Phase-pure TiO2(B) with microfibrous morphology was prepared via a newly developed method from amorphous TiO2. Cyclic voltammetry evidences that Li-insertion into TiO2(B) is governed by a pseudocapacitive faradaic process, whose rate is not limited by solid-state diffusion of Li+ in a broad interval of scan rates. This unusual behavior was discussed in terms of the crystal structure of the TiO2(B) host, having freely accessible parallel channels for Li+-transport perpendicular to the (010) face. The characteristic Li-insertion electrochemistry of TiO2(B) allows re-interpretation of several previous reports, which did not consider explicitly this relation or the presence of TiO2(B) in various TiO2 materials of different origin.

The Pluronic P123 templated mesoporous TiO2 film was grown via layer-by-layer deposition and characterized by a novel methodology based on the adsorption of n-pentane. Multiple-layer depositions did not perturb the mesoporous structure significantly. Our TiO2 film was sensitized by a newly developed Ru-bipyridine dye (N945) and was applied as a photoanode in dye-sensitized solar cell. The 1-microm-thick mesoporous film, made by the superposition of three layers, showed enhanced solar conversion efficiency by about 50% compared to that of traditional films of the same thickness made from randomly oriented anatase nanocrystals.

Nanostructured titania materials were prepared from TiCl 4 via autoclaving in 10 M NaOH at 250 °C and subsequent treatment in aqueous and/or acidic media. XRD and Raman spectroscopy evidenced the presence of anatase as the main phase, but most materials contained also some XRD-silent component. Cyclic voltammograms of lithium insertion demonstrate two pairs of reversible pseudocapacitive peaks (S-peaks) in addition to the ordinary peaks of diffusion-controlled Li insertion into the anatase lattice. The occurrence of S-peaks is associated with the nanosheet-and/or nanotubular morphology of the materials. This structure developed at hydrothermal conditions via exfoliation of the layered Na + /H + titanate precursors. The S-peaks were suggested to be the signatures of quantum-size confinement in titania nanosheets. The nanosheet-containing materials are reducible by n-butyllithium to cubic LiTiO 2 (at conditions when the ordinary nanocrystalline anatase gives only the orthorhombic Li 0.5 TiO 2 ). Consequently, the electrochemical Li-storage capacity is larger compared to that of crystalline anatase. The prepared materials also show better insertion kinetics; hence, they are promising for applications in Li-ion batteries. Depending on the applied voltage, they can be charged/discharged either as ordinary Li-insertion hosts or as supercapacitors.

Six representative isotope-labeled samples of titanium dioxide were synthesized: Ti(16)O(2), Ti(17)O(2) and Ti(18)O(2), each in anatase and rutile forms. Their Raman scattering was analyzed at temperatures down to 5 K. Spectral assignment was supported by numerical simulation using DFT calculations. The combination of experimental and theoretical Raman frequencies with the corresponding isotopic shifts allowed us to address various still-open questions about the second-order Raman scattering in rutile, and the analysis of overlapping features in the anatase spectrum.

Li 4 Ti 5 O 12 ͑spinel͒ materials were prepared with Brunauer-Emmett-Teller surface areas ranging from 1.3 to 196 m 2 /g. The corresponding average particle sizes varied from ca. 1 m to ca. 9 nm. Twenty-five different materials were tested as Li insertion hosts in thin-film electrodes ͑2-4 m͒ made from a pure spinel. Trace amounts of anatase in Li 4 Ti 5 O 12 were conveniently determined by cyclic voltammetry of Li insertion. Electrodes from nanocrystalline Li 4 Ti 5 O 12 exhibited excellent activity towards Li insertion, even at charging rates as high as 250C. The charge capability at 50-250C was proportional to the logarithm of surface area for coarse particles ͑surface areas smaller than ca. 20 m 2 /g͒. With increasing charge/discharge rates, a narrowing plateau in performance was observed for materials with surface areas between ca. 20 to 100 m 2 /g. These materials can be charged/discharged nearly to the nominal capacity of Li 4 Ti 5 O 12 ͑175 mAh/g͒ within a wide range of the rates. Very small particles (surface areas Ͼ 100 m 2 /g) exhibit a growing decrease of charge capability at 50-250C. The Li-diffusion coefficients, calculated from chronoamperometry, decrease by orders of magnitude if the average particle size drops from ca. 1 m to ca. 9 nm. However, the sluggish Li ϩ transport in small particles is compensated by the increase in active electrode area. Materials having surface areas larger than ca. 100 m 2 /g also tend to show increased charge irreversibility. This could be caused by parasitic cathodic reactions, due to enhanced adsorption of reducible impurities ͑humidity͒ or the quality of the spinel crystalline lattice itself. The optimum performance of thin-film Li 4 Ti 5 O 12 electrodes is achieved, if the parent materials have surface areas between ca. 20 to 110 m 2 /g, with the maximum peak at 100 m 2 /g. Spinel oxides Li 1ϩx Ti 2Ϫx O 4 ; 0 р x р 1/3 were introduced in the early 1990s as promising zero-strain Li-insertion hosts. 1-3 The cubic lattice constant, a ͑space group Fd3m) scales with composition ͑x͒ according to Eq. 1 ͑for a in nm͒ 4The relations between composition ͑x͒ and Li-insertion thermodynamics were not studied very systematically, but the end members of the series, i.e., LiTi 2 O 4 and Li 4/3 Ti 5/3 O 4 (Li 4 Ti 5 O 12 ) exhibited the formal potential of Li insertion 1.36-1.338 V and 1.55-1.562 V, respectively. 1,5 The Li 1ϩx Ti 2Ϫx O 4 ͑spinels͒ are usually prepared by solid-state reactions of suitable Li-and Ti-containing precursors during 12-24 h at 800-1000°C. 1,2,4-11 The particle size was not systematically addressed in most cited works, but Abraham et al. 11 have reported that the solid-state reaction of TiO 2 with Li 2 CO 3 or LiOH gave at 800°C micrometer-sized product. Amatucci et al. 12,13 have recently reported on nanocrystalline Li 4 Ti 5 O 12 resulting from a hightemperature solid-state reaction of TiO 2 and Li 2 CO 3 , 12 but neither the particle size nor preparative details were specified in their works. 12,13 Alternatively, the lithium titanate spinels can also ...

