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International audience; In order to account for the large drop of superconducting critical temperature, T, and for the dramatic increase in residual resistivity, rho(0), previously reported in CaC6 at P-cr approximate to 9 GPa, we studied the room-temperature crystal structure of bulk CaC6 samples as a function of pressure up to 13 GPa by means of synchrotron x-ray diffraction in diamond anvil cells. At P-cr, we found no change of the trigonal R m space group symmetry, but a large increase in isothermal compressibility, kappa, from -0.0082 GPa(-1) to -0.0215 GPa(-1), accompanied by a large broadening of Bragg peaks. With both effects being reversible, it follows that superconductivity in CaC6 is maximized at the verge of a peculiar order-disorder phase transition concomitant to a large lattice softening. Space group symmetry considerations supported by ab initio calculations of the relaxed structure within the density functional theory lead us to conclude that the disordered phase is presumably characterized by a random off-centering of the Ca atoms in the ab plane with respect to the C honeycomb layers.

We report the comparative structural-vibrational study of nanostructures of nanourchins, nanotubes, and nanorods of vanadium oxide. The tube walls comprise layers of vanadium oxide with the organic surfactant intercalated between atomic layers. Both Raman scattering and infrared spectroscopies showed that the structure of nanourchins, nanotubes, and nanorods of vanadium oxide nanocomposite are strongly dependent on the valency of the vanadium, its associated interactions with the organic surfactant template, and on the packing mechanism and arrangement of the surfactant between vanadate layers. Accurate assignment of the vibrational modes to the V-O coordinations has allowed their comparative classification and relation to atomic layer structure. Although all structures are formed from the same precursor, differences in vanadate conformations due to the hydrothermal treatment and surfactant type result in variable degrees of crystalline order in the final nanostructure. The nanotube-containing nanourchins contain vanadate layers in the nanotubes that are in a distorted γ- V5+ conformation, whereas the the nanorods, by comparison, show evidence for V5+ and V4+ species-containing ordered VOx lamina.

Lithium intercalation in phase-pure nanocrystalline brookite TiO2 is demonstrated for the first time. Galvanostatic studies show that 0.9 Li per formula unit can be intercalated into this phase in initial discharge. Ex situ X-ray diffraction studies on the electrodes at different levels of lithium intercalation show that the structure is stable toward lithium intercalation and deintercation. In the initial charge, an irreversible capacity loss is observed. However, on further cycling, the phase shows excellent cycling behavior. A reversible capacity of 170 mAhg-1 is observed even after 40 cycles. � 2006 The Electrochemical Society.

