Titanium and vanadium oxynitride powders as pseudo-capacitive materials for electrochemical capacitors

International audienceTiOxNy and VOxNy powders have been synthesized using oxide precursors and a conventional nitridation method. It enables to control of oxygen content and surface area. The electrochemical performances of the different powders have been investigated. A strong dependence on the surface area as well as on the nature of the oxynitride has been found. A typical value of 300 μF cm−2 has been determined for VOxNy powders, while TiOxNy powders only show 50 μF cm−2. In this last case it is believed that only double layer capacitance or weak redox reactions participate in charge storage mechanism while for vanadium based oxynitrides, a thin layer below the surface (≈4 Å) is involved in charge storage via faradic reactions. VOxNy electrodes can be operated in different aqueous electrolytes, but only double layer capacitance is measured in neutral electrolytes. The highest capacitance values (≈80 F g−1) are measured in KOH and fair cycling ability is achieved when the electrochemical window is limited, thus avoiding oxidative potentials

Deposition and dielectric study as function of thickness of perovskite oxynitride SrTaO₂N thin films elaborated by reactive sputtering

International audienceThe present study concerns the deposition of perovskite oxynitride SrTaO2N films and their dielectric characterization at low frequencies. Those radio frequency sputtered thin films have been obtained under a reactive plasma (92.3 vol.% Ar / 7.7 vol.% N2) for substrate temperatures ranging from 600 to 900°C. As shown by X-rays diffraction and band-gap measurements, the deposition temperature (T S) determines the film structure and leads to films with band-gap and cell volume approaching the ones of the SrTaO2N bulk material with increased T S. The dielectric study has been performed on polycrystalline, textured and epitaxial SrTaO2N layers deposited on conductive niobium doped SrTiO3 substrates and thickness of films ranging from 30 to 900 nm. The related permittivities vary from 66.5 to 90 (@10kHz, room temperature). These low values do not point out an effect of the crystallographic strain of films, due to their thickness, on the permittivity values. The latte

Dépôt et caractérisation de couches minces diélectriques La-Ti-O-N

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Tb³⁺ doped Ga₅Ge₂₀Sb₁₀Se_65-xTe_x (x=0-37.5) chalcogenide glasses and fibers for MWIR and LWIR emissions

International audienceChalcogenide glasses with a nominal composition of Ga5Ge20Sb10Se65-xTex (x = 0, 10, 20, 25, 30, 32.5, 35, 37.5) were synthesized. Their physico-chemical properties, glass network structure and optical properties are clearly modified via the substitution of selenium by tellurium. Based on a detailed study of the Ga5Ge20Sb10Se65-xTexTex bulk glasses properties, the Ga5Ge20Sb10Se45Te20 seleno-telluride glass optimal composition has been selected for fiber drawing. The luminescence properties of Tb3+ (500 ppm) doped Ga5Ge20Sb10Se65 and Ga5Ge20Sb10Se45Te20 bulk glasses and fibers were studied. Radiative transitions parameters calculated from the Judd-Ofelt theory are compared to the experimental values. Mid-wavelength infrared emission in the range of 4.3-6.0 μm is attributed to the 7F5→7F6 transition of Tb3+ ions with a corresponding experimental lifetime of 8.9 and 7.8 ms for the selenide and seleno-telluride matrix, respectively. The 7F4→7F6emission was recorded at 3.1 μm with a good signal-to-noise ratio, evidencing a rather strong emission from the 7F4 manifold. Finally, although it was expected that the phonon energy will be lower for telluride glasses, selenide glasses are still more suitable for mid-wavelength infrared and long wavelength infrared emissions with well-defined emissions from 3.1 to 8 μm