Mechanism of lithium intercalation in titanates

First principles calculations of Li insertion in a variety of titanate structures have revealed a common mechanism underlying the intercalation behavior of these materials. The mechanism is based on the accommodation of the electron density donated upon intercalation in particular orbitals of Ti ions and is governed by a strong coupling between the structural and electronic degrees of freedom. A new predictive model is developed which relates the local structure of TiO₂ polymorphs to their phase behavior upon Li intercalation.     

Reversible intercalation of large-capacity hemoglobin into in situ prepared titanate interlayers with enhanced thermal and organic medium stabilities

The exfoliated single-layer titanate can rapidly restack and reversibly release heme protein simply by adjustment of the pH value. The composites have regularly layered structure and powdery morphology by their ideal layer-to-layer assembly, which provides the titanate nanosheet an unusual specific intercalation capacity of 5900 mg g(-1) for the protein. The bound and released proteins keep active relative to the intact protein. The hemoglobin thermal and organic solvent stabilities are improved by the protective environment of the titanate host.     

Alkali metal cation intercalation properties of titanate nanotubes

Hydrothermally synthesized titanate nanotubes show high alkali metal cation intercalation reactivity evidenced by high resolution microscopic examination, elemental mapping and profiling techniques as well as wet chemical analysis.     

Zum Intercalationsverhalten thermisch vorbelasteter Kaolinite gegenüber Hydrazinhydrat,Dimethylsulfoxid sowie Harnstoff

On the Intercalation Behaviour of Preheated Kaolinites towards Hydrazine Hydrate, Dimethyl Sulfoxide, and Carbamide The intercalation behaviour towards hydrazine hydrate, dimethyl sulfoxide, and carbamide, respectively, of partially dehydroxylated samples of a kaolin and of a clay has been studied. The intercalation activity of the named compounds decreases with increasing degree of dehydroxylation of the kaolinite component. In this respect, however, the intercalation behaviour of the three compounds is quite different. The reactivity of carbamide depends most sensibly on the thermally created lattice defects. In comparison with the well-crystallized kaolinite of the kaolin the kaolinite component of the clay is highly disordered. It is due to this disorder that not only the usual intercalation activity is reduced, but also this activity is much more sensible against thermal pretreatment of the kaolinite.     

Two phase morphology limits lithium diffusion in TiO(2)(anatase): a (7)Li MAS NMR study.

7Li magic angle spinning solid-state nuclear magnetic resonance is applied to investigate the lithium local environment and lithium ion mobility in tetragonal anatase TiO(2) and orthorhombic lithium titanate Li(0.6)TiO(2). Upon lithium insertion, an increasing fraction of the material changes its crystallographic structure from anatase TiO(2) to lithium titanate Li(0.6)TiO(2). Phase separation occurs, and as a result, the Li-rich lithium titanate phase is coexisting with the Li-poor TiO(2) phase containing only small Li amounts approximately equal to 0.01. In both the anatase and the lithium titanate lattice, Li is found to be hopping over the available sites with activation energies of 0.2 and 0.09 eV, respectively. This leads to rapid microscopic diffusion rates at room temperature (D(micr) = 4.7 x 10(-12) cm(2)s(-1) in anatase and D(micr) = 1.3 x 10(-11) cm(2)s(-1) in lithium titanate). However, macroscopic intercalation data show activation energies of approximately 0.5 eV and smaller diffusion coefficients. We suggest that the diffusion through the phase boundary is determining the activation energy of the overall diffusion and the overall diffusion rate itself. The chemical shift of lithium in anatase is independent of temperature up to approximately 250 K but decreases at higher temperatures, reflecting a change in the 3d conduction electron densities. The Li mobility becomes prominent from this same temperature showing that such electronic effects possibly facilitate the mobility.     

Intercalation of lithium into porous titanium oxide produced by anodic oxidation

Process of lithium intercalation in a 1 M anhydrous propylene carbonate solution of LiClO₄ into porous titanium oxide produced by anodic oxidation of titanium in aqueous and nonaqueous electrolytes containing fluoride ions was studied. It is shown that the mass of intercalated lithium, which determines the efficiency of the cathodic reaction of lithium titanate formation, strongly depends on the specific surface area of the oxide. The results obtained make it possible to formulate approaches to solving the problem of raising the reversible electrical capacity of a lithium power source.     

Effect of nano-barium titanate on thermal stability of ferrite filled poly-ether-ether-ketone (PEEK) composites

The reinforcement of nano-barium titanate in ferrite filled poly-ether-ether-ketone (PEEK) composites caused a shift in the decomposition temperature, at which maximum mass loss occurred, to higher side and enhancement in char yield in thermogravimetric analysis. Loss tangent and glass transition temperature of ferrite filled PEEK composites were also found to be increased with the reinforcement of nano barium titanate. The effect of nano barium titanate on the melting behaviour of ferrite filled PEEK composites was negligible. This revised version was published online in August 2006 with corrections to the Cover Date.     