In this study, we focus on the synthesis of ternary nitrides with the general formulation Li3-nxMx[]nx-xN (Mn+ = Co2+, Cu+ and Ni2+, [] represents vacancies) by a solid state route, under a controlled atmosphere, for a large composition range (0 < x = 0.6). The lattice parameters evolution obtained for these nitrides and a detailed analysis of X-ray diffraction data show the presence of Co2+ and Ni2+ in the interlayer spacing and the simultaneous presence of vacancies in the nitride layer. In the case of copper materials, Cu+ ions are present in the interlayer site, without any vacancies in the nitride layer. Once we master all parameters of the synthesis, we study the structural characterization and the electrochemical properties of each compound in terms of specific capacity, rechargeability, cycle life and kinetics. In all cases, we demonstrate that the redox systems involve several metal oxidation states, but also oxidation of nitrogen through (metal-N) entities. Galvanostatic performances are largely dependent on the metal and the potential range. Intercalation compounds are concerned in the potential range [0.02 – 1.0] V vs. Li+/Li because they involve the electrochemical systems CoII/CoI and NiII/NiI, with reversible Li insertion in vacancies and stable but low capacities (180 mAh.g-1). An optimisation of the electrochemical performances is possible when the potential range is extended up to 1.1 V. Thus, a stable specific capacity of about 320 mAh.g-1 is recovered after hundred of cycles, for the material Li2.23Co0.39N., Dans ce travail on réalise la synthèse de nitrures doubles de lithium et de métal de type Li3-nxMx[]nx-xN (Mn+ = Co2+, Cu+ et Ni2+, [] représente les lacunes en ions Li+) par une méthode céramique, sous atmosphère contrôlée, pour une large gamme de composition (0 < x = 0,6). L'évolution des paramètres de maille de ces nitrures et l'analyse fine des diagrammes de diffraction des rayons X indiquent la présence de Co2+ et de Ni2+ en position interfeuillets, ainsi que la présence simultanée de lacunes dans le plan azoté. Dans le cas du cuivre, des ions Cu+ interfeuillets sont présents, sans lacunes dans le plan azoté. Après avoir acquis la maîtrise des paramètres de synthèse, nous réalisons la caractérisation structurale et l'étude des propriétés électrochimiques de chaque matériau en terme de capacité spécifique, rechargeabilité, durée de vie, cinétique, etc. On démontre dans tous les cas que les systèmes redox impliqués font intervenir les divers degrés d'oxydation des métaux mais également ceux de l'azote à travers d'entités (métal-N).Les performances en cyclage galvanostatique sont largement dépendantes du métal et du domaine de potentiel concerné. Des matériaux d'intercalation du lithium sont concernés dans le domaine de potentiel [0,02 – 1,0] V vs Li+/Li car ils ne font intervenir que les systèmes CoII/CoI et NiII/NiI, avec insertion du lithium dans les lacunes, et des capacités stables mais restreintes (180 mAh.g-1). Une optimisation des performances est possible si on étend le domaine de cyclage à 1,1 V, avec une capacité spécifique stable de l'ordre de 320 mAh.g-1 sur plusieurs centaines de cycles, pour le matériau Li2,23Co0,39N.

We present a semimathematical model for the simulation of the impedance spectra of a rechargeable lithium batteries consisting of porous electrodes with spherical Li+ intercalation particles. The particles are considered to have two distinct homogeneous phases as a result of the intercalation and deintercalation of Li+ during charge and discharge. The diffusion of Li+ ions in the two phases and the charge transfer at the solid electrolyte interface (SEI) are described with a mathematical model. The SEI and the electrolyte are modeled using passive electronic elements. First, this model is derived for a single intercalation particle consisting of two different solid phases. This model is then transformed to a continuous model and applied to a single porous electrode, where the sizes of the particles are assumed to have on average two grain sizes where the radii are Gaussian distributions. Finally, this model is further developed to simulate the impedance of a rechargeable lithium-ion battery.

We present electrical resistivity (ρ) measurements for the intercalation compound Fex TiSe2 (0≤x

The structural, energetic, and electronic properties of the Li/graphite system are studied through density functional theory (DFT) calculations using both the local spin density approximation (LSDA), and the gradient-corrected Perdew-Burke-Ernzerhof (PBE) approximation to the exchange-correlation energy. The calculations were performed using plane waves basis, and the electron-core interactions are described using pseudopotentials. We consider a disperse phase of the adsorbate comprising one Li atom for each 16 graphite surface cells, in a slab geometry. The close contact between the Li nucleus and the graphene plane results in a relatively large binding energy (larger than 1.1 eV). A detailed analysis of the electronic charge distribution, density difference distribution, and band structures indicates that one valence electron is entirely transferred from the atom to the surface, which gives rise to a strong interaction between the resulting lithium ion and the cloud of pi electrons in the substrate. We show that it is possible to explain the differences in the binding of Li, Na, and K adatoms on graphite considering the properties of the corresponding cation/aromatic complexes.

LiCoAsO4 is synthesized by solid state reaction method and its crystal structure has been refined by the Rietveld method using powder X-ray diffraction data. LiCoAsO4 crystallizes in olivine structure with space group Pnma and orthorhombic lattice parameters are a = 10.4614(2) �, b = 5.9970(1) � and c = 4.8866(1) �. Electrochemical studies reveal that in LiCoAsO4, lithium is deintercalated and intercalated at high voltage ?5.0 V. On the other hand, the compound can react with about 9Li on discharge to 0.05 V. A reversible capacity of ?100 mAh/g is obtained in the voltage range 1.0-2.5 V. � 2005 Elsevier Ltd. All rights reserved.

