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Sodium−hydrogen−C60 ternary compounds have been prepared by intercalation of sodium hydride (NaH) into C60. This method afforded a high-quality superconducting (SC) sample with a large volume fraction, but on the other hand, only a few high-quality SC samples were obtained and most of the samples were nonsuperconducting. However, we have succeeded in transforming a non-SC sample into an SC sample and in enhancing superconductivity. The Rietveld analysis clarifies that the non-SC phase (α-phase) has an orthorhombic structure, in contrast to a cubic structure for the SC phase (β-phase). The absence of superconductivity in the α-phase will be understood by the broken symmetry.

We have found a new superconducting (SC) phase with the nominal composition (NaH) 4 C 60 , which was prepared by direct intercalation of sodium hydride (NaH) in C 60 . In a SQUID magnetization measurement, the SC transition temperature was found to be 15 K and the SC volume fraction was estimated to be 65%. The large value of the volume fraction suggests the creation of a single phase. This was confirmed by the powder X-ray profile showing a single f.c.c. phase with a lattice constant a=14.356(3) A . Hydrogen in the SC sample was analyzed by thermal desorption spectroscopy.

We have prepared sodium-doped C60 utilizing the thermal decomposition of sodium azide (NaN3). The strong low-magnetic field microwave absorption with a clear hysteresis was observed in the samples of NanC60 (n=3∼4), indicating the superconducting nature. By means of a SQUID measurement, the superconducting transition temperature is found to be around 12 K. Significantly, elemental analysis detected a nitrogen which was surely produced in the process of the thermal decomposition of NaN3. We suppose that this new superconducting phase will be NaxNyC60 where x is between 3 and 4, and y is unknown. This is the first superconducting material in Na-doped C60 without other alkali metals.

A conducting crystal of (phthalocyaninato)cobalt hexafluoroarsenate CoPc(AsF6)0.5 is prepared by an electrochemical method. Temperature-dependent electrical conductivity of dc and 9.4 GHz shows that CoPc(AsF6)0.5 is a narrow-gap semiconductor with activation energies of 327 K for dc and 138 K for 9.4 GHz. Thermoelectric power is +40 μV/K - +50μV/K in the range 100–300 K. The sign of the thermoelectric power is consistent with our earlier spectroscopic result that Pc ring is mainly oxidized contrary to the analogous material CoPcI. Optical spectrum along the c axis exhibits strong and weak peaks at 0.29 eV and 1.2 eV. Magnetic susceptibility is composed of a Curie-Weiss part with C = 0.056 emu mol−1 and a nearly temperature-independent part with the magnitude of 5 × D−4 emu/mol/ All these data indicates the localizaion of holes (U>4t) like in (TMTTF)2X and Ag(DMe-DCNQI)2. This localization seems to be related to the exchange interaction between the unpaired d-electron on Co and the π-electron on macrocyclic ligand.

We present a Raman scattering study of pristine and K doped C 60 at various doping levels by exciting in the near-IR at 1.16 eV. The normal metallic state of K 3 C 60 is characterized by a broad scattering background and by the resonance of low energy phonons in the range of 250–500 cm −1 . We assign the broad background to an electronic Raman scattering due to low energy electronic excitations. This spectral feature is indicative of an anomalous normal state behaviour and is similar to the case of high temperature ceramic superconductors. In the overdoped K 6 C 60 the squashing mode at 278 cm −1 shows a Fano resonance with the electronic scattering associated with localized electronic excitations which are characteristic of isolated regions of K 3 C 60 into the matrix of K 6 C 60 as a result of inhomogeneous doping. The Fano resonance indicates a specific electron-phonon coupling of this Jahn-Teller mode with low energy excitations and suggests that the symmetry of this electronic excitation is h g (i.e. the same of the coupled phonon mode). We discuss the nature of the anomalous electronic Raman scattering in terms of scattering from low energy excitations involving a low lying singlet band resulting from electron correlation and/or dynamical J-T distortion caused by the squashing mode.

We reported design and synthesis of new peri-condensed heterocycles which do not contain TTF type conjugated systems, that is, three isomers of dithiaperylenes (DTPR), one isomer of dithiapyrene (DTPY) and their methylthio or methylseleno derivatives. These donors showed two-stage redox behavior whose potentials are comparable to that of TTF. Good correlation was obtained between the oxidation potentials and the HOMO energies calculated by the PM3 method. A number of CT complexes prepared were classified into three groups, neutral, ionic, and non-V-shape groups. Among them, the non-V-shape group complexes contained highly conducting complexes including molecular metals. Most of the CT salts with inorganic anions having high conductivities showed lower electronic transition energies than 0.5 eV.

A novel butterfly-shaped bis(1,3-dithiole) donors containing a fused naphthalene and a 1,2,5-thiadiazole ring afforded cation radical salts showing metallic temperature dependence of conductivity.

Novel TTF vinylogues with extended π-conjugation have been synthesized using an oxidative dimerization reaction of 1, 4-dithiafulvenes. The cation radicals of the derivatives with o-substituted phenyl groups are thermodynamically stable where the aryl units are twisted and the TTF vinylogue skeleton is planar. Some compounds afforded cation radical salts upon electrochemical oxidation. X-ray structure analyses revealed unusual crystal structures.

The magnetic properties of the superconducting sodium-hydrogen-C 60 ternary compound have been investigated by means of SQUID and ESR. The superconducting parameters (the penetration depth λ and the coherence length ξ) are estimated to be λ=2800 A and ξ=38 A using H c1 (0)= 90 G and H c2 (0)= 22 T. The spin susceptibility and the ESR linewidth decrease sharply below ~250 K, suggesting the presence of some phase transition.

