Nouveaux tantalates ferroélectriques de type bronze quadratique de tungstène : de la structure aux propriétés physiques

Ce travail concerne la synthèse et la caractérisation de nouveaux matériaux ferroélectriques de structure de type bronze quadratique de tungstène (TTB) à base de plomb et de tantale. A l'aide de calculs théoriques, une corrélation entre température de Curie et liaison chimique a été mise en évidence. Les céramiques étudiées présentent en outre d'autres caractéristiques telles qu'un comportement de type relaxeur ferroélectrique et/ou une relaxation hyperfréquence et/ou une conductivité ionique. D'importants moyens expérimentaux (mesures diélectriques en large gamme de fréquence, mesures par spectroscopie d'impédance, diffraction des rayons X, affinements structuraux, spectroscopie Raman) et théoriques (calculs basés sur la méthode de Hückel Etendue et calculs combinatoires) nous ont permis d'établir des relations étroites entre structure et propriétés physiques. L'ensemble des résultats décrits dans cette thèse constitue une contribution à l'étude des matériaux ferroélectriques de structure de type TTB. Ils ont montré la grande variété des paramètres sur lesquels il est possible d'agir afin d'optimiser les compositions en vue d'une application spécifique.This work deals with the synthesis and the characterization of new ferroelectric materials with tetragonal tungsten bronze type structure containing lead and tantalum. By the way of theoretical calculations, a correlation between Curie temperature and chemical bonding was evidenced. Moreover, ceramics studied present others features such as a relaxor behavior and/or a high frequency relaxation and/or an ionic conductivity. With the assistance of experimental means (dielectric measurements over a wide range of both frequency and temperature, complex impedance spectroscopy measurements, X-ray diffraction analysis, structure determinations, Raman spectroscopy) and theoretical ones (EHTB and combinatorial calculations) relations between structure and physical properties were established. All results described constitute a contribution to the study of ferroelectric materials with TTB structure. They point out the wide range of parameters which can be modified to optimize a composition for a specific application

Nouveaux tantalates ferroélectriques de type bronze quadratique de tungstène : de la structure aux propriétés physiques

Ce travail concerne la synthèse et la caractérisation de nouveaux matériaux ferroélectriques de structure de type bronze quadratique de tungstène (TTB) à base de plomb et de tantale. A l'aide de calculs théoriques, une corrélation entre température de Curie et liaison chimique a été mise en évidence. Les céramiques étudiées présentent en outre d'autres caractéristiques telles qu'un comportement de type relaxeur ferroélectrique et/ou une relaxation hyperfréquence et/ou une conductivité ionique. D'importants moyens expérimentaux (mesures diélectriques en large gamme de fréquence, mesures par spectroscopie d'impédance, diffraction des rayons X, affinements structuraux, spectroscopie Raman) et théoriques (calculs basés sur la méthode de Hückel Etendue et calculs combinatoires) nous ont permis d'établir des relations étroites entre structure et propriétés physiques. L'ensemble des résultats décrits dans cette thèse constitue une contribution à l'étude des matériaux ferroélectriques de structure de type TTB. Ils ont montré la grande variété des paramètres sur lesquels il est possible d'agir afin d'optimiser les compositions en vue d'une application spécifique.This work deals with the synthesis and the characterization of new ferroelectric materials with tetragonal tungsten bronze type structure containing lead and tantalum. By the way of theoretical calculations, a correlation between Curie temperature and chemical bonding was evidenced. Moreover, ceramics studied present others features such as a relaxor behavior and/or a high frequency relaxation and/or an ionic conductivity. With the assistance of experimental means (dielectric measurements over a wide range of both frequency and temperature, complex impedance spectroscopy measurements, X-ray diffraction analysis, structure determinations, Raman spectroscopy) and theoretical ones (EHTB and combinatorial calculations) relations between structure and physical properties were established. All results described constitute a contribution to the study of ferroelectric materials with TTB structure. They point out the wide range of parameters which can be modified to optimize a composition for a specific application

