摘要:

The magnetic phase transition of stage-2 CucCo1-cCl2GIC's has been studied using SQUID AC magnetic susceptibility. For 0.4 ≤ c ≤ 0.9 the system undergoes a phase transition at Tcland a reentrant spin glass transition at TRSG(<Tcl). For 0.9<c ≤ 0.93 the system undergoes a spin glass transition at TSG from the paramagnetic phase to the spin glass phase. No phase transition is observed for c = 1 at least above 0.3 K. The nature of reentrant spin glass phase and spin glass phase is examined from the frequency dependence of absorptionX″.

ISSN:1058-725X    

DOI:10.1080/10587250008025433

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Magnetic and transport properties of nanographites are investigated in graphite ribbons with zigzag and armchair edges. One of the most remarkable features of these systems is the appearance of edge states, strongly localized states near zigzag edges. Because the edge states lead to a sharp peak of density of states at the Fermi level, the graphite ribbons with zigzag edges show Curie-like temperature dependence of the Pauli paramagnetic susceptibility. This paramagnetic contribution competes with the orbital diamagnetism, leading to a crossover from high-temperature diamagnetic behavior to low-temperature paramagnetic behavior in nanographite ribbons with zigzag edges. The edge states are also responsible for the low-energy electronic transport properties. Here we study the junctions connecting nanographite ribbons of different width by the Landauer approach. The conductance as a function of the chemical potential shows rich structure and a large number of dips of zero conductance. The perfect reflectivity originates from the formation of standing wave resonances in the junction region.

ISSN:1058-725X    

DOI:10.1080/10587250008025434

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Graphite and fullerite C60exhibit low dimensionality crystal structures, which allow to observe numerous intercalation reactions. These latter are always accompanied with an electron transfer. When the graphene sheet or the fullerene molecule have been reduced, we obtain generally strongly reactive anionic species. However, their reducing character can disappear in several cases.

ISSN:1058-725X    

DOI:10.1080/10587250008025435

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Angular dependence of thec-axis magnetoresistance of stage-1 and stage-2 MCI2GIC (M=Cu and Co) was measured. Stage-1 CuCl2GIC shows an angular dependent magnetore-sistance oscillation (ADMRO) characteristic in the systems having a periodically-warped cylindrical Fermi surface (FS). This means that the conduction along thec-axis is band-like in spite of extremely large anisotropy in conductivity. On the other hand, the angular dependence of the magnetoresistance of stage-2 CuCl2GIC and stage-1 CoCl2GIC can be interpreted as the mixture of ADMRO based on a band conduction and incoherent interlayer hopping. Stage-2 CoCl2GIC shows only incoherent hopping. In low magnetic field region, thec-axis resistances of stage-1 and stage-2 CoCl2GIC are affected by the magnetic phase transitions. Spin-dependent tunneling effect can explain this phenomenon.

ISSN:1058-725X    

DOI:10.1080/10587250008025436

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The time dependent resistivity associated with the intercalation of alkali metal atoms and iodine molecules into “carbolite”, the quasi one dimensional carbon crystal, was measured at a constant temperature. After maintaining a value suitable for semiconducting behavior during a long time of intercalation, the resistivity suddenly decreased by several orders of magnitude, corresponding to a metallic conduction. Alkali atoms or halogen molecules randomly attacked the triangular lattice of the carbon chains and become located at the inter-chain sites. The intercalants of the nearest neighbor sites formed local clusters. As the intercalation proceeded, clusters aggregated to make larger clusters. When aggregation reached such an extent that the cluster sizes were comparable to the sample size, conducting paths throughout the sample opened up. This means that the resistance changes from semiconductive to metallic. This change occurs like an electronic phase transition as the nature of a percolation process.

ISSN:1058-725X    

DOI:10.1080/10587250008025437

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The kinetics of intercalation of halogen molecules Br2or ICI into pyrolytic graphite “NIKAFILM”, a commercial product of Nihon Carbon Inc., has been studied by the measurement of electron transport phenomena, especially the thermoelectric properties. The data were analyzed by a two-carriers band model, and it was concluded that the change in the resistivity and Seebeck coefficient is due to the increase in the positive hole density because the intercalant halogen molecules work as acceptors. From the weight increment the stage index was tentatively estimated to be four, and the deduced charge transfer rate was 1.33 × 10−4e/mole-cule.

ISSN:1058-725X    

DOI:10.1080/10587250008025438

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The graphite intercalation compounds CxC8F17SO3·yF and CxN(CF3SO2)2are prepared in 48% hydrofluoric acid, using the oxidant K2MnF6under ambient conditions. Analyses of PXRD peak position and periodic oscillation of the peakwidth indicate that the stable product CxC8F17SO3·4F is comprised of a random solid solution of stage 2 and 3. The addition of conc. HNO3or fuming H2SO4to 48% aqu. HF produces a stage 2 GIC. Structure refinement indicates a helical conformation of the anion. Stage 2 CxN(CF3SO2)2(x = 37) is obtained within 15 minutes under ambient condition in 48% aqu. HF. The anion orientations for these GICs are evaluated by structural refinement. Larger anions containing -CnF2n+1SO2substitutents can also be intercalated.

ISSN:1058-725X    

DOI:10.1080/10587250008025439

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Raman scattering and X-ray diffraction measurements were made to identify stage structure of CsC24(C2H4)nand CsC24(C2H3CN)n, which were exposed to air for a long time. Their electric conductivities were also measured during the long exposure to air. Raman spectra suggest that the gradual degradation of their electric conductivities in air is caused by the slow decomposition of the ternary GIC's from the periphery region, although results of X-ray diffraction for all samples indicate the retention of the initial stage structure. Among the samples, CsC24(C2H4)1.4which absorbed large amount of ethylene, was found to be exceptionally stable both in its stage structure and electric conductivity.

ISSN:1058-725X    

DOI:10.1080/10587250008025440

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Stage-1 nestled C14AsF6and un-nestled CxAsF6(x=10) were prepared by the reaction of graphite with O2AsF6or AsF5/F2, and novel adsorption behavior of nestled C14AsF16are discussed.

ISSN:1058-725X    

DOI:10.1080/10587250008025441

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The band structure and Fermi surface of C8K are studied by the first-principles calculation using two different types of basis sets to resolve the disagreements in the results of both experimental and theoretical studies. It is concluded that C8K is a compensated metal with the same number of holes and electrons. The Fermi surface of C8K is composed of the hole cylinders and electron prisms. The hole cylinders originated from the state in which the graphite interlayer state, π state, and potassium 4sstate are hybridized have the simply connected topology. On the other hand, the topology of the electron prisms originated from the π state is multiply connected with the electron tube. Furthermore, we calculate the cross sections of these Fermi surfaces and compare them with the dHvA frequencies. The observed two dHvA frequencies can be assigned to the maximum and minimum cross sections of the electron prisms. We also predict that four dHvA frequencies originated from the hole cylinders should be observed.

ISSN:1058-725X    

DOI:10.1080/10587250008025442

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor