International audienceTitania nanoparticles are widely studied for photoconversion processes where combining high surface area, charge transport properties, and chemical stability is meaningful. To enhance the conversion efficiency, new compounds with reduced band gap are actively researched to utilize the visible part of the solar spectrum. Some narrowing of the gap can be observed when doping titania with nitrogen, leading to suboxide species. Using laser pyrolysis, we have synthesized for the first time true titanium monoxide TiO nanoparticles with a rock-salt crystallographic structure. The as-formed nanoparticles of black color contain carbon which can be removed by soft annealing under air while maintaining the presence of the TiO phase. These nanoparticles exhibit a very large shift of the light absorption threshold, up to 1.2 eV toward visible range, compared to the anatase form of titania. XPS analysis allows discussion of the role of nitrogen in the formation of this phase and its optical properties. First results indicate efficient photoactivity under UV and visible irradiation

TiO 2 nanoparticles show interesting catalytic and optical properties and are therefore highly demanded for several applications. In this paper, we show that pure and N-doped TiO 2 powders with an average diameter as low as 8 nm can be synthesized by laser pyrolysis, with the use of an aerosol of TTIP (titanium tetraisopropoxide) as the main precursor sensitized by C 2 H 4 . We demonstrate the possibility to control the anatase/rutile phase ratio over a large range, which was not achieved before, by tuning the experimental parameters.

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The temperature dependence of the optical spectra of two La2−xSrxCuO4 single crystals was investigated for both in-plane and out-of-plane directions. For the underdoped (x = 0.08) single crystal, the in-plane optical conductivity that was analysed by a generalized Drude formalism shows a suppression of the scattering rate 1/τ(ω) and an increased effective mass m* as the temperature decreases at low frequencies. Since this behaviour can be explained by the pseudogap effect, it is concluded that the pseudogap is not present at the optimal doping (x = 0.15). This result is confirmed by the c-axis optical conductivity, which decreases only for the underdoped single crystal. The absence of the pseudogap at the optimal composition is in accord with the quantum critical point model and it can explain the phase diagram of high-temperature superconductors.

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