Nouveaux tantalates ferroélectriques de type bronze quadratique de tungstène : de la structure aux propriétés physiques

This work deals with the synthesis and the characterization of new ferroelectric materials with tetragonal tungsten bronze type structure containing lead and tantalum. By the way of theoretical calculations, a correlation between Curie temperature and chemical bonding was evidenced. Moreover, ceramics studied present others features such as a relaxor behavior and/or a high frequency relaxation and/or an ionic conductivity. With the assistance of experimental means (dielectric measurements over a wide range of both frequency and temperature, complex impedance spectroscopy measurements, X-ray diffraction analysis, structure determinations, Raman spectroscopy) and theoretical ones (EHTB and combinatorial calculations) relations between structure and physical properties were established. All results described constitute a contribution to the study of ferroelectric materials with TTB structure. They point out the wide range of parameters which can be modified to optimize a composition for a specific application.Ce travail concerne la synthèse et la caractérisation de nouveaux matériaux ferroélectriques de structure de type bronze quadratique de tungstène (TTB) à base de plomb et de tantale. A l'aide de calculs théoriques, une corrélation entre température de Curie et liaison chimique a été mise en évidence. Les céramiques étudiées présentent en outre d'autres caractéristiques telles qu'un comportement de type relaxeur ferroélectrique et/ou une relaxation hyperfréquence et/ou une conductivité ionique. D'importants moyens expérimentaux (mesures diélectriques en large gamme de fréquence, mesures par spectroscopie d'impédance, diffraction des rayons X, affinements structuraux, spectroscopie Raman) et théoriques (calculs basés sur la méthode de Hückel Etendue et calculs combinatoires) nous ont permis d'établir des relations étroites entre structure et propriétés physiques. L'ensemble des résultats décrits dans cette thèse constitue une contribution à l'étude des matériaux ferroélectriques de structure de type TTB. Ils ont montré la grande variété des paramètres sur lesquels il est possible d'agir afin d'optimiser les compositions en vue d'une application spécifique

Nouveaux tantalates ferroélectriques de type bronze quadratique de tungstène (de la structure aux propriétés physiques)

BORDEAUX1-BU Sciences-Talence (335222101) / SudocSudocFranceF

Synthesis, characterisation and evaluation of porous materials for the adsorption of carbon dioxide

In this work, mesoporous oxides, namely silica, titania and zirconia were synthesised using a triblock copolymer as structure directing agent. Further, the silica and the titania materials were functionalised with different aminosilane molecules. Characterisation of the prepared materials was carried out using various methods including nitrogen sorption, ATR infrared spectroscopy and X-ray diffraction. The materials were tested for their carbon dioxide adsorption properties using mainly microcalorimetry. In-situ infrared measurements and theoretical DFT calculations were carried out to help understand the microcalorimetric adsorption results in certain cases. With respect to the different carbon dioxide adsorption, it was highlighted that the functionalisation of amine sites on silica materials significantly improved the adsorption capacities. A comparison of the different oxides has shown that the adsorption properties mainly depend on the strength of the metal-oxygen bond within the oxides but also on the textural characteristics, such as porosity of the investigated materials.Dans ce travail, des oxydes mesoporeux, tels que silice, oxyde de titane et oxyde de zircone ont été synthétisés en utilisant un copolymère à triblock comme agent structurant. De plus, la silice et l oxyde de titane ont été fonctionnalisés avec différentes molécules d'aminosilane. La caractérisation des matériaux préparés a été effectuée par diverses méthodes, telles que la sorption d'azote, la spectroscopie infrarouge (ATR) et la diffraction des rayons X. Les matériaux ont été examinés pour leurs propriétés d'adsorption du dioxyde de carbone utilisant principalement la microcalorimétrie. Dans certains cas, des mesures de spectroscopie IR in-situ et des calculs théoriques de DFT ont été effectués pour mieux comprendre les résultats obtenus par microcalorimétrie d adsorption. En ce qui concerne les différentes propriétés d'adsorption nous avons mis en évidence que la functionalisation des emplacements d'amine sur les matériaux de silice a amélioré de manière significative les capacités d'adsorption. Une comparaison des différents oxydes a confirmé que les propriétés d'adsorption dépendent principalement de la force du lien du métal-oxygène dans les oxydes mais également des caractéristiques de texture, telles que la porosité.AIX-MARSEILLE1-BU Sci.St Charles (130552104) / SudocSudocFranceF