The high pressure behavior of bundled 1.35Ϯ 0.1 nm diameter single wall carbon nanotubes ͑SWNT͒ filled with C 70 fullerenes ͑usually called peapods͒ has been investigated by Raman spectroscopy and compared with the corresponding behavior of the nonfilled SWNT. We show experimentally that two reversible pressureinduced transitions take place in the compressed bundle SWNT. The first transition, in the 2-2.5 GPa range, is in good correspondence with predictions of the thermodynamic instability of the nanotube circular cross section for the studied tube diameter. An interaction between the fullerenes and the tube walls is then observed at about 3.5 GPa, which evidences a progressive deformation of the tube cross section. The second transition takes place at pressures between 10 and 30 GPa, and is evidenced by two effects by a strong frequency downshift of the Raman transverse modes and the concomitant disappearance of the fullerenes Raman modes in peapods. The pressure at which the second transition takes place is strongly dependent on the nature of the pressure transmitting medium. We also report irreversible effects at high pressure as the shortening of the tubes, the formation of nanostructures and the disappearance of the C 70 Raman signal in some cases. Transmission electron microscopy studies are also reported supporting these transformations.

Nanocrystalline fibrous TiO 2 (anatase) was prepared by electrostatic spinning from ethanolic solution of Ti(IV) butoxide, acetylacetone, and poly(vinylpyrrolidone) employing the Nanospider industrial process. These titania fibers were smoothly converted into cubic titanium oxynitride, TiO x N y fibers (a = 4.1930 A ˚) during 4 h at 600 °C in ammonia atmosphere. The obtained material is convertible back into TiO 2 fibers by heat treatment in air at 500 °C. The TiO 2 fibers, which were reformed in this way, contain anatase as the main phase. Their follow-up reaction with NH 3 at 600 °C/2 h leads to a less crystalline oxynitride material with a ≈ 4.173 A ˚, which is close to that of cubic TiO. Three subsequent cycles of this transformation were demonstrated. The described conversions are specific for electrospun anatase fibers only. At the same experimental conditions, other forms of nanocrystalline anatase do not react with ammonia yielding cubic phases. An almost perfectly stoichiometric titanium nitride, TiN (a = 4.2290 A ˚) containing only 0.2 wt % O, was prepared from TiO x N y fibers in NH 3 at temperatures up to 1000 °C. This TiN material maintains the morphology of fibers and is composed of nanocrystals of a similar size as those of the precursor.

Raman spectra of electrochemically charged single-wall carbon nanotubes (HiPco) were studied by five different laser photon energies between 1.56 and 1.92 eV. The bands of radial breathing modes (RBM) were assigned to defined chiralities by using the experimental Kataura plot. The particular (n,m) tubes exhibit different sensitivity to electrochemical doping, monitored as the attenuation of the RBM intensities. Tubes which are in good resonance with the exciting laser exhibit strong doping-induced drop of the RBM intensity. On the other hand, tubes whose optical transition energy is larger than the energy of an exciting photon show only small changes of their RBM intensities upon doping. This rule presents a tool for analysis of mixtures of single-walled carbon tubes of unknown chiralities. It also asks for a re-interpretation of some earlier results which were reported on the diameter-selectivity of doping. The radial breathing mode in strongly n- or p-doped nanotubes exhibited a blue-shift. A suggested interpretation follows from the charging-induced structural changes of SWCNTs bundles, which also includes a partial de-bundling of tube ropes.