Le marché de l’éclairage est un marché de masse à diffusion large en pleine mutation face aux nouvelles contraintes environnementales. Il s’inscrit dans une démarche de préservation de l’environnement avec une volonté européenne de voir sa consommation énergétique réduite de 20% d’ici 2020. Les luminophores jouent un rôle prépondérant dans les performances des systèmes d’éclairage utilisant comme sources d’excitations des LEDs bleues ou UV, ou encore un plasma (Xe-Ne), où ils permettent de convertir les photons incidents (VUV, UV ou bleus) en lumière visible. Dans le cadre de cette thèse, nous nous sommes intéressés à la production de lumière blanche. Pour obtenir une couleur la plus proche du blanc idéal et répondant aux mieux au cahier des charges de l’éclairage domestique, une amélioration des performances des luminophores utilisés classiquement est nécessaire. Au cours de ces travaux nous avons porté notre attention sur deux aluminates de formulations Y3Al5O12 dopé Ce3+ (YAG :Ce) et BaMgAl10O17 dopé Eu2+ (BAM :Eu). L’aspect novateur repose d’une part sur la synthèse de ces luminophores sous forme de nanoparticules par des voies de synthèse originales (la voie solvothermale et la combustion assistée par micro-ondes respectivement) et d’autre part sur leur mise en forme (revêtements composites « luminophores/polymère »). Plusieurs techniques expérimentales (DRX, IR, Mössbauer, aimantation, MEB, MET,…) ont été utilisées afin de caractériser leurs propriétés structurales et morphologiques. L’étude des performances optiques de ces luminophores enregistrées sous excitations bleue, UV et/ou VUV nous a permis de mettre en évidence leur utilisation potentielle dans les nouveaux dispositifs d’éclairage : associés à d’autres luminophores (rouge pour le YAG :Ce; rouge et vert pour le BAM :Eu) en proportions adéquates, il est possible de générer de la lumière blanche présentant les propriétés escomptées. / Lighting market is a widespread distribution mass market undergoing radical transformation faced with new environmental restrictions. It fits into an environmental protection approach with a European will to reduce by 20% its energy consumption by 2020. Phosphors play a key role on performances of lighting devices where, combined with LEDs (blue or UV) or plasma (Xe-Ne) excitations, they provide visible light. In this work, we have focused on the generation of white light. In order to obtain a color closest to ideal white and meeting with the specifications of domestic lighting, it is necessary to improve the performances of traditional phosphors. Two aluminates have been investigated: Ce3+ doped Y3Al5O12 (YAG :Ce) and Eu2+ doped BaMgAl10O17 (BAM :Eu). On the one hand, innovation is based on unconventional synthesis methods allowing the preparation of nanostrutured phosphors (solvothermal and microwave induced solution combustion syntheses respectively) and on the other hand on their shaping (composite coatings « phosphors/polymer »). Structural and morphological features have been studied by means of several tools (XRD, IR, Mössbauer, magnetization, SEM, TEM,…). Finally, the optical properties of phosphors recorded upon blue, UV and/or VUV excitations have evidenced that they are suitable for applications in new lighting devices: their combination with other phosphors (red for YAG:Ce; red and green for BAM:Eu) in appropriate proportions allows producing white light with the required specifications.

Les nanomatériaux sont de plus en plus utilisés dans de nombreusesapplications, que cela soit pour la catalyse, la coloration, l’optique, etc. Pour optimiser leurutilisation, il est nécessaire de mieux comprendre les réactions et interactions ayant lieu à ceséchelles. Cette thèse se propose d’essayer d’explorer les liens entre conditions de synthèse,morphologie de particules, et propriétés de celles-ci. En particulier, nous avons opté pourl’étude d’un matériau modèle : l’oxyde de cérium (IV). Les nanoparticules de CeO2 ont étéobtenues par voie de synthèse solvothermale assistée par chauffage micro-ondes. Lesmorphologies des nanoparticules de CeO2 étudiées ont été : les cubes, les octaèdres et lesbâtonnets, et nous avons essayé de fournir une explication à leur obtention par la voie desynthèse utilisée. De l’or a ensuite été déposé en surface des ces nanoparticules de CeO2 etétudié par une combinaison d’études par Microscopie Électronique en Transmission et demodélisations numériques. / Nanomaterials are more and more used in various situations, such as catalysis,color, optics, etc. To optimize their use, it is necessary to better understand reactions andinteractions taking place at these scales. This PhD thesis aims at exploring the links betweensynthesis conditions, particle morphology and their properties. In particular, we chose a tostudy a model-material: cerium (IV) oxide. CeO2 nanoparticles have been obtained bymicrowave-heating assisted solvothermal synthesis. Morphologies obtained and studied havebeen: cubes, octahedrons and rods. We tried to to give an explanation on how these synthesesallowed the formation of such morphologies. Gold has then be deposed on the surface of theseCeO2 nanoparticles, and studied by a combination of Transmission Electron Microscopystudies, and computer modelizations.