Redox Behavior of Nanostructured Molybdenum Oxide-Mesoporous Silica Hybrid Materials

Encapsulation of molybdenum oxide MoO3 into ordered mesoporous silica materials is demonstrated using different synthetic routes. Either supramolecular polyoxometalates of the Müller type or Na 2 Mo O 4 were used as precursors. Molybdenum oxide (MoO3)-silica hybrid materials were characterized using nitrogen-sorption experiments, transmission electron microscopy, small-angle X-ray scattering, and infrared spectroscopy. Under reducing conditions, the hybrid materials undergo an electrochromic transition from colorless or slightly yellow to blue without any leaching of Mo species from the materials. The electrochromic response, which is fully reversible, is caused by a transition from MoVI to a mixed valence MoVI/MoV molybdenum oxide encapsulated in the pores. The reduction process was studied using in situ electron spin resonance (ESR) and UV/vis absorption measurements. Materials of different pore sizes were used, and it was found that pore size effects the kinetics of the reaction

In situ study of electrochromic properties of self-assembled TiO2 nanotubes

International audienceElectrochromical properties of anodic self-assembled nanotubes were investigated. It was found that amorphous titania nanotubes were able to insert H+ ions in a highly reversible manner. Coloration of the TiO2 nanotubes occurred at potentials below -0.5 V vs. Ag/AgCl in 1M (NH4)(2)SO4 aqueous solution. The proton insertion reaction probably leads to the formation of a Ti3+/Ti4+ solid solution in the amorphous titania electrode, as was shown by the analysis of the derivative curve. The nanotubular titania electrode shows reasonable color efficiency when compared with other electrochromic materials and it is a promising candidate for the fabrication of low-cost interdigitated electrochromic devices. (C) 2012 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved

Stable silver nanoparticles immobilized in mesoporous silica

Silver nanoparticles have been produced by -irradiation of silver solution in optically transparent inorganic mesoporous silica. The reduction of Ag+ within the matrix is brought about by hydrated electrons and hydroalkyl radicals generated during the radiolysis of the 2-propanol solution. The particles formed within the silica matrix were studied by electron microscopy, nitrogen sorption measurements, and absorption spectroscopy. The particles were mostly confined and dispersed in the pores of the mesoporous hosts. Absorption spectra show that the mean Ag clusters size increases with the irradiation dose. At high dose, agglomerated large particles are formed. In contrast, at a given dose, the effect of the dose rate has been clearly demonstrated to lower the cluster size. The silver particles within the silica matrix are stable in the presence of oxygen for at least several months

Properties of Sn-doped TiO2 nanotubes fabricated by anodization of co-sputtered Ti-Sn thin films

International audienceSelf-organized Sn-doped TiO2 nanotubes (nts) were fabricated for the first time, by anodization of co-sputtered Ti and Sn thin films. This nanostructured material was characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, UV-vis spectroscopy and transmission electron microscopy. Due to their remarkable properties, Sn-doped TiO(2)nts can find potential applications in Li-ion microbatteries, photovoltaics, and catalysis. Particularly, the electrochemical performance as an anode material for Li-ion microbatteries was evaluated in Li test cells. With current density of 70 mu A cm(-2) (1C) and cut-off potential of 1V, Sn-doped TiO(2)nts showed improved performance compared to simple TiO(2)nts, and differential capacity plots revealed that the material undergoes full electrochemical reaction as a Rutile-type TiO2. (C) 2011 Published by Elsevier Ltd