materials obtained at co-crystallization exhibit so-called host-cluest structures, an example of which with ferrocene is shown in fig.18. l~lercis much in colnnion with intercalated compounds when structural stabilization occurs due weak interaction related to charge transfer.
Analogous structurs are obtained at the interaction with s~~lpli~ir(CG0S1 (j and C70S48). These are formed of S8 rings.
As for remaining typical chemical reactions of fullerenes, known by the present time, I shall restrict myself to their brief listing. Anion formation and oxidizing processes These processes are of clear electrochemical nature. In process is rather typical for organic chemistry and it is being intensively studied using platinum asacalalyst. The interaction of C60 with t-butyl-lithium belongs to the same class of reactions. Details of such reactions are rather complicated.
Addition reactions These reactions can be categorized into three groups:
1) Cycloadditions ,
2) Additions i~ivolvingbridging ,
3) Additions of separate groups , Category 2 comprises reactions with the formation of epoxides from isolated C60 These are oxygen bridges.
Addition of methylene to CGO and CTO goes via tlie forniation of' car1)on bridged. There are recent reports on synthesis of niethanofullerenes. In reactions will) metals than as aromatics. Among reactions of addition of individual groups one riiay distinguish addition of halogens and hydrogen. Only 24 groups can be atldecl to C 60 so that two of them were not neighbours (fig.19). Specific structure of CGOBr(; is shown in fig.20.
Polymerization
Polymers comprising C60 may be confincd to three types: CM'O of tli~~iiilre the pearl necklace type, fig.21, tlie third type is pendant chain, fig.21. Onc niay assume that their two- and three - dimensional versions may be describetl as a polymer net work or lattice. Probably, the third type having a direct 1)ond between tlie cagcs C9-62 JOURNAL DE PHYSIQUE IV
forms at polymerization of CGOunder the ultra-violet irradiation in the absence of oxygen. In conclusion of this section I give the general scheme of all chemical reaction involving fullerenes (fig.22). Conclusion It is clear that besides a great scientific interest investigations of fullerenes
promise considerable practical implementation. In addition to what has been already mentioned, they can be used in solid
state quantum electronics, optics and in production of electric batteries. Many opportunities for chcmical technology and chcrnical analyt~cal~llcthods are in sight.
REFERENCES
I. D. W.Murphy, F-T..J.Rosseinsky, I<. M.I'Icming, R.l'ycko, A.O. Ramirez,
R.C.Haddon, T.Siegrist, G.Dabhagh, .].C.Tully, R.E.Walstcclt ,
J.Phys.Chem.Solids., vo1.53, N11, 1321 (1 992). 2. R.Taylor, D.Walton,
NATURE, vo1.363, p.685 (1993) ,
3. O.Zhou, D.E.Cox, ,
Fig.1. Fullerene C60 molecule. Fig.2. Diamond crystal structure.
Fig.3. Graphite crystal structure. JOURNAL DE PHYSIQUE IV
Fig.5. 13c NMR spectra of solid CGOat indicated temperatures (a-g) h-tetramethylsilanc. Fig.6. Absorption edge spectra of C60 crystal at '1'= 300IC and pressure up to 20 GPa curves 1-6 correspo~idto pressure 0,0.9, 3.1, 9.5, 14,20. (>Pa respectively.
Fig.7. Shielding measure~nentfor AxAs _ 3C60 (~~onn;~lizcd). C9-66 JOURNAL DE PHYSIQUE IV
CbO (~cc) bct fcc
A+& bcc
Fig.8. Schematic structures of C60 and A C . C60 - large spllcrcs, A x 60. small spheres
> 7
Nax Nax 1phase 1phase ? ? phase 2phase 2 phase Ko+K3 K3+K4 lphase? Zphase 2phase - Rb3+&, @be 2 phase 2 phase Cso+ cs4 I I
Fig.9. Proposed phase cliagram for AxC60 K3CG0PRESSURE - A RbaCsoPRESSURE 0 A3Ce0 ONE ATM. o - Q 3 - cP
A= O - A
- A u
- =) A 0 -
0 I 1 1 qo a I 1 13.7 13.9 4 14.3 14.5 14.7 LATTICE PARAMETER, a ( A ) Fig.10. Relationship of thc si1perco1-1ductingTc to the unit cell size or A,,3 C 60'.
A3CG0 - normal pressure and - data from K3Cg0 and Rb3CG0 uncle prcssul-r
Temperature (K) Fig. 11. Normalized d.c. rnagnet~c susceptibilities of Na2CsC6. ancl
(NH3)4Na2CsCG0 measured i1-1 a field 2,s Oe. JOURNAL DE PHYSIQUE IV
Fig.12. A model of (NH:j)4Na2CsC60 with ordered Na(NH3)4 tetrahedra the
C, Na, Cs, N and H atoms are represented by grey, red green, t)cne and wllite spheres respectively
DMgnrofsTAIEbfrry Co
Fig.13. Energy band structure of the metall~c1<:3C60 c.o~n~)oullcl L-d-LL~"1.110 20 Sa iiL iii . . ..- 5001 I loo0 2000 FREOVENCY (cm ') Fig.14. Various vibrations in the A3C60 compounds can contribute to electron-phonon coupling and may be important for superconductivity.
6W z 3 B
1420 144Q 1480 FREQUENCY {a ') Fig.15. Raman spectra evidence for charge transfer from potassium atoms to
the C6-, molecules. JOURNAL DE PHYSIQUE IV
b I
z 0- omm**oeo*\ @pogmm.~..q,d*. 0 I F 0. 9 4 0. tS *' t z i. (3 l 2 - 0.09 - a l P W * 2 b tT2 p-0.18- l *
I I 1 I 18.0 18.5 19.0 19.5 20.0 TEMPERATURE (kelvin) Fig. 16. Isotopical effect. Magnetization transition in isotopically pure
K~~~c~~occurs at the temperature 0,4K lower than in K3 12CsO.
Fig.17. Possible disposition of two pentagonal rings adjacent to a hexagonal ring. Disposition b and c introdure instability. Fig. 18. Host-quest structure of CGO (ferr~cene)~
Fig.19. Schlegel diagram showing the 24 non adjacent sites in C60 JOURNAL DE PHYSIQUE IV
Fig.20. Structure of CGOBrl;
Fig.21.