The Rapid Exfoliation and Subsequent Restacking of Layered Titanates Driven by an Acid–Base Reaction

Two‐dimensional (2D) (hydro)oxide materials, that is, nanosheets, enable the preparation of advanced 2D materials and devices. The general synthesis route of nanosheets involves exfoliating layered metal (hydro)oxide crystals. This exfoliation process is considered to be time‐consuming, hindering their industrial‐scale production. Based on in situ exfoliation studies on the protonated layered titanate H_1.07Ti_1.73O₄?H₂O (HTO), it is now shown that ion intercalation‐assisted exfoliation driven by chemical reaction provides a viable and fast route to isolated nanosheets. Contrary to the general expectation, data indicate that direct exfoliation of HTO occurs within seconds after mixing of the reactants, instead of proceeding via a swollen state as previously thought. These findings reveal that ion intercalation‐assisted exfoliation driven by chemical reaction is a promising exfoliation route for large‐scale synthesis.     

Flower-like surface modification of titania materials by lithium hydroxide solution

Surface modification of titania materials to give flower-like structures has been achieved simply by the treatment in lithium hydroxide aqueous solution under mild conditions. The flower-like structured materials were characterized by X-ray diffraction, thermogravimetric analysis, and Raman scattering. The analyses indicate that the flower-like materials are composed of layered hydrous lithium titanate. It is suggested that the unique intercalation behavior of lithium ions into titania allows dissolution and re-precipitation of titania to form the flower-like structure. The obtained flower-like structure can be retained up to 700 °C, while the crystal phase transforms into Li(4)Ti(5)O(12).     

Ion exchangeable layered niobates as a noble series of photocatalysts

Some characteristic behaviors of ion-exchangeable layered niobate photocatalysts are described. The main feature of this type of photocatalysts comes from the intercalation of the reactant and the reaction proceeding at the interlayer space. In this point of view, these catalysts are regarded as “two dimensional” photocatalysts. Judging from the wide variety of these families including not only niobates but also other early transition metal oxides such as titanate, and also their unique structures, ion-exchangeable layered oxides will be an interesting subject to be used in the field of photocatalysis.     

The lithium intercalation compound Li2CoSiO4 and its behaviour as a positive electrode for lithium batteries

The electrochemical behaviour of 3 polymorphs of the lithium intercalation compound Li2CoSiO4, betaI, betaII and gamma0, as positive electrodes in rechargeable lithium batteries is investigated for the first time.     

Multiwalled Carbon Nanotubes Resist Intercalation Whereas Pyrolytic Graphite Can Exfoliate in Propylene Carbonate: Electroanalysis Without the Deleterious Effects of Intercalation for the Detection of Ammonia

A generic approach is presented allowing the sensing of electroactive species at carbon based electrodes in otherwise potentially intercalating media. Graphite electrodes are known to suffer intercalation leading to exfoliation in propylene carbonate solution containing tetra‐n‐butylammonium perchlorate as supporting electrolyte. However, we report contrasting behaviour at bamboo multiwalled carbon nanotubes, where intercalation/exfoliation does not occur, so allowing useful electroanalytical measurements to be made, in particular for the amperometric determination of ammonia.     

Potential Energy Surfaces and Charge Transfer of PAH‐Sodium‐PAH Complexes

To further understanding of the role of sodium in carbon cathode degradation in Hall–Héroult cells, potential‐energy surfaces and charge‐transfer curves are presented for finite‐size complexes of sodium intercalated between various polycyclic aromatic hydrocarbons. Calculations for lithium and potassium are included to highlight the disparate intercalation behaviour of the alkali metals in graphite intercalation compounds. Static energy barriers from DFT are used to compute macroscopic diffusion coefficients according to transition‐state theory. Comparing the calculated diffusion coefficient to experimental values from the literature sheds light on the role of lattice diffusion of sodium–graphite intercalation compounds in sodium intrusion in graphitic carbon cathodes.     

Effects of metal salts on the thermal decomposition of edta-gel precursors for ferroelectric ceramic powders

Raw chemicals such as metal nitrates and chlorides were found to affect the thermal decomposition behaviour of EDTA-gel precursors used for the production of ceramic powders. Fine, homogeneous ceramic powders were produced from nitrate solutions while chlorides gave segregated phases. In studies on the production of lead zirconate titanate (PZT) using chlorides, the segregation and loss of lead was observed and shown to be caused by the formation and evaporation of PbCl₂. Thermal analysis (DTA/TG) quantitatively proved the suggested reaction mechanism for this phase segregation. Crystallization of the desired perovskite phase of lead zirconate titanate (PZT) and barium titanate (BT) initiated at temperatures as low as 250°C in the nitrate-EDTA precursors. Water of crystallization and formation of BaCO₃ in the barium titanate precursor were suggested to account for differences in the observed decompositional behaviours of the BT and PZT precursors.     