Increased demand of power, limited fuel resources and environmental concerns have recently prompted a huge thrust on research areas of alternative energy and photovoltaics have been hailed as energy source for future. Particularly, third generation solar cell configurations like dye-sensitized solar cells and quantum dot Schottky barrier solar cells have drawn more attention because of their ease of processability, cheap cost with decent performance, low payback time and portability. Quantum dots are very attractive materials as sensitizers because of their size dependent bandgap tunability, increased oscillator strength and hence higher absorption coefficient, possibility of multiple exciton generation and photochemical robustness. Hence syntheses of quantum dot based hybrid nanostructures have received huge attention among researchers for using it quantum dot sensitized solar cell configuration. This dissertation can be divided in two parts. In the first part two different methods have been reported to prepare interconnected mesoporous nanostructures of wide band gap semiconductors like TiO2 and ZnO which is very important in providing high surface area for absorption or attachment of the sensitizers. In the second part, methods have been developed to establish direct contacts between quantum dots and wide bandgap substrates without molecular linkers which are expected to increase the electron injection rate from quantum dots to TiO2/ZnO. The entire thesis based on the results and findings obtained from the present investigation is organised as follows: Chapter-I provides a general introduction on the working principle of different type of solar cells and then gives a detailed description of the structure and electronic process of dye sensitised solar cells. Then, benefits of quantum dots as sensitizer over dye molecules has been discussed followed by the modification needed in case of quantum dot sensitized solar cells. Chapter-II deals with the materials and methods which essentially gives the information about the materials used for the synthesis and the techniques utilized to characterize the materials chosen for the investigation. Chapter-III describes a hybrid sol-gel combustion technique to synthesize large quantities of highly crystalline and phase-pure anatase powder in a single step. Titanium isopropoxide reacts with oleic acid to form a viscous liquid (oxocarboxoalkoxide) which undergoes non-hydrolytic polycondensation to form TiO2 during combustion. Oleylamine takes part in formation of reverse micelle which expands during combustion giving rise to porous interconnected membrane like microstructure of pore size ~5 nm, BET surface area of ~100 m2/g and porosity of ~ 48%. More importantly, this porous powder having a pre-existing network can be used to form thicker film by doctor blade technique from its paste and at the same time is expected to have better transport properties due to its less particulate nature. Chapter-IV presents a general method to prepare mesoporous structure from rod-like morphologies by partial sintering of a green pellet. Material having inherent anisotropy in their crystal structure tends to grow in a particular direction rather undergoing equiaxial growth. For instance, hexagonal ZnO and tetragonal rutile usually grow as rod-shaped particles. A loose compact of these nanorods give nanoporous morphology upon heating. Advantage of this method is the tunability of pore size by tuning the aspect ratio of the nanorods. Preparation of porous TiO2, ZnO and hydroxyapatite has been demonstrated from their corresponding nanorods. Chapter-V deals with a solvothermal based technique that has been developed for in-situ deposition of nanoparticles on any plane or curved surfaces conformally. This has been demonstrated for nanoparticles of FeCo, Au, Co, CdS on substrates like glass, mica, Si, NaCl, Al2O3 M-plane and also conformal coating of Au nanoparticles on polystyrene latex spheres. CdSe on rutile nanorods, ZnO nanorods and CNTs are promising hybrid nanostructures for third generation photovoltaics and their successful preparation has been detailed in the chapter. The mechanism proposed is based on dominant attractive sphere-plate interaction under high temperature and high autogeneous pressure condition which at reduced density and surface tension of the solvent reduces the dispersibility of the nanoparticle and allow effective spreading of the nanoparticles on the substrate. This method is also advantageous for coating of complicated geometry like inner walls of porous structures. Chapter-VI presents a method to coat chalcogenide nanoparticles on mesoporous TiO2 without any molecular linker which can enhance the