Philippe Barboux

Chemical and electrochemical insertion of Na into the spinel λ-MnO2 phase

Abstract We report the electrochemical reaction of sodium with the spinel, λ-MnO 2 . Cycling data show that the room temperature reaction of Na induces an irreversible phase transformation to a new structure of Na x MnO 2 that can reversibly cycle 0.6 Na atoms per Mn atom. This compound can also be obtained at room temperature by reacting the spinel phase with a solution of sodium iodine under reflux in acetonitrile. Upon heating, this low temperature phase changes to a second polytype above 100°C, at a temperature that depends on the heating rate, and then to a third polytype above 600°C. The phase formed above 600°C is identified as the three-dimensional phase Na 0.44 MnO 2 . The low temperature and medium-temperature phases are probably layered phases, with structure related to that of Na 0.7 MnO 2 .

Diffusion protonique dans les xerogels de pentoxyde de vanadium

Abstract Vanadium pentoxide gels appear to be mixed conductors. Electronic conduction arises from the hopping of small polarons between vanadium ions in different valence state. It mainly depends on the V(IV) / V(V) ratio. Ionic conduction arises from the diffusion of protons through the gel. A very high a.c. conductivity is observed in the V 2 O 5 , 1.6 H 2 O xerogel (≈10 −2 Ω −1 cm −1 at 300K). The ionic conductivity strongly depends on the amount of water in the V 2 O 5 , nH 2 O gel. It decreases quite fast when the water content decreases (≈10 −5 Ω −1 cm −1 at 300K for V 2 O 5 , 0.5 H 2 O). The gel should actually be considered as a polyvanadic acid hydrate in which lamellar oxide particles are held together by water layers as in the H.U.P. protonic conductor.

Metallic clusters in nonstoichiometric gallium oxide films

Oxygen deficient gallium oxide films have been grown by pulsed-laser deposition. Depending on the growth conditions (oxygen pressure and laser power density), amorphous and insulating or partially crystalline and conducting gallium oxide films can be obtained. For very large oxygen deficiencies (Ga2O2.3), the oxide is not stable, and a phase separation leads to metallic Ga nanoparticles embedded in a stoichiometric Ga2O3 matrix. The resistivity measurements evidence the melting and freezing of Ga metallic nanoparticles in addition to their superconducting transition at low temperature. Due to small size both transitions are shifted as compared to the bulk properties.

Some Factors Affecting the Removal of Lead(II) Ions from Aqueous Solution by Porous Calcium Hydroxyapatite: Relationships between Surface and Adsorption Properties

A porous hydroxyapatite (p-HAp) was prepared and employed for the removal of lead(II) ions at different concentrations from aqueous solution to determine the adsorption properties of p-HAp and compare them with those of a commercial hydroxyapatite (CAp) sample. The kinetic data obtained indicated that the adsorption performances of the adsorbents depended both on their specific surface area and crystallinity. Complexation of the Pb(II) ion on the adsorbent surface favoured the dissolution of hydroxyapatites characterized by a Ca/Pb molar ratio in the 0.85–1.5 range. The maximum adsorption capacity of p-Hap for Pb(II) ions at 30 ± 2°C was 2.30 mmol/g relative to 1.38 mmol/g for the commercial compound Cap at the same temperature. The higher capacity of p-HAp was explained in terms of its porosity and crystallinity. The Pb(II) ions sorption results could be modelled by the Langmuir and Freundlich isotherms.

Growth and characterization of nasicon thin films by the laser ablation method

Abstract Thin films of nasicon structure have been grown from NaM2(PO4)3 (M = Ti and Zr) targets onto silicon substrates by the laser ablation method. By the complementary use of electron microscopy, Rutherford backscattering spectrometry and X-ray diffraction techniques, the surface morphology of the deposited films, their composition and their crystalline structure have been studied as a function of the main growth conditions. Titanium-based composition yields smooth films that can only be crystallized by post-deposition high temperature annealing in oxygen or air. Zirconium-based films are directly crystallized during the deposition process, but exhibit a rough morphology associated to an important ‘splashing effect’ during the laser irradiation of the Zr-based target. Mixtures of Ti and Zr in the target lead to smooth in situ partly crystallized films.

