Societe CESIGMA signals and systems

Sainte-Foy-lès-Lyon, France

Societe CESIGMA signals and systems

Sainte-Foy-lès-Lyon, France
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Taoufyq A.,CNRS Institute Materials Microelectronics nanosciences of Provence | Taoufyq A.,University Ibn Zohr | Taoufyq A.,CEA Cadarache Center | Taoufyq A.,Societe CESIGMA signals and systems | And 10 more authors.
Journal of Materials and Environmental Science | Year: 2014

The aim of this study was to investigate the photocatalytic activity of polycrystalline phases of bismuth tungstatesof formula Bi2-xCexWO6 with x = 0, 0.5 and 1. The doped or pure bismuth tungstate phases were prepared by coprecipitation method and the obtained precursors were submitted to different calcination temperatures 300°C, 400°C, 600°C and 900°C. The Bi2-xCexWO6powders were characterized by X-ray diffraction, and the orthorhombic structure of Bi2WO6 was confirmed. The presence of a two-phase system in the case of substituted samples (x=0.5 and 1) was observed. All doped or substituted samples Bi2-xCexWO6 presented a monoclinic phase, coexisting with a ceria phase CeO2.The photocatalytic activity of the as-prepared samples was studied by irradiating aqueous solutions of Rhodamine B, associated with Bi2WO6 additives having variable crystallite sizes. The photocatalytic activity of such bismuth tungstates increased as the crystallite sizes decreased.The bismuth tungstates Bi2-xCexWO6 (x=0.5 and 1) were studied in the same experimental conditions: the photocatalytic activity appeared as being very low.


Taoufyq A.,CNRS Institute Materials Microelectronics nanosciences of Provence | Taoufyq A.,University Ibn Zohr | Taoufyq A.,CEA Cadarache Center | Taoufyq A.,Societe CESIGMA signals and systems | And 9 more authors.
Journal of Materials and Environmental Science | Year: 2014

In the present work, we investigate the structural and luminescence properties of the bismuth tungstate Bi2WO6. This phase is interesting because of its electrical [1], photocatalytic [2] and luminescence [3] properties. Polycrystalline samples were elaborated using a coprecipitation technique followed by a calcination process at different temperatures (300, 400, 600 and 900°C). The samples were characterized by X-ray diffraction, scanning and transmission electron microscopy (SEM, TEM) analyses. The space group Pca21 has been confirmed for this phase. The transmission electron microscopy analysis showed that this structural configuration is valid at a very low scale. Crystal cell parameters and cell volume depend on elaboration temperature. Luminescence experiments of these polycrystalline samples were performed under UV-laser light irradiation. Luminescence intensities depend on the elaboration conditions.


Taoufyq A.,CNRS Institute Materials Microelectronics nanosciences of Provence | Taoufyq A.,University Ibn Zohr | Taoufyq A.,CEA Cadarache Center | Taoufyq A.,Societe CESIGMA Signals and Systems | And 8 more authors.
Journal of Solid State Chemistry | Year: 2013

The bismuth tungstate Bi2WO6 was synthesized using a classical coprecipitation method followed by a calcination process at different temperatures. The samples were characterized by X-ray diffraction, simultaneous thermogravimetry and differential thermal analysis (TGA/DTA), scanning and transmission electron microscopy (SEM, TEM) analyses. The Rietveld analysis and electron diffraction clearly confirmed the Pca21 non centrosymmetric space group previously proposed for this phase. The layers Bi2O 2 2+ and WO4 2- have been directly evidenced from the HRTEM images. The electrical properties of Bi 2WO6 compacted pellets systems were determined from electrical impedance spectrometry (EIS) and direct current (DC) analyses, under air and argon, between 350 and 700 °C. The direct current analyses showed that the conduction observed from EIS analyses was mainly ionic in this temperature range, with a small electronic contribution. Electrical change above the transition temperature of 660 °C is observed under air and argon atmospheres. The strong conductivity increase observed under argon is interpreted in terms of formation of additional oxygen vacancies coupled with electron conduction. © 2013 Elsevier Inc. All rights reserved.


Taoufyq A.,CNRS Institute Materials Microelectronics nanosciences of Provence | Taoufyq A.,CEA Cadarache Center | Taoufyq A.,Societe CESIGMA Signals and Systems | Ait Ahsaine H.,University Ibn Zohr | And 7 more authors.
Journal of Solid State Chemistry | Year: 2013

The bismuth tungstate Bi2WO6 was synthesized using a classical coprecipitation method followed by a calcination process at different temperatures. The samples were characterized by X-ray diffraction, simultaneous thermogravimetry and differential thermal analysis (TGA/DTA), scanning and transmission electron microscopy (SEM, TEM) analyses. The Rietveld analysis and electron diffraction clearly confirmed the Pca21 non centrosymmetric space group previously proposed for this phase. The layers Bi2O2 2+ and WO4 2- have been directly evidenced from the HRTEM images. The electrical properties of Bi2WO6 compacted pellets systems were determined from electrical impedance spectrometry (EIS) and direct current (DC) analyses, under air and argon, between 350 and 700°C. The direct current analyses showed that the conduction observed from EIS analyses was mainly ionic in this temperature range, with a small electronic contribution. Electrical change above the transition temperature of 660°C is observed under air and argon atmospheres. The strong conductivity increase observed under argon is interpreted in terms of formation of additional oxygen vacancies coupled with electron conduction. © 2013 Elsevier Inc.

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