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Nanoscopic AFM studies of electrobrightening of stainless steel show that, under well defined experimental conditions, a regular network of hexagonal cells (100 nm wide) can be observed at the surface of this alloy as it was at the electropolished aluminium surface. Its origin is tentatively attributed to an electroconvection process occurring at the metal/electrolyte interface.

A single crystal of the two-dimensional structure [NH3(CH2)4NH3]MnCl4 is studied by Electron Paramagnetic Resonance (EPR) when rotated around a ∗ , b and c axes, at X-band and room temperature. Magnetic susceptibility was also measured on a powder sample between 5 and 300 K. Intralayer exchange interaction J k = (4.6 ± 0.4) K calculated from anisotropy of the EPR linewidth is in good agreement with the value |J| k = (4.4 ± 0.1) K deduced from magnetic susceptibility measurements.

It is shown that the onset of the third harmonic susceptibility is the only appropriate criterium, when using AC susceptibility measurements, to determine the IL. Then, we show that the IL strongly depends on the crystallinity of superconductors and on the superconductor volume fraction in the composites. Besides, it is demonstrated, from transport measurements, that the IL corresponds to the J c = 0 line.

The thermal stability of fluorine-intercalated carbon fibres has been studied using differential thermal analysis and thermogravimetry. The selected host fibres were polyacrylonitrile-based and pitch-based carbon fibres, either as-received or heat-treated at 3000 °C. Fluorination performed at room temperature in the presence of hydrogen fluoride led to stage-1 compounds for the most graphitized samples. The thermal stability was found to depend on the host structure and on the amount of intercalated fluorine.

Intercalation of P-120 pitch-based fibers with bromine, from the vapor phase or liquid bromine, has been investigated. The maximum weight uptake was 20–25%, nearly independent of intercalation temperature. Intercalated samples were characterized by X-ray diffraction, Raman scattering and differential scanning calorimetry. Thermogravimetry experiments showed that a large amount (up to 50%) of bromine remains trapped in the fibers up to temperatures in the order of 1000 °C. Measurements of the transport properties (electrical conductivity, magnetoresistance and Hall coefficient) gave estimates of the concentration and mobilities of the charge carriers and of the charge transfer from carbon to bromine (0.5–0.6 electronic charge per Br2).

A high resolution transmission electron microscopy study of fluorine-intercalated carbon fibers has been carried out on two types of host materials: high-temperature treated pitch-based and PAN-based fibers. TEM images and corresponding Fourier transforms have shown that only stage-1 compounds and graphitic-type domains are detected in the experiment conditions. In particular, no interlayer spacing corresponding to higher staged materials have been noticed. The observed results can be correlated to the ratio of semi-ionic to covalent FC bonding previously determined by XPS. The disorder mostly depends on the nature of the host fiber and on the amount of mobile species that may react with the graphene layers during the deintercalation process, which is favored by the high-vacuum conditions.

We have studied the magnetism of annite mica (the Fe-end-member layer silicate having ideal structural formula: {K+}[Fe32+] 10 K and as large as Tc = 58 K in the true end member and a metamagnetic ground state spin structure (predominantly ferromagnetic layers with in-plane moments, stacked antiferromagnetically along the c∗-axis) that is stable despite significant amounts of Fe3+, diamagnetic octahedral ions, and Mn2+ in the natural sample. We propose that the antiferromagnetic stacking is part of the intrinsic zero-field magnetic domain structure and that it is entirely due to dipole-dipole forces. The most striking features are that a paramagnetic Fe2+ temperature dependent fraction persists far below Tc and that the Fe3+ moments abruptly disorder significantly below Tc, with the tetrahedral Fe3+ going first as temperature is increased. Plausible causes for the latter intrinsic features are discussed.