Publisher's Version We present transmission measurements through tungsten tri-oxide nanostructures and thin films prepared by sol-gel process on micro-contact printed substrates. Identical electrochromic switching times are found for both the nanostructures and the bulk films with equal thicknesses upon intercalation of H+ ions. We attribute the large change in the transmission through nanostructures at 632 nm, which can not be solely explained by absorption, to diffraction effects. Q2 WOS:000235139500001

In this study, we focus on the synthesis of ternary nitrides with the general formulation Li3-nxMx[]nx-xN (Mn+ = Co2+, Cu+ and Ni2+, [] represents vacancies) by a solid state route, under a controlled atmosphere, for a large composition range (0 < x = 0.6). The lattice parameters evolution obtained for these nitrides and a detailed analysis of X-ray diffraction data show the presence of Co2+ and Ni2+ in the interlayer spacing and the simultaneous presence of vacancies in the nitride layer. In the case of copper materials, Cu+ ions are present in the interlayer site, without any vacancies in the nitride layer. Once we master all parameters of the synthesis, we study the structural characterization and the electrochemical properties of each compound in terms of specific capacity, rechargeability, cycle life and kinetics. In all cases, we demonstrate that the redox systems involve several metal oxidation states, but also oxidation of nitrogen through (metal-N) entities. Galvanostatic performances are largely dependent on the metal and the potential range. Intercalation compounds are concerned in the potential range [0.02 – 1.0] V vs. Li+/Li because they involve the electrochemical systems CoII/CoI and NiII/NiI, with reversible Li insertion in vacancies and stable but low capacities (180 mAh.g-1). An optimisation of the electrochemical performances is possible when the potential range is extended up to 1.1 V. Thus, a stable specific capacity of about 320 mAh.g-1 is recovered after hundred of cycles, for the material Li2.23Co0.39N., Dans ce travail on réalise la synthèse de nitrures doubles de lithium et de métal de type Li3-nxMx[]nx-xN (Mn+ = Co2+, Cu+ et Ni2+, [] représente les lacunes en ions Li+) par une méthode céramique, sous atmosphère contrôlée, pour une large gamme de composition (0 < x = 0,6). L'évolution des paramètres de maille de ces nitrures et l'analyse fine des diagrammes de diffraction des rayons X indiquent la présence de Co2+ et de Ni2+ en position interfeuillets, ainsi que la présence simultanée de lacunes dans le plan azoté. Dans le cas du cuivre, des ions Cu+ interfeuillets sont présents, sans lacunes dans le plan azoté. Après avoir acquis la maîtrise des paramètres de synthèse, nous réalisons la caractérisation structurale et l'étude des propriétés électrochimiques de chaque matériau en terme de capacité spécifique, rechargeabilité, durée de vie, cinétique, etc. On démontre dans tous les cas que les systèmes redox impliqués font intervenir les divers degrés d'oxydation des métaux mais également ceux de l'azote à travers d'entités (métal-N).Les performances en cyclage galvanostatique sont largement dépendantes du métal et du domaine de potentiel concerné. Des matériaux d'intercalation du lithium sont concernés dans le domaine de potentiel [0,02 – 1,0] V vs Li+/Li car ils ne font intervenir que les systèmes CoII/CoI et NiII/NiI, avec insertion du lithium dans les lacunes, et des capacités stables mais restreintes (180 mAh.g-1). Une optimisation des performances est possible si on étend le domaine de cyclage à 1,1 V, avec une capacité spécifique stable de l'ordre de 320 mAh.g-1 sur plusieurs centaines de cycles, pour le matériau Li2,23Co0,39N.