electron injection rate from the chalcogenide quantum dots to TiO2. CdS, PbS can be easily synthesized through aqueous chemistry. For deposition of these sulfides, the ion layer gas absorption and reaction (IGLAR) method was modified to form uniform dense nanoparticles on anatase and ZnO surfaces. Nitrate salts of corresponding metal ions are dried directly on the semiconductor surface and instead of exposing it to H2S gas, it was treated with a concentrated sulfide solution. This introduces two competitive process i) dissolution of nitrate salt ii) formation of the metal sulfide. This dissolution step was absent when treated with H2S gas (IGLAR) and hence lead to a continuous coating. We have successfully produced CdS-TiO2 and PbS-TiO2 composites using this approach. Photoelectrochemical measurements on CdSTiO2 composites show an overall efficiency of 2.8% which is among the highest values obtained for this system demonstrating the applicability of the method to engineer interfaces to achieve high efficiency solar cells. Chapter-VI explores the combination of strategies of nanocrystal conversion chemistry with previously described sol-gel combustion technique to create dense and uniformly coated QD sensitized TiO2 electrode without compromising heat-treatment routines which is essential for better adhesion and to enhance performance with reduced leakage. Intimate biphasic oxide mixtures of PbO and CdO with TiO2 are first synthesized by nonhydrolytic solgel process with is followed by combustion to produce porous morphology. This powder can be coated as electrode and can sustain high temperature heat treatment routines and finally can be selectively converted to sulfides with Na2S treatment as TiO2 is immune to sulfidation under this condition. Materials at different stages are characterised by XRD, TEM, EDS, UV-Vis and XPS.

Open-framework materials constitute an important area of study in materials chemistry, because of their potential applications in areas such as sorption and catalysis. Furthermore, these materials exhibit fascinating architectures with unusual bonding and coordination patterns. Besides aluminosilicate zeolites and metal phosphates, metal carboxylates constitute an important family of open-framework structures. In this thesis, results of investigations of a variety of open-framework metal carboxylates, as well as a new family of rare-earth sulfates are presented. More importantly, studies directed towards an understanding of the mechanism of formation of open-framework phosphates and carboxylates and the importance of synthesis parameters like temperature in determining the dimensionality of the products are discussed at length. After providing an introduction to open-framework compounds (Part 1), the thesis (Part 2) presents the results of the investigations of metal carboxylates employing both transition metal and rare-earth metal ions with various organic linkers, ranging from aromatic squarate dianion, aliphatic dicarboxylates like oxalate, adipate, succinate, aminocarboxylates (which contain both the amine and the carboxylate group in the same moiety) and dihydroxybenzoates. Some of these compounds have large channels, for example, both the lanthanum mixed aliphatic dicarboxylates, strontium dihydroxybenzoate etc. Some even show unusual properties, example, a mixed valent iron (II, III) glycinate has a perfect kagome structure and shows unusual magnetic properties, entirely different from those of ordinary Fe(III) kagome structures, copper derivative of 6-amincaproic acid has large channels and remains crystalline porous even after dehydration, a cobalt oxalato-squarate has both oxalate and squarate moiety in the same structure, where the oxalate is produced in situ by the oxidation of squarate under hydrothermal conditions in the basic medium. While the phosphate and the silicate anions are the most common basic building units in open-framework inorganic structures, the possibility of building open architectures with the sulfate anion as the basic building unit has been explored in Part 3. The results have been rewarding and both layered and three-dimensional rare-earth sulfates with large channels and possessing a α-Po structure or (6, 3) nets with continuous M-O-M connectivity in two dimensions have been obtained. The most intriguing question in the area of open-framework structures relates to the mode of formation. In Part 4, the mechanism of formation of both metal phosphates and metal carboxylates have been discussed. This part includes a study of the transformations of four-membered ring phosphates to higher dimensional structures (like 3D sodalite-related structure), through lower-dimensional structures, involving a progressive building-up mechanism. Similar progressive building-up mechanism has also been studied for metal carboxylates. The importance of synthesis parameters like temperature in governing the dimensionality of the products has been studied.