We report experimental data on the resistive transition of granular superconductive composites made of YBaCuO grains sintered in a CuO matrix as a function of temperature and grain concentration. The grain concentration dependence of the sample resistivity at constant temperature may exhibit two percolation transitions: a poor conductor-to-good conductor transition, which is present at every temperature, and a good conductor-to-superconductor transition below the grain superconducting transition temperature. We show that the temperature dependence of the superconductive critical concentration gives informations on the probability function describing the weak superconductive link transition to the normal state.

Characterization of powder samples of Zn 2− x M x P 2 O 7 (M = Mn, Cu; x = 0–2) shows that substitution of small amounts of Cu or Mn into low temperature or α-Zn 2 P 2 O 7 stabilizes a solid form isostructural with β-Zn 2 P 2 O 7 , the high temperature form. Single crystal X-ray analysis of ZnCuP 2 O 7 ; monoclinic space group C 2/ m , a = 6.741(5), b = 8.190(4), c = 4.542(3), β = 107.72(5)°, D calc = 4.210 g cm −3 , Z = 2, R = 6.6% for 353 observed reflections; shows mixed metal sites with 50% occupancy each of Zn and Cu. Octahedrally coordinated metal atoms lie on planes in hexagonal array with two oxygen atoms bridging adjacent metal sites. Magnetic susceptibility measurements of ZnMP 2 O 7 , M = Mn, Cu show antiferromagnetic interactions between cations which are stronger for M = Cu.

The solid solution, Cu 2−x Ni x P 2 O 7 (0≤x≤2), has been synthesized and characterized by X-ray diffraction on powder. A study of the crystal chemistry of this system has revealed the existence of a phase, Cu 2−x Ni x P 2 O 7 (0.04≤x≤1.75), isomorphous with the high temperature forms: β-Cu 2 P 2 O 7 and β-Ni 2 P 2 O 7 . The magnetism of this phase has been measured at x=0.25, 0.5, 1.0, 1.5 and 1.75 between 5.2 and 300 K. Antiferromagnetic interactions between ions weaken with the substitution of Ni 2+ for Cu 2+ in the solid state lattice of Cu 2 P 2 O 7 .

Samples of stage-2 fluorine graphite intercalation compounds (GIC) were studied by scanning tunneling microscope (STM) from submicrometer to atomic scale. From the STM view point, the most striking observation concerns the topographic modifications of the ( a , b ) sample surface induced by the intercalation process. Our STM images of a C 6 F compound are the first direct visualization of the fluorine atoms organization in the van der Waals gap.

We demonstrate that the skin effect and eddy currents in 123 / Ag composite have a strong influence on the real χ' and imaginary χ parts of the susceptibility measured by the AC technique. We think that the interpretation of susceptibility measurements (even made at low frequency) in terms of the critical-state model for determining critical currents on superconductor/good conductor composites is questionable because of the strong influence of metal addition on the imaginary part of the susceptibility.

Scanning tunneling microscopy (STM) has been used to image at atomic resolution the surface of pyrocarbons deposited at 1680-degrees-C and heat-treated at temperatures up to 2800-degrees-C. Information is obtained on the increase of surface order with HTT. Of special interest are the presence, in HTT 2000 samples, of point defects arranged in a (square-root 7 x square-root 7) R 19. 1-degrees superstructure and attributed to an array of interstitial carbon atoms, and the observation of a moire pattern in the HTT 2200 sample, which could be due to the turbostratic nature of the layer stacking.

Mixtures of ethylenedithio-dioctadecylthio-tetrathiafulvalene (EDT-TTF(SC 18 ) 2 ) with behenic acid form Langmuir-Blodgett films of Y-type characterized by islands of EDT-TTF(SC 18 ) 2 in a matrix of the fatty acid. A two-step oxidation (immersion in I 2 vapours followed by heating at 40°C) gives: • - an insulating brown phase with I 3 -isolated species. • - a conductive violet phase with I 3 -chains associated with a mixed valence state and a large structural reorganization.