Four new low-dimensional phenylarsonates, A(HO 3AsC 6H 5)(H 2O 3AsC 6H 5) (A = Tl(1), Na(2), K(3) and Rb(4)), have been synthesized and characterized by X-ray diffraction, spectroscopic and thermal studies. They crystallize in triclinic unit cells and have approximately planar arrangement of A+ ions, coordinated to oxygen atoms of phenylarsonates, on both sides. Structure of thallium phenylarsonate as determined by single crystal X-ray diffraction, is one-dimensional, whereas those of alkalimetal analogues are two-dimensional. Successful intercalation reactions of compounds 1 and 2 with primary n-alkyl amines have been demonstrated. � Indian Academy of Sciences.

Microwave quality factor measurements for pure and mixed stages of graphite ferric chloride intercalation compounds have been carried out at X-band microwave frequency of 9.1582 GHz. The change in quality factor and hence the loss confirms the metallic nature of the graphite ferric chloride intercalation compounds that were studied. ? 1997 Elsevier Science S.A.

This work is devoted to the study of the functionalization of the carbon nanotubes (CNT)and to the application of the derivatives thus obtained to the development of nanomaterials, anessential topic in advanced materials science.A study of the functionalization by oxygen and fluorine of various types of CNT, obtainedby different methods of synthesis, was carried out, which enabled us to obtain tubesbifunctionalized by heteroelements.The storage of fluorine into single-wall CNT bundles could be realized under a F2 gasatmosphere, at low temperature. The fluorination thus obtained happens to be reversible.WF6 was intercalated in the interlayer space of catalytically-grown multi-wall CNTs. Theproduct obtained was used as template to obtain nanoparticles of tungsten oxyfluoride,following a fluorine-oxygen exchange via the hexamethyldisiloxane molecule.Finally, the development of nanowire-shaped halides using a fluorinated CNT asprecursor was attempted.; Ce travail est consacré à l'étude de la fonctionnalisation des nanotubes de carbone (NTC)et à l'application des dérivés obtenues en vue de l'élaboration de nanomatériaux qui font àl'heure actuelle l'objet d'une attention scientifique très soutenue.Une étude de la fonctionnalisation par l'oxygène et le fluor de différents lots de NTC,obtenus par différentes méthodes de synthèse, a été réalisée. Celle-ci nous a permis dedéboucher sur l'obtention de tubes bifonctionnalisés par des hétéroéléments.Le stockage de fluor dans des NTC monoparois en forme de fagot a pu être réalisé à partird'une atmosphère gazeuse de fluor à basse température. La fluoration obtenue s'est montréeréversible.WF6 a été intercalé dans l'espace interplanaire de NTC multiparois catalytiques. Leproduit obtenu a été utilisé en tant que précurseur pour l'obtention de nanoparticulesd'oxyfluorures de tungstène à l'issue d'un échange fluor-oxygène via la moléculed'hexaméthyldisiloxane.La tentative d'élaboration de structures halogénées de type nanofilamentaire à partir desNTC fonctionnalisés a été abordée en dernier lieu.

Lithium intercalate thin films have been obtained from MnPS3 starting material and characterized by the x-ray photoelectron spectroscopy technique. The regions of Mn 2p and 3p, P and S 2p, and Li 1s core levels have been investigated. The analysis of the spectra has revealed the lack of nonequivalent atoms of Mn, P and S, and Li. The presence of shake-up-type satellites at the Mn 2p and 3p core levels suggests that Li2xMn1−xPS3 is a large-gap insulating Mn compound analogously to the parent MnPS3. After lithium intercalation no remarkable shift has been observed in the binding energy positions of the investigated core levels in comparison with the corresponding MnPS3 pure compound. On these bases, we assume that only an ion transfer accompanies the lithium intercalation process.

