Carbon is the most versatile element in the periodic table. Due to its ability to form both sp(3), sp(2), and sp hybrids and stable multiple p(pi)-p(pi) bonds, carbon can build up 3-, 2-, 1-, and 0-dimensionally structured substances with a broad variety of physical and chemical properties. In the last decade diamond films, active carbons, carbon fibres, and carbon-carbon composites were extensively studied. The discovery of C-60 opened up the world of spherical molecular carbon allotropes and gave rise to the development of diverse new materials comprising ultra-hard carbons as well as superconductors. In parallel, the discovery of the carbon nanotubes enabled the synthesis of new absorbents, catalysts and electron emitters. Several new carbon phases, like rectangular diamond or amorphous tetrahedral carbon, are discussed for special applications. (C) 1998 Elsevier Science Ltd. All rights reserved.

Early stages of the potassium-doping process of C60 were investigated with the EPR and MMMA techniques. Weak superconductivity of the (K + C60) mixture was found without heating or annealing the mixture. Upon heating two well-separated C601− and C603− EPR signals were found. Two superconducting phases with Tc(1) = (21 ± 0.5) K and Tc(2) = (18.5 ± 0.5) K were also distinctly separated by increase of the external magnetic field. To explain the appearance of the superconducting phase with Tc(1) which is 2.5 K larger compared to the standard Tc(2) of K3C60, a model has been developed.

C-60 fullerene was reacted with the three superacids HSO3F . SbF5 ("magic acid"), HSO3F and H2SO4 . SO3 ("oleum"). When added to HSO3F, C-60 is immediately solved physically to give a dark red coloured solution. After short time the colour changes to dark green indicating the formation of a charge transfer complex. Thereafter under exclusion of moisture and oxygen the solution proved to remain unchanged. In contrast, when exposed to the atmosphere the solution turned to be yellow coloured, due to the formation of the radical cation C-60(+), as could be shown by ESR measurements. C-60 itself is not soluble in magic acid. Therefore in this case we observed a slow but direct formation of the dark green charge transfer complex. Also here without adding an oxidizer no further reaction took place. With oleum C-60 gives first a dark green coloured solution and after some time - strongly depending on the concentration of SO3 - a yellow coloured solution, even without any contact to the atmosphere. Thus it can be concluded that SO3 is capable to oxidize C-60 to C-60(+) In 97 % H2SO4 we found evidence neither for the formation of a physical solution of C-60 nor for the formation of a charge transfer complex. However the anodization of a thin film of C-60 coated on a platinum electrode leads directly to the formation of the radical cation C-60(+).

Sulfuric acid, perchloric acid or nitric acid were attempted to intercalate into 2nd stage GICs with BiCl2, NbCl5 or InCl3 as well as into a 4th stage ZnCl2 GIC. In the case of 65% HNO3 it was found that intercalation can only be achieved with the 4th stage ZnCl2 GIC resulting in a biintercalation compound with two empty galleries per elementary cell remaining. In contrast, H2SO4 and HCIO4 formed saturated structures with all host lattices used as the starting material. Cyclovoltammetric measurements indicated that the insertion of H2SO4 or HCIO4 into the 4th stage ZnCl2 GIC proceeds stepwise. During the cathodic sweep the acids are completely deintercalated, as can be proved by X-ray diffraction measurements. If the insertion of H2SO4 into ZnCl2 graphite is terminated before all free galleries are occupied, HClO4 can be additionally inserted to form a triintercalation compound.

C-60/C-70 containing soot was produced by are-vaporization of graphite. The chromatographic separation of soot yielded fairly pure C-60 and C-70 samples. High-resolution FT-Raman spectra of C-60 and C-70 specimen as well as C-60 and C-70 solutions including polarization measurements are recorded. Compared to the spectrum of solid C-60, some Raman bands of the C-60 solution change their position and shape. Even the purest commercial C-60 samples contain solvent inclusions (impurities) in the order of some percentage. The chromatographic separation combined with Raman polarization measurements of solutions allows an evaluation of the fundamental vibrations of the C-60 molecule. Its assignment, in accordance with the group theoretical expectation, is proposed. The existence of small amounts of C-60 isomers (symmetry, e.g., C-2v, D-2h, D-2d) in icosahedral C-60 (I-h) is affirmed based on the polarization measurements. For C-70 the most extended set of Raman frequencies is presented.

C60 fullerene derivatives with H2SO4 (brown), HNO3 (light orange), and HClO4 (light brown) were prepared both by chemical and electrochemical oxidation of C60 in 97% H2SO4, fuming H2SO4, 65% HNO3, fuming HNO3, and 70% HClO4, respectively. A yellow-orange derivative was obtained by reacting the C60 fullerene with N2O5. In the case of the H2SO4 derivatives, the soccer ball structure of the C60 molecules proved to be maintained, whereas in the products obtained with HNO3, HClO4, and N2O5, the structure is different.

Low-temperature nuclear orientation of 203Hg by electric quadrupole interaction has been observed in graphite intercalation compounds of HgCl2. The measured electric field gradient Vzz = −0.75(8) × 1022 V m−2 is compared with the results on ion-implanted 203Hg samples and also with reported values in other intercalation compounds. Advantages and disadvantages of using intercalated samples, instead of ion-implanted samples, in nuclear orientation experiments are discussed.

Re2O7 was inserted into the graphite lattice to give fifth-, fourth-, and third-stage graphite intercalation compounds (GICs), depending on the reaction temperature. With ReO3NO3 a second-stage GIC could be obtained. In both compounds the intercalate layer structures proved to be different from the structures of free Re2O7 and ReO3NO3.

The intercalation reaction of HNO3 into graphite was investigated by means of electrochemical methods, x-ray diffraction measurements, and gravimetric studies. A first stage nitric acid GIC could be prepared by anodizing HOPG in fuming nitric acid. The intercalation process was found to cover both diffusion and another mechanism, which might be identified with sliding. The reversibility of the intercalation reaction depends on the degree of overoxidation; only samples having been oxidized beyond C+42 can be reduced to pure graphite.

The electrochemical properties of the interface between graphite sample and electrolyte solution will change during the anodic intercalation process. The physical quantities which indicate these electrochemical properties can be calculated from the results of the AC impedance measurements. An equivalent circuit is suggested for the calculation. The results of this method are in very good agreement with those from other methods, therefore it is very helpful for studying the kinetics of the anodic intercalation process into graphite in the electrolyte solution.

Nitrate melts with Ce, Hg, Pt and Au were prepared by adding nitric acid to the nitrates. Subsequently graphite was immersed in the melts. Depending on the reaction conditions first, second, third, fourth and sixth stage graphite intercalation compounds (GICs) were formed.

New graphite bi-intercalation compounds with BiCl3/H2SO4, InCl3/H2SO4 and BiCl3/AuBrx have been prepared. It could be proved that the insertion of bisulfate starts at each free interlayer gap at the same time. Furthermore two tri-intercalation compounds with BiCl3/AuBrx/H2SO4 and BiCl3/AuBrx/TlCl3, respectively, and a quadri-intercalation compound with BiCl3/AuBrx/TlCl3/H2SO4 could be obtained.