Preparation, characterization and thermal dehydration kinetics of titanate nanotubes

Titanate nanotubes were synthesized utilizing the hydrothermal method using titanium dioxide nanoparticles. The experiments were carried out considering the process as a function of reaction temperature, time, NaOH concentration and the acidity of the washing solution. The formation of titanate nanotubes was shown to be affected strongly by variations in any parameter. The optimum conditions for the synthesis of titanate nanotubes were determined to be a reaction temperature of 190 °C, and a reaction time of 12 h, using 10 M NaOH concentration and the washing solution to have a pH of 5.5. In addition, thermogravimetric analysis (TG/DTG) was used to investigate the thermal behaviour and dehydration kinetics of titanate nanotubes. In order to better understand their thermal behaviour, the thermal analysis of bulk hydrogen trititanate was performed. The values of the apparent activation energies of the first and second dehydration stages for titanate nanotubes were 81.44 ± 15.85 and 82.69 ± 7.46 kJ mol^?1, respectively. The values of the apparent activation energies of the first, second and third dehydration stages for bulk hydrogen trititanate were 115.93 ± 5.40, 137.58 ± 6.47 and 138.97 ± 8.47 kJ mol^?1, respectively.     

Synthesis and crystal structure of AlH2P3O10.2H2O; a new structure-type for layered acid phosphates

The crystal structure of the layered acid phosphate, AlH2P3O10.2H2O, has been determined and provides a new structure-type for a series of metal phosphates with interlamellar regions likely to be highly suited to intercalation behaviour.     

A Comparison of the Nanostructure of Lead Zirconate,Lead Titanate and Lead Zirconate Titanate Sols

Sol-gel processing has been widely used for the fabrication of lead zirconate titanate (PZT) thin films. To successfully and consistently make high quality thin films for different applications, we must develop a fundamental understanding of the structures of the sols. In this study, the characters of lead titanate (PT) and lead zirconate (PZ)sols were studied by measuring the rheological properties and particle sizes in them and comparing their behaviours. The average particle sizes in unhydrolysed PT, PZ and PZT sols are 11.5, 1.0, and 6.0 nm, respectively. PT sol has the highest rate of hydrolysis. It gels at about 24 h after hydrolysis. PZ and PZT sols have a quite similar feature in hydrolysis. The reasons for the differences in the hydrolysis behaviour of the different types of sol are discussed in terms of a model which indicates that the inhomogeneous sols consist of 5 to 6 nm PT particles surrounded by much smaller PZ particles, which tend to dominate the sol behaviour.     

Contact angle measurements as a tool to investigate the filler-matrix interactions in polyurethane-clay nanocomposites from blocked prepolymer

Optically transparent polyurethane-clay nanocomposite films were prepared by dispersing 5 wt% of various commercial organo-clays in a mixture of cycloaliphatic amines used as chain extender-cross-linker of a blocked prepolymer. For the first time, vibration-induced equilibrium contact angle measurements were successfully employed to rank the selected organo-clays accordingly to their hydrophobicity order. Polymer-clay intercalation degree in the nanocomposites, as assessed from X-ray diffraction, was strongly correlated to the water-clay equilibrium contact angle. Moreover, as the clay intercalation degree increased, a decrease of the cross-linking degree of the polyurethane matrix occured.Uniaxial tensile tests under quasi-static and impact conditions, and isothermal thermogravimetric analysis were performed on both unfilled polyurethane matrix and nanocomposites. Secant tensile modulus, tensile energy to break, and thermal lifetime showed a non monotonic trend with a maximum as a function of the intercalation degree. This behaviour is discussed considering that two concomitant and contrasting effects develop as the polymer-clay intercalation degree increases: a positive improvement of the filler matrix interactions, and a negative reduction of the matrix cross-linking degree.     

Polymerisation anionique de lactones amorcees par les composes d'insertion K C24: Caracterisation des polymeres obtenus

The graphite intercalation compound K C₂₄ initiates the polymerization of caprolactone, propiolactone and pivalolactone. The resulting polycaprolactones show a double molecular weight distribution, with an important proportion of high molecular weights. The polylactones are semicrystalline; the values and the distributions of molecular weights influence behaviour in melting and crystallization.     

Analogies and differences between calcium-based and europium-based graphite intercalation compounds

An original method using lithium-based liquid alloys has been developed, allowing studies on bulk graphite intercalation compounds with calcium and europium. We showed that binary and ternary compounds belonging to graphite-lithium-calcium and graphite-lithium-europium systems are synthesized in both cases for equivalent reaction conditions but amazingly with many different structural and physical properties. Concerning CaC₆ and EuC₆, even if their 2D unit cells are hexal, their c-axis stacking sequences lead to different symmetries. Regarding kinetical data, formation mechanisms of these graphite intercalation compounds appear comparable however different, with a first common step before differenciation in the intercalation mechanism. Obviously, their physical properties are strongly different due to the nature of the intercalated metallic element. So, the different ternary compounds from these systems also show very considerable differences concerning their electronic properties: complex magnetic ordering for Eu-based ternary GIC and superconducting behaviour for Ca-based ternary GIC. However, common points are highlighted.