Amorphous thin films were prepared by radio frequency magnetron sputtering from TiS 2 target under pure argon atmosphere. Two complementary techniques, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy, were used to investigate the local and electronic structure of the as-prepared sample and to study the electrochemical mechanisms occurring during the first cycle. The results exhibit that the as-prepared TiO 0 . 6 S 2 . 8 thin film is close to bulk TiS 3 [which may be viewed as Ti 4 + (S 2 - 2 )S 2 - ] with regard to the local and electronic structure. An electrochemical characterization of the film was performed. Upon lithium insertion, sulfur is first involved in the electrochemical reduction, followed by titanium. The reduction of S 2 - 2 to S 2 - is concomitant with the elongation of the distance between the two sulfur ions of the disulfide pair. At the end of the charge, the electrochemical processes appear to be reversible. This study clearly evidences the major contribution of sulfur atoms beside titanium.

Extensive investigatiofis have been carried out on various graphite intercalation compounds (GICs), but the nature of the microscopic mechanisms have not been fully understood. The transport properties of these compounds show drastic changes from the parent graphite [1] and require more theoretical investigations. As an extension of our studies on graphite ferric chloride intercalation compounds (GFeC13) of both pure and mixed stages, we report our measurements of the Hall coefficient at low magnetic fields. The graphite ferric chloride intercalation compounds of pure and mixed stages were prepared by the conventional two-zone vapour transport technique with the graphite zone at higher temperature than the intercalant zone. The temperature conditions used for the synthesis are given in Table I. This particular system was found to be environmentally stable. The samples were characterized initially by the increase in weight percentage over that of initial graphite. X-ray characterization was carried out using CoK« radiation of wavelength 0.17902 nm. The stages were identified from the (0 0 1) reflections of the X-ray diffractogram. According to the classical model of staging [2], the c axis repeat distance Ic is related to the stage number n by the simple relation

International audience; [2-(2,6-Dichloro-phenylamino)-phenyl]-acetic acid (DPAPAc) was intercalated between layers of Mg-Al hydrotalcites. Several methods of incorporation were applied: direct ion exchange of the layered double hydroxide (LDH) carbonates with the organic ions, direct synthesis by co-precipitation of metal nitrates and sodium DPAPAc, and reconstruction of the Mg-Al oxide solid solution. The LDH reconstruction method led to the highest degree of intercalation and gave rise to an enlargement of the interlayer space of about 6.7 Å, which was observed in the powder X-ray diffraction (PXRD) patterns. The new hybrid phase obtained by this method was partially intercalated, as the LDH-carbonate phase was still mainly present in the material. The characterization of the prepared samples was also achieved with X-ray photoelectron spectroscopy (XPS), which indicated changes in the environment of the elements on insertion of the organic anions. Finally, the collected data indicated that the method of reconstruction was the most effective route to the hybrid materials. © 2004 Elsevier B.V. All rights reserved.

LiMSnO 4 (M=Fe, In) compounds were synthesized by high temperature solid-state reaction method and the electrochemical studies were carried out vs. lithium metal. Lithium is reversibly intercalated and deintercalated in LiFeSnO 4 with a constant capacity of ?90 mAh/g. In situ X-ray diffraction data show that ramsdellite structure is stable for lithium intercalation and deintercalation in LiFeSnO 4. Galvanostatic discharge/charge of LiFeSnO 4 in the voltage window 0.05-2.0 V shows a reversible capacity of ?100 mAh/g. The observed capacity in LiFeSnO 4 is due to the two processes involving alloying/dealloying of Li 4.4Sn and formation/decomposition of Li 2O. In contrast, the new isotypic oxide LiInSnO 4 does not exhibit any lithium intercalation due to the absence of mixed valence for indium. Its reversible capacity is strongly dependent on the voltage window. LiInSnO 4 exhibits severe capacity fading on cycling in the voltage window 0.05-2.0 V, but shows a stable capacity of ?90 mAh/g in the voltage range 0.75-2.0 V. In situ XRD patterns of Li xFeSnO 4 (1�x�2) at various Li contents during initial lithium intercalation and deintercalation. ? 2004 Elsevier Inc. All rights reserved.