Fluorine-intercalated graphite fibers have been synthesized at room temperature by direct reaction with elemental fluorine. The host materials were either vapor-grown fibers or pitch-based fibers. The CxF compounds obtained were mostly of the stage-3 type with a 12.65 A repeat distance. The carbon-to-fluorine atomic ratio ranged from 10 to 14. Resistivity measurements carried out between 4.2 and 300 K show clearly that the fluorination reduces the resistivity values, whatever the type of pristine material. For fluorine-intercalated pitch-based fibers an anomalous increase of resistivity below 30 K may be consistent with a weak electronic localization or with two-dimensional carrier-carrier interaction effects. In fluorine-intercalated vapor-grown fibers the anomalous bump observed around 190 K could result from a phase transition. The room temperature value of the conductivity of this type of material, i.e. σ = 1.6 × 105 S cm−1, is one of the highest ever observed for fluorine-intercalated CxF fibers.

We have obtained at 1173 K new diphosphates ( M , Cu) 2 P 2 O 7 with M = Mg, Ca, Sr, and Ba. The β-forms of Mg 2 P 2 O 7 and Cu 2 P 2 O 7 appear with a small quantity of Cu 2+ and Mg 2+ ions in their structure, respectively. The solid-solution β -Mg 2− x Cu x P 2 O 7 (0.04 ≤ x ≤ 1.94) at 298 K is continuous and isomorphous to β-Mg 2 P 2 O 7 and β-Cu 2 P 2 O 7 ; its limits were evaluated with DTA and X-ray techniques. Only three new phases CaCuP 2 O 7 , SrCuP 2 O 7 , and BaCuP 2 O 7 were isolated in the ( A , Cu) P 2 O 7 systems, A = Ca, Sr, and Ba. The two former are isomorphous to α-Ca 2 P 2 O 7 , while the X-ray spectrum of the latter is similar to that of BaCoP 2 O 7 and BaNiP 2 O 7 .

The X-ray absorption spectroscopy (EXAFS) technique has been used for studying the local environment of the metal in graphite intercalation compounds with transition metal dichlorides. For these compounds the octahedral environment of the cation is preserved after the intercalation process. A simulation of the first coordination shell with a two metal-ligand distance distribution enables the characterization of a strong distortion of the octahedra. The study of the radial distribution function around the metal atoms gives evidence of the existence of a second coordination shell.

The new charge transfer complex t-TTF-TCNQ, whose unsymmetric cation is intermediate between TTF and HMTTF, presents a regular stacking of both donor and acceptor chains. We show that this compound has a metallic behavior at high temperatures and undergoes one metal-insulator transition near 81 K. Its electrical and magnetic properties are examined in connection to this phase transition and the effective dimensionality.

Intercalation of RuF5 and OsF5 into graphite has been investigated using the vapor phase method. Stage 3 to stage 1 compounds were obtained depending on experimental conditions. The unit-cell constants of the intercalated layers were determined on Weissenberg patterns of a single crystal of C20RuF4.5 composition. A possible arrangement of (RuF4)n chains containing ruthenium in octahedral coordination is proposed. A charge transfer of 0.5 electron per intercalated RuF4.5 unit is deduced from the variation of CC bond length. Structural phase transitions have been investigated on single crystals between 120 K and room temperature. The material shows a metallic behavior and a hysteresis phenomenon occurring around 130 K in the resistivity variation may result from an incommensurate ⇌ commensurate transition. The magnetic behavior of Ru- and Os-intercalated salts is completely different from that of pure pentafluoride and corresponds to Ru(+IV) and Os(+V) species, respectively.

Static magnetic susceptibility anisotropy ( Δ X and EPR spectroscopy experiments have been carried out in the range 4 – 300 K on high-stage potassium intercalated graphite (HOPG). The magnetic anisotropy measurements show clearly the occurrence of first order phase transitions at about 230 K for KC 72 and 245 K for KC 144 and KC 168 . These transitions are attributable to order-disorder processes inside the potassium layers.