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / In this study, two tungsten-based oxides, iron tungstate (FeWO4) and zinc tungstate (ZnWO4), were synthesized by the routes microwave-assisted hydrothermal and solvo-hidrothermal, respectively. The iron tungstate oxide was used as a catalyst in heterogeneous photo-Fenton reaction for removal of Amaranth dye, whereas the zinc tungstate was used as a support for the immobilization of inulinase by adsorption process. Both materials produced were characterized by techniques such as X-ray diffraction (XRD), nitrogen adsorption-desorption analysis by Brunauer-Emmett-Teller method (BET), Fourier transform infrared spectroscopy (FTIR) and particle size distribution analysis by laser diffraction. For heterogeneous photo-Fenton reaction, an experimental design was used to study the effect of variables such as pH, hydrogen peroxide concentration and dye concentration on the degradation efficiency of Amaranth dye. The inulinase immobilization on the ZnWO4 oxide was investigated in two temperatures. According to the characterization results, both synthesized material has a porous structure and high crystallinity. The FeWO4 oxide showed a satisfactory ability to degrade amaranth dye, and under the optimum reaction conditions, 97% decolorization and 58% mineralization were obtained. Furthermore, the efficiency and stability of this catalyst were maintained high after five cycles of reuse. The ZnWO4 oxide showed a satisfactory inulinase adsorption, where the best result was found to be 605 U.g-1 at 30 oC. / Neste trabalho, dois óxidos a base de tungstênio, tungstato de ferro (FeWO4) e tungstato de zinco (ZnWO4), foram sintetizados pelos métodos hidrotérmico assistido por micro-ondas e solvo-hidrotérmico, respectivamente. O tungstato de ferro foi utilizado como catalisador na reação heterogênea de foto-Fenton para remoção do corante orgânico Amaranto, enquanto que o tungstato de zinco foi utilizado como suporte para imobilização da inulinase pelo processo de adsorção. Ambos os materiais produzidos foram caracterizados pelas técnicas tais como difração de raios-X (DRX), análise de adsorção-dessorção de nitrogênio pelo método de Brunauer-Emmett-Teller (BET), espectroscopia de infravermelho por transformada de Fourier (FTIR) e análise de distribuição do tamanho de partículas por difração laser. Para a reação foto-Fenton heterogênea, um planejamento experimental f oai empregado a fim de estudar os feitos das variáveis pH, concentração de peróxido e de corante sobre a eficiência de degradação do corante amaranto. A imobilização de inulinase sobre o óxido ZnWO4 foi investigada em duas temperaturas. De acordo com os resultados da caracterização, ambos os materiais sintetizados apresentaram uma estrutura porosa e com alta cristalinidade. O óxido FeWO4 demonstrou uma satisfatória habilidade para degradar o amaranto, sendo que nas condições ótimas de reação, 97 % de descoloração e 58% de mineralização foram obtidos. Além disso, a eficiência e estabilidade desse catalisador foram mantidas elevadas após cinco ciclos de reuso. O óxido ZnWO4 apresentou uma satisfatória adsorção de inulinase, onde o melhor resultado encontrado foi de 605 U.g-1 na temperatura de 30 oC.

In this work, the nonaqueous synthesis of binary and ternary metal oxide nanoparticles is investigated for a number of technologically important materials. A strong focus was put on studying the reaction mechanisms leading to particle formation upon solvothermal treatment of the precursors, as an understanding of the formation processes is expected to be crucial for a better control of the systems, offering the potential to tailor particle size and morphology.<br><br> The synthesis of BaTiO3 was achieved by solvothermal reaction of metallic barium and titanium isopropoxide in organic solvents. Phase-pure, highly crystalline particles about 6 nm in size resulted in benzyl alcohol, whereas larger particles could be obtained in ketones such as acetone or acetophenone. In benzyl alcohol, a novel mechanism was found to lead to BaTiO3, involving a C–C coupling step between the isopropoxide ligand and the benzylic carbon of the solvent. The resulting coupling product, 4-phenyl-2-butanol, is found in almost stoichiometric yield. The particle formation in ketones proceeds via a Ti-mediated aldol condensation of the solvent, involving formal elimination of water which induces formation of the oxide. These processes also occurred when reacting solely the titanium alkoxide with ketones or aldehydes, leading to highly crystalline anatase nanoparticles for all tested solvents. In ketones, also the synthesis of nanopowders of lead zirconate titanate (PZT) was achieved, which were initially amorphous but could be crystallized by calcination at moderate temperatures. Additionally, PZT films were prepared by simply casting a suspension of the powder onto Si substrates followed by calcination.