The metastable O2-LiCoO(2) phase undergoes several reversible phase transitions upon lithium deintercalation. The first transition leads to an unusual oxygen stacking in such layered compounds. This stacking is found to be stable for 0.52 < x < or = 0.72 in Li(x)()CoO(2) and is called T(#)2. We studied this phase from a structural viewpoint using X-ray and neutron diffraction (ab initio method). The new stacking derives from the O2 one by gliding every second CoO(2) slab by (1/3, 1/6, 0). The lithium ions are found to occupy very distorted tetrahedral sites in this structure. We also discuss the possibility of this T(#)2 phase to exhibit stacking faults, whose amount depends on the method used to prepare this deintercalated phase.

A layered matrix, alpha-VOPO4.2H2O was used as host species to produce a VOPO4.dimethylacetamide intercalation compound. The oxovanadium matrix and the synthesized hybrid were characterized by elemental analysis, infrared spectroscopy, thermogravimetry, X-ray diffractometry and SEM microscopy. The X-ray diffraction patterns show that the VOPO4.dimethylacetamide compound is amorphous, but can be turned lamellar after a solubilization-crystallization process. The SEM micrographs obtained for the VOPO4-dimethylacetamide hybrid matrix show that the microstructure of VOPO4.2H2O is changed after reaction, with a delamination of the oxovanadium matrix.

A chimie douce route based on successive redox and exchange reactions has allowed us to prepare new hybrid organic-inorganic materials, composed of polyacrylate macromolecules intercalated into layered double hydroxides (LDHs), deriving from Ni(OH)(2). Monomer intercalation and in situ polymerization mechanisms have appeared to be strongly dependent upon the nature of the substituting cation in the slabs. In the case of iron-based LDHs, a phase containing acrylate monomeric intercalates has been isolated and identified by X-ray diffraction and infrared spectroscopy. Second, interslab free-radical polymerization of acrylate anions has been successfully initiated using potassium persulfate. In cobalt- or manganese-based LDHs, one-step polymerization has been observed, leading directly to a material containing polyacrylate intercalate.

Zr-pillared clays were prepared from ZrOCl 2 pillaring solutions by adopting different preparative conditions. Ce 3+ ions are introduced to Zr-pillared clays by co-intercalation method. The resulting samples were characterized by XRD, TGA, N 2 sorption and UV-VIS-Diffuse reflectance spectroscopy techniques. Basal spacings in the range of 18-21 � were observed depending upon the preparative condition. TG analysis shows three weight loss regions corresponding to removal of various types of water molecules. All pillared clays show Type-I sorption isotherm typical of microporous materials. Pillaring under refluxing condition is found to have beneficial effect on the surface area and pore volume of the Zr-pillared clay. The chemical environment and location of Ce 3+ ions is studied by UV-VIS-DRS. The Ce 3+ ions are found to be present in the micropores of the Zr-pillared clays. However heat treatment at higher temperature may result in peripheral interaction between Ce 3+ ions and Zr-pillars. Catalytic activity of these pillared clays was evaluated for cyclohexanol dehydration which correlates well with the Br?nsted acidity of these materials. The Zr-Pillared clay containing Ce 3+ ions show good catalytic activity and stability with reaction time which has been ascribed to the stabilazition of the Br?nsted acidic centers.

The in-plane electrical transport and optical properties of the incommensurate intergrowth compounds (SbS)(1.15)(TiS2)(n) with n = 1, 2 have been investigated by means of measurements of the electrical resistivity, Hall coefficient and thermopower in the temperature range from 4.2 to 350 K, and by optical spectroscopy in the frequency range 1000-20000 cm(-1) at room temperature. Both the Hall effect and the thermopower indicate transport by electrons. The Hall coefficients show electron donation of about 0.57 and 0.34 of an electron per Ti atom for (SbS)(1.15)(TiS2)(n) with n = 1 and 2, respectively. The in-plane resistivity rho(ab)(T) exhibits a non-linear dependence on temperature, which can be described with the formula rho(ab)(T) = rho(0) + A(ee) (T/TF)(2) ln(T-F/T) as for a two-dimensional Fermi liquid. Fits according to the Drude model to the room temperature optical reflectivity show that the relaxation rate has a quadratic variation with frequency 1/tau(omega) similar to omega(2), also indicating Fermi-liquid behaviour with interelectronic collisions of quasiparticles, Only a small anisotropy in the ab-plane is observed in the optical spectra for the electrical field polarized parallel and perpendicular to the incommensurate direction.