In this paper we report the preparation, crystal structure and some physical properties of the conducting molecular (Perylene) 2 [Pt(S 4 C 4 (CN) 4 )]. The crystal structure consists of segregated stacks of perylene and Pt S 4 C 4 (CN) 4 units, with a spacing of 3.3 A between the carbon atoms in the perylenes. The temperature dependence of the electrical conductivity is metallic with a maximum at approximately 15 K. At this temperature a sharp transition to an insulating state occurs. Magnetic suceptibility measurements confirm the existence of a transition in this temperature range.

The intercalation of nickel chloride into graphite in presence of chlorine gas has been studied in the temperature range 390 – 750 °C with an apparatus allowing the measurement of the chlorine pressure during intercalation. The results indicate that chlorine takes part in the reaction with a 600 mmHg threshold pressure below which no intercalation occurs. Between 495 and 690 °C, a second stage compound C 11.3 NiCl 2.13 , is obtained with the apparent activation energy of the intercalation being about 50 kcal/mole. X-ray investigations show that intercalated nickel chloride has a structure very close to the nickel chloride sandwich in free metal halide. However, intercalant layers are not complete, with the filling coefficient being at most 0.71. All of the data are consistent with an islandic nature of nickel chloride: islands of diameter 100 A allow explanation of the non integer stoichiometric coefficients given by chemical analyses and the amount of charge transferred from graphite to nickel, which is, moreover, consistent with a decrease of CC bond lengths as observed by X-ray diffraction.

The synthesis of graphite intercalation compounds with transition metal fluorides has been investigated. It is shown that, contrary to other 3d metal fluorides, TiF 4 can be easily intercalated as second-stage compounds, in presence of fluorine gas. From X-ray diffraction studies, evidence is given for the presence in the layers ionic TiF 6 -- and neural TiF 4 species. Finally, the intercalation of metal chlorides and fluorides is compared.

The study of the intercalation of 3d, 4d and 5d fluorides into graphite has been investigated. Novel graphite salts have been synthesized from various types of graphite with an excess of gaseous metal fluoride, either under vacuum or under fluorine atmosphere. Single-crystal structure studies at room temperature allow us to identify a second-stage compound with titanium tetrafluoride ( I C ≊ 11.35 A ) and graphite intercalation salts of different stages with ruthenium and osmium pentafluorides : the first-stage ruthenium compound has the identity period of 8.42 A. The magnetic behavior of the Ru-intercalated salt is completely different from that of pure RuF 5 : it suggested the presence of this element in the (IV) and (III) oxidation states. Conductivity measurements performed on a high-stage sample show a metallic behavior : the strong variation of resistivity observed at about 120 K could be due to an order-disorder transition within the a-b planes.

Magnetic susceptibility studies have been carried out on a series of polyacetylene samples doped with iron chloride either chemically or electrochemically at various doping levels. The data strongly indicate that the limiting stoichiometric coefficient for FeCl-4 is close to 0.05 and that chlorine is fixed at high doping levels. An intercalation model is proposed for the structure of these compounds, based on X-ray diffraction results and compatible with the composition found by magnetic studies.

The photooxidation of tetrathiatetracene TTT and its selenium analogue TSeT to halocarbon solutions by visible and UV irradiation have been studied. This reaction leads to the formation of new chlorine, bromine, and iodine radical-cation salts which have been characterized.

The spin density distributions in TCNQ anion-radicals are estimated from experimental fine structure parameters and crystallographic data of five TCNQ salts of 1—1 stoichiometry.

The intercalation of rhenium chloride into graphite from Re Cl5 in presence of chlorine gas has been studied. The maximum amount of intercaled chloride was obtained around 370°C and corresponded to the formula C9 Re Cl4 which was mostly of first stage with some admixture of higher stages. The crystal structure of the intercalated chloride is hexagonal with a-parameter of 6.50 A. The lattice is rotated by 20° from the carbon lattice: the two lattices are commensurate. Magnetic measurements seemed to show the presence of Re Cl4, although the existence of a mixture of Re Cl5 and Re Cl3 could not be excluded. Finally the electrochemical behaviour showed that the compound could be used as anode material in alkaline batteries.