Study of titanium phosphate gels and their application to the synthesis of KTiOPO4 films

Phosphoric acid esters PO(OR)3–x(OH)x(with 0<x<3 and R = Et, Bu, Pri, 2-methylbutane) have been studied as precursors for polycondensation reactions with titanium alkoxides. These precursors are easily synthesized by reaction of P2O5 with alcohols. Both the POH : Ti ratio and the hydrolysis ratio (H2O : Ti) have an effect on the condensation and gelation. Also, thermolysis of phosphate esters of tertiary alcohols causes the in situ generation of free H3PO4 and the condensation of titanium phosphate. The precursors and the colloidal solutions have been characterized through 31P nuclear magnetic resonance (NMR) and dynamic light scattering. The use of these colloidal solutions for the thin-film synthesis of KTiOPO4 is demonstrated.

Synthesis of gels in the system Na2O−ZrO2−SiO2

Gels have been synthesized in the SiO2−Na2O−ZrO2 system and calcined at various temperatures up to 700°C. They have been studied by infrared absorption spectroscopy. The position of the asymmetric stretching frequency of the SiO4 unit is used as a tracer of the homogeneity. It is shown that sodium increases the solubility of zirconium in the silica matrix as already observed in fused glasses.

Colloidal processing of PbZr1–x TixO3 thin films

The synthesis of PbZr1-x TixO3(0 < x < 1) perovskite films from solution has been investigated. Colloidal solutions have been obtained using lead acetate and metal butoxides. The role of chemical modifiers such as acetylacetone (acac) and of the hydrolysis ratio are described. Both have an effect on the gelation and on the behaviour during thermal decomposition (DSC–TG). The growth of the colloidal particles (studied by light scattering) and the thermal decomposition of the xerogels have been studied as a function of x in order to compare the reactivities of the precursors. Sols yielding good Theological properties as well as a low densification temperature (680 °C) have been prepared. They allow the synthesis of thin ferroelectric films by the spin-coating technique.

Sol-gel chemistry for nonlinear optics

Nonlinear optical materials have been synthesized via the sol-gel route. A chemical control of the reactivity of molecular precursors toward hydrolysis and condensation allows the deposition of transparent thin or thick films. Potassium titanyl phosphate (KTP) can be better synthesized from phosphoester precursors [PO(OH)3-x(OR)x] rather than phosphoric acid [PO(OH)3] or phosphate esters [PO(OR)3]. These precursors lead to crystalline transparent KTP thin films around 600 degree(s)C. Organic molecules for nonlinear optics can be embedded into an oxide sol-gel matrix. Second harmonic generation has been obtained after poling with thick films in which organic chromophores are chemically bonded to the oxide backbone via the use of functionalized silicon alkoxide precursors.

Lithium Battery Technologies: From the Electrodes to the Batteries

Abstract The metallic lithium is principally used in manufacturing ceramics, specialty glass (29%), rechargeable batteries (27%), high-temperature grease, continuous castings, polymers, aluminum alloys, and pharmaceuticals. Due to the huge increase of energy demand, the quantity of lithium for battery application is supposed to augment in the next future decades. It is then important to know the state of the art of lithium-ion batteries (LiBs). This chapter presents current LiB technologies with a particular focus on two principal components—positive and negative electrode materials. The positive electrode materials are described according to their crystallographic structure: layered, olivine, and spinel and the negative electrodes are classified according to their reactivity with lithium: intercalation, conversion, and alloying type materials. Some perspectives related to new materials for improved, higher energy density LiBs are presented. The electrode surface chemistry related to electrode/electrolyte interphase reactions, one of the most important factors influencing the electrochemical performance of LiBs, is also reported.