We propose a self-consistent mean-field lattice-gas theory of intercalation compounds based on effective interactions between interstitials in the presence of the host atoms. In addition to short-range screened Coulomb repulsions, usually discussed in the lattice gas models, the present theory takes into account long-range effective attractions between intercalants due to elasticity of the host matrix. The mean-field phase diagram in the space of interaction parameters contains the domains of first- and second-order transitions of the order-disorder type, separated by a tricritical line, and the domain of the first-order transition of the gas–liquid-type separated from the homogeneous state by a critical line. Theoretical predictions are shown to be in qualitative agreement with the grand canonical Monte Carlo simulations. The peculiarities of the phase diagram give an insight into different types of behavior of the open circuit voltage observed in rechargeable batteries, in which an intercalation compound is used as an electrode material.

International audience; Layered double hydroxides (LDHs), containing intercalated oxometalate (Mo, W) species, were obtained by chimie douce reactions from NaNi1 − yCoyO2 cobalt substituted sodium nickelates (0.10 ≤ y ≤ 0.40). The X-ray diffraction (XRD), infrared (IR) and extended X-ray absorption fine structure (EXAFS) studies show that, in both cases, M2O72− anions (M[double bond, length as m-dash]Mo, W), made of corner-sharing tetrahedra, are intercalated. In these MO4 tetrahedra, the M-O bond with the bridging oxygen is elongated compared to the other ones, and the M-O-M angle is close to 115°. Oxygen atoms belonging to water molecules are pointing to some faces of the MO4 tetrahedra. The presence of such peculiar intercalated species, as well as the existence of an hydrogen bond network, leads to local distortions within the slabs, which entails a "turbotratic type" shape of the XRD patterns.

An intercalated material has been prepared consisting of a regular alternation of organic/inorganic layers. The films were obtained by reacting 3,4-dihydroxy-phenylalanine (dl-DOPA) with varying concentrations in a solution with freshly prepared HVO3, which suffered a oxidative polymerization/intercalation ‘in situ’ process, forming a green suspension, in which after de-hydration at room temperature produces a nanocomposite with a dark blue metallic color. Films (C8H9NO2)xV2O5·nH2O were characterized using FT–IR, ESR, powder X-ray diffraction, conductivity, and cyclic voltammetry. The X-ray diffractograms indicate that the lamellar structure of the V2O5 is preserved for low concentrations of melanin-like units (x

The application of a hybrid PAni-V2O5 cathode material in reversible lithium electrochemical cells is reported. We have studied the influence of synthesis conditions and subsequent treatments of the hybrid under oxygen in order to optimize its performance as a lithium-insertion cathode. The temperature and length of this treatment is a key parameter in determining the final specific charge of the cathode. The optimal material yielded a specific charge as high as 302 Ahkg-1 measured at low discharge rate (C/48) corresponding to the insertion of 2.72 lithium ions per formula unit (C6H4N)0.6V2O5-0.3H 2O). Higher scan rates of C/12 lead to specific capacities of 200 Ahkg-1. The thermal and electrochemical stability of the hybrid, especially in relation to the decomposition of the organic polymer and their effect on battery performance and cyclability are also discussed., This work was partially supported by CICYT (Spain) (MAT 98-0807-C02-02) and Schneider Electric. We also thank the Ministerio de Educacion y Ciencia (Spain, MEC-AECI) and CONACYT (Mexico) for a predoctoral fellowfship to M.L.C.