The magnetic properties of M 2 Cu 2 O 5 (M = Y, Lu, Sc, In) have been investigated. The compounds have an antiferromagnetic ground state. The magnetic structure of Y 2 Cu 2 O 5 at 2K has been obtained using neutron diffraction. Cu 2+ ions are arranged in chains directed along the a-axis, which form isolated layers parallel to the (001) plane. The interplane coupling is antiferromagnetic, whereas two in-plane ferromagnetic couplings exist, one inside the chains (strong) and the other between the chains (weak).

The effect of temperature, moisture and current density on the stability of pitch-based fibers intercalated with metal chlorides is investigated. Particularly interesting are the high current densities available without degradation: current densities as high as 400 A/mm 2 can be maintained during several weeks without deintercalation. The results are explained using a free convection or radiation model. It is shown that the limiting value of current density is proportional to (ϱ d ) −1 2 under vacuum and to (ϱ d 2 ) −1 2 in gaseous atmosphere, where ϱ and d are the resistivity and fiber diameter, respectively.

Resume X-ray diffraction and high resolution electron microscopy studies have been carried out on single crystals of Madagascar natural graphite intercalated with several metal halides: NiCl 2 , MnCl 2 and CuCl 2 . The structure of the second stage CuCl 2 compound is reported. Then the results obtained for the three metal chlorides are compared.

We report the results of EPR studies on the ionic-radical salt (TEA) + (TCNQ) 2 - composed of an oganic free radical anion and a diamagnetic cation. Between about 40 and 80 K this crystal exhibits the triplet exciton EPR spectrum characteristic of an alternating chain of spins. The triplet spin Hamiltonian parameters are | D | = 44 ± 2 G and | E | = 5.5 ± 1 G. The directions of the zero field splitting principal axes are determined through single crystal rotation studies at 55 K and related to the crystal structure.

Intercalation of graphite with metal chlorides leads to compounds for which chemical analyses give non-integer stoichiometric coefficients. In particular, an excess of chlorine is observed with respect to free metal chlorides. For NiCl 2 intercalated graphite, the composition of the second-stage compound corresponds to the formula: C 11.3 NiCl 2.13 . This chlorine excess was accounted for by assuming the existence of small islands of intercalated chloride. As NiCl 2 -graphite compounds are known to undergo a magnetic phase transition at about 20K, neutron scattering and diffraction experiments were carried out in order to provide evidence for the islands and to specify the magnetic ordering at low temperature. From the small-angle scattering data collected below and above the magnetic transition, the first experimental evidence for the presence of intercalated islands has been obtained. The mean size of the islands is about 150 A, as previously assumed. From diffraction experiments, it has been shown that the spins of Ni 2+ ions in the magnetic phase are aligned ferromagnetically within the intercalant layer.

Because of the poor electrical conductivity of nickel hydroxide, NiCd alkaline batteries have a cathode consisting of a mixture of graphite and nickel hydroxide. The replacement of this two-phase mixture by a single phase consisting of the active material intercalated into graphite, should improve the battery efficiency. To this end, electrodes containing nickel chloride-graphite intercalation compounds underwent successive charge-discharge cycles at various rates. Their electrochemical behavior were comparable with those of classical graphite-nickel hydroxide mixtures. The electrode reactions have been followed by in situ magnetic measurements: during the early cycles, intercalated nickel chloride is converted progressively into nickel hydroxide by replacement of Cl− ions with OH− ions from the electrolyte.