Novel nonplanar bis(1,3-dithiole) donors with small on-site Coulomb repulsion afforded unusual cation radical salts as single crystals whose properties were strikingly affected by the incorporated solvent molecules.

The Na-doped C60 superconductor prepared from sodium azide (NaN3) were systematically studied. Superconducting (SC) transition temperature (Tc) was evaluated to be 12–17 K from the low-field signal (LFS) of microwave absorption (MA) measurement. Several parameters such as critical field of the Josephson junction, the bulk Hc1(0) and Hc2(0), the London penetration depth and coherence length were estimated from LFS and SQUID experiments. The Pauli contribution increases with increasing SC volume fraction, but Curie spins are still detected at the low temperature even in the best sample with 38% of SC volume fraction.

We have prepared Na4C60 samples by the different ways of the thermal decomposition of sodium azide NaN3. The superconducting (SC) samples were obtained by the decomposition under the dynamic vacuum, while the non-SC samples by the decomposition in the sealed tube. The SC sample was composed of two fee phases with a lattice constant a=14.207(5)A (phase A) and a=14.339(4)A (phase B). On the contrary, the non-SC sample had single fee phase which can be assigned to phase A. This result strongly suggests that phase B is the SC phase.

Fluorine-graphite intercalation compounds C x F (15>×≥5.6) have been obtained by exposing HOPG to fluorine with available highest purity, at 50°C for periods exceeding 30 days. The identity period and the intercalant thickness of pure stage-2 compound C 6.4 F are, respectively, 9.46 and 2.76 A. In-plane electrical conductivities of C x F are ca. 8–10 times that of the pristine HOPG. The c-axis resistivity of the stage-2 compound vs. temperature shows a maximum at 194 K; metallic-like behavior at lower temperatures and semiconductor-like behavior at higher ones. The compound also shows an anomalous c-axis thermal expansion at 130 K and a drastic motional narrowing in the linewidth of 19 F-NMR at 150 K, suggesting a kind of in-plane phase transition of intercalated fluorine.

New organic conductors, (BEDT-TTF) 5 Hg 3 Br 11 and (BEDT-TTF)HgBr 3 (BEDT-TTF: bis(ethylenedithio)tetrathiafulvalene) are prepared, and their crystal structures, transport properties, and ESR are investigated. In the former complex, 3 10 of the BEDT-TTF molecules are incorporated in the anion sheet as BEDT-TTF 2+ . This complex shows, in spite of its complicated 7-fold periodicity, metallic conductivity down to 120 K.

The magnetic property of an organic conductor, (TTM-TTF)(I 3 ) 0.823 , has been investigated by means of ESR measurement. An ESR spectrum consists of two signals; a sharp signal due to conduction electron spins on TTM-TTF molecules and a broad signal due to localized spins on iodine molecules. The spin susceptibility associated with the sharp signal shows a metal-insulator transition around 100 K. The strong temperature dependence of the g-value for the broad signal suggests the change in the electronic state of the iodine acceptor accompaning the phase transition.

Superconductivity of the compounds of LaMCuO system with K2NiF4 type structure has been studied. For the sintered compounds with MBa, Sr and Ca, the highest onset transition temperatures, Tci, estimated from resistivity measurement are about 36.9K, 43.0K and 23.5K, respectively and the highest temperatures where the resistivity vanishes, Tcf, are about 27.8K, 34.0K and 15.5K, respectively. Almost complete Meissner effect has been confirmed by low frequency ac susceptibility measurement. Crystals of the compounds with MBa and Sr have been prepared. As the result of the preliminary experiment for a crystal with Ba, it is found that Tcf of the crystal is higher than any one of the sintered specimens with MBa, while the Tci of the crystal is nearly the same as the highest one of the sintered specimens.

Using nonresonant microwave absorption in low magnetic field (so called LFS) combined with conventional ESR it is shown that degradation of the superconducting (SC) state of K X C 60 upon exposure to air is a surprisingly slow (e.g. compared to n-type doped conducting polymers) and partially reversible process. The annealing at 100–130°C in high vacuum of air exposed samples restores both LFS and ESR typical for the SC state, suggesting the formation of some unstable (K X C 60 O 2 ) complex at a first stages of oxidation. At longer exposure times superconducting LFS can not be recovered meaning irreversible chemical bonding of 0 to C 60 .

Charge transfer complexes of polycyclic aromatic hydrocarbons with alkali metal are known to adsorb hydrogen chemisorptively. We investigate hydrogen uptake effects on the properties of metallic K 3 C 60 by means of ESR and superconductivity measurements. The introduction of hydrogen induces a disproportionation reaction, resulting in the generation of K 6 C 60 domains which have interstitial sites available for the accomodation of dissociated hydrogen atoms. The annealing process makes the hydrogenated K 3 C 60 homogeneous where small amounts of hydrogen are stabilized as impurities. Superconductivity is not influenced by hydrogen uptake.

By means of low magnetic-field micowave absorption (Low-Field Signal) and conventional ESR, we have studied the evolution of superconductivity in bulk KxC60 dependent on the variation of K- doping temperature and time. The first LFS as an occurrence of superconductivity is observed in a doping time as short as td = 0.5 h with a discrete Tc ∼ 19 K, and the volume of the superconducting phase increases on further dopings, while Tc changes slightly. The sample in a superconducting state exhibits strong ESR absorptions, which indicates the presence of a non-superconducting metallic phase coexisting with a superconducting phase in inhomogeneously doped KxC60. These phases are closely correlated and disappear at the same time by overdoping.