This thesis is concerned with several aspects of the chemistry of iron compounds. The preparation (with particular emphasis on coprecipitation and sol-gel techniques) and processing of ferrites are discussed. Chapter 2 describes the synthesis of Ni-Zn ferrites with various compositions by three methods. These methods include coprecipitation and sol-gel techniques. The Ni-Zn ferrites were characterised by powder X-ray diffactometry (PXRD), scanning electron microscopy (SEM), vibrating sample magnetometry (VSM), Mössbauer spectroscopy and resistivity measurements. The results for the corresponding ferrites prepared by each method are compared. Chapter 3 reports the sol-gel preparation of a lead borosilicate glass and its addition to Ni-Zn ferrites prepared by the sol-gel method in Chapter 2. The glass-ferrites formed were analysed by the same techniques employed in Chapter 2. Alterations in the microstructure, magnetic and electronic properties of the ferrites due to glass addition are described. Chapter 4 introduces compounds containing Fe-O-B, Fe-O-Si or B-O-Si linkages. The synthesis and characterisation of compounds containing Fe-O-B units are described. The structure of [Fe(SALEN)]2O.CH2Cl2 (17), used in attempts to prepare compounds with Fe-O-Si bonds, was determined by X-ray crystallography. Chapter 4 also details the synthesis of three new borosilicate compounds containing ferrocenyl groups, i.e. [FcBO)2(OSiBut2)2] (19), [(FcBO)2(OSiPh2)2] (20) and [FcBOSiPh3] (21). The structure of (19) was determined by X-ray Crystallographic analysis. Chapter 5 reviews the intercalation properties of the layered host compound iron oxychloride (FeOCI). Intercalation compounds prepared with the microwave dielectric heating technique are also discussed. The syntheses of intercalation compounds by the microwave method with FeOCI as host and ferrocene, ferrocenylboronic acid and 4-aminopyridine as guest species are described. Characterisation of these compounds by powder X-ray diffractometry (PXRD) and M{ssbauer spectroscopy is reported. The attempted synthesis of an intercalation compound with the borosilicate compound (19) as guest species is discussed. Appendices A-E describe the theory and instrumentation involved in powder X-ray diffractometry (PXRD), scanning electron microscopy (SEM0, vibrating sample magnetometry (VSM), Mössbauer spectroscopy and electrical resistivity measurements, respectively. Appendix F details the attempted syntheses of compounds with Fe-O-B and Fe-O-Si linkages.

Hollandite oxides of the type Bi1.7-xPbxV8O16 have been synthesized. The electrical resistivity studies show that the conductivity improves upon Pb substitution. The feasibility of Li intercalation in the system has been established. Magnetic susceptibility studies on the pure and Li intercalated phases show that except for pure Bi1.7V8O16, all phases exhibit Pauli paramagnetism. No superconductivity is encountered down to 12 K in any of the phases. ? 1998 Elsevier Science B.V. All rights reserved.

Nanocomposites obtained by the encapsulation of conducting polymers such as polyaniline and polydiphenylamine in 2H-MoS2 and 1T-TiS2 are synthesized and characterized by X-ray diffraction and infrared spectrophotometry. The synthesis consists in intercalating the layered compound with n-butyllithium and subsequent exfoliation in water and organic solvents. The nanocomposites are obtained by the adsorption of the polymers into the single-layers sulfides and posterior restacking. The X-ray diffraction measurements showed that the organic conducting polymers are encapsulated in mono and bilayers arrangement in a well-ordered fashion to produce single phase compounds.

Nanocomposites obtained by the encapsulation of conducting polymers such as polyaniline and polydiphenylamine in 2H-MoS2 and 1T-TiS2 are synthesized and characterized by X-ray diffraction and infrared spectrophotometry. The synthesis consists in intercalating the layered compound with n-butyllithium and subsequent exfoliation in water and organic solvents. The nanocomposites are obtained by the adsorption of the polymers into the single-layers sulfides and posterior restacking. The X-ray diffraction measurements showed that the organic conducting polymers are encapsulated in mono and bilayers arrangement in a well-ordered fashion to produce single phase compounds.