The effects of intercalation with Br (residue) or CuCl 2 on the diameters d, microstructures, Young's moduli E, tensile strengths S and electrical conductivities of P-100 and P-120 fibers were determined using single filament methods. Circular cross section P-100, with an uncracked radial transverse texture, developed small axial cavities and longitudinal surface cracks on CuCl 2 intercalation, whereas the elliptical P-120 fibers with a “Pan Am” texture became more circular without evident damage on bromination. E decreases of 18% (P-120/Br) and 39% (P-100/CuCl 2 ) resulted from mean d increases of ≤ 11% and 28% respectively, which also contributed to a ∼ 38% decrease in mean S at 1 cm gage length in both cases. The gage length dependence of S increased for P-100 and decreased for P-120 due to changes in flaw distribution which depended on fiber and intercalant type.

The potentialities of graphite intercalation compounds as electrode materials in batteries are investigated. Emphasis is given to intercalated metal chlorides and their use in aqueous batteries. We show how classical systems can be improved and give examples of possible new electrode materials.

Single crystal structure studies at room temperature have been made for the first stage Mn Cl 2 intercalated graphite. The nominal composition was C 5·6 Mn Cl 2·4 , as deduced from chemical analyses and X-ray diffraction intensities. The data are in agreement with the island model, already proposed for Ni Cl 2 intercalation. From the decrease in C-C bond length and comparison with As F 5 compound, it is shown that the charge transfer is determined by chlorine in excess with respect to free metal halide.

The powder synthesis of Mg 3−x Cu x (PO 4 ) 2 (0 ⩽ x ⩽ 3) between 1173 and 1273 K, shows a discontinuous solid solution. The X-ray diagrams of compositions 0 ⩽ x ⩽ 1.70 are similar to that of Mg 3 (PO 4 ) 2 . The compounds with 2.30 ⩽ x ⩽ 3 are isotypic with the stanskiite-related structure of Cu 3 (PO 4 ) 2 . Magnetic measurements (4.2–300K) achieved on powder samples with x = 0.50, 1.00, 1.50, 1.70 and 3 are reported. An antiferrodistorsive ordering induced by the cooperative Jahn — Teller effect of Cu 2+ ions results in a one dimensional magnetic behaviour with the composition x = 3. The Bonner and Fisher's model for Heisenberg chains was used to determine the average value of the antiferromagnetic exchange.

The allotropic transformation of a TCNQ salt has been studied. For this the nucleation frequency of ensembles of small crystals was measured as a function of time, temperature, and crystal size by means of light microscopy. It was found that the measured proportion of transformed crystals can be described by a function of the type α=f(k T ·k s ·t ) with k T depending on temperature according to an Arrhenius equation, and k s being proportional to the edge length of the crystals. Furthermore the results cannot be described on the assumption of a single stationary nucleation frequency. The results are discussed with reference to other transformations, and it is concluded that there is a distribution of stationary nucleation frequencies.

Resume The kinetics of graphitisation of two carbons, a pitch coke and an acetylene black, were studied in the range 14002700°C. The evolution of the diamagnetic susceptibility and of the Hall coefficient, measured at room temperature, were followed as a function of treatment temperature and time. A phenomenological analysis of the results was used to determine the activation coefficient. In no case is the Arrhenius law (with a single, constant activation energy) obeyed. Results of a critical analysis of previous work are consistent with this conclusion.

The magnetic properties of graphite-MnCl2 intercalation compounds (stages 1 and 2) were investigated from 3 to 300K by EPR and static susceptibility experiments. The behaviour of the magnetic susceptibility anisotropy, EPR linewidth and g-factor gives evidence for short range order effects increasing sharply below 50K. The data are analyzed in connection with the two-dimensionality of the compounds.

The temperature dependences of g -factor and linewidth of C 11,3 NiCl 2,13 single crystals have been measured from 10 to 400 K. The data indicate that nickel ions in graphite behave at low temperatures like Ising ions, with a phase transition occurring at about 30 K.

The TCNQ anion radical salt of diethylcyclohexylammonium undergoes a first-order phase transition at ca.347°K, where sharp discontinuities of the heat capacity, electrical conductivity and paramagnetic susceptibility are observed.