<br><br>Solvothermal synthesis however is not restricted to alkoxides as precursors but is also achieved from metal acetylacetonates. The use of benzylamine as solvent proved particularly versatile, making possible the synthesis of nanocrystalline In2O3, Ga2O3, ZnO and iron oxide from the respective acetylacetonates. During the synthesis, the acetylacetonate ligand undergoes a solvolysis under C–C cleavage, resulting in metal-bound enolate ligands which, in analogy to the synthesis in ketones, induce ketimine and aldol condensation reactions.<br><br> In the last section of this work, surface functionalization of anatase nanoparticles is explored. The particles were first capped with various organic ligands via a facile in situ route, which resulted in altered properties such as enhanced dispersibility in various solvents. In a second step, short functional oligopeptide segments were attached to the particles by means of a catechol linker to achieve advanced self-assembly properties. / Die vorliegende Arbeit befasst sich mit der nichtwässrigen Synthese binärer und ternärer Metalloxid-Nanopartikel durch solvothermale Behandlung von Metalloxid-Vorstufen in organischen Lösungsmitteln. Dabei wurde besonderes Augenmerk auf die Reaktionsmechanismen gelegt, da eine genaue Kenntnis des Bildungsmechanismus eine bessere Kontrolle über das Partikelwachstum erwarten lässt, woraus sich die Möglichkeit der genauen Steuerung von Partikelgröße und –form ableitet.<br><br> Bariumtitanat (BaTiO3) konnte durch solvothermale Reaktion von metallischem Barium und Titanisopropoxid in organischen Lösungsmitteln hergestellt werden. Hochkristalline, phasenreine Partikel von etwa 6 nm Durchmesser wurden in Benzylalkohol erhalten, während in Ketonen wie Aceton oder Acetophenon größere Partikel entstanden. In Benzylalkohol läuft ein neuartiger Reaktionsmechanismus ab, der eine C–C-Kupplungsreaktion zwischen dem Isopropoxid und dem benzylischen Kohlenstoffatom des Lösungsmittels umfasst. Das Kupplungsprodukt 4-Phenyl-2-butanol wird in praktisch stöchiometrischer Ausbeute erhalten. In Ketonen verläuft die Partikelbildung über eine titankatalysierte Aldolkondensation des Lösungsmittels, die formell die Eliminierung von Wasser einschließt, was zur Bildung des Oxids führt. Diese Prozesse liefen auch bei Umsetzung von reinem Titanisopropoxid in Ketonen oder Aldehyden ab, wobei hier hochkristalline Anatas-Nanopartikel entstanden. Auch die Synthese von Bleizirkonat-titanat-Nanopulvern war in Ketonen möglich; die zunächst amorphen Pulver konnten durch Kalzinierung bei relativ geringen Temperaturen in kristalline Nanopartikel überführt werden. Zusätzlich wurden Filme durch Auftragen einer Suspension der Pulver auf Siliziumwafer und anschließende Kalzinierung hergestellt.<br><br>Die solvothermale Synthese kann allerdings auch ausgehend von Metallacetylacetonaten durchgeführt werden. Benzylamin erwies sich hier als ein sehr vielseitiges Lösungsmittel und ermöglichte die Synthese von nanokristallinem In2O3, Ga2O3, ZnO und Eisenoxid ausgehend von den jeweiligen Acetylacetonaten. Im Verlauf der Synthese wird der Acetylacetonatligand unter C–C-Bindungsspaltung solvolysiert. Die entstehenden Enolatliganden reagieren dann unter Ketimin- und Aldolkondensation analog der Solvothermalsynthese in Ketonen weiter.<br><br> Der letzte Teil dieser Arbeit beschäftigt sich mit der Funktionalisierung der Partikel. Zunächst wurden TiO2-Partikel durch verschiedene organische Liganden „in situ“ funktionalisiert, wodurch Eigenschaften wie etwa die Dispergierbarkeit in unterschiedlichen Lösungsmitteln beeinflusst werden konnten. In einem zweiten Schritt wurden kurze Oligopeptidketten über eine Katecholbrücke an die Partikel geknüpft, um anspruchsvolle Selbstanordnungseigenschaften zu erzielen.

In this dissertation, BaTiO3 nanocrystals, Bi4Ti3O12 nanostructured microspheres, and cosubstituted Bi4Ti3O12 nanoparticles and ceramics were prepared using solvothermal, hydrothermal and citrate-gel methods. The ferroelectric properties of the prepared cosubstituted Bi4Ti3O12 ceramics were studied using P–E hysteresis loop, leakage, and polarization fatigue measurements. A two-phase solvothermal synthesis approach for the preparation of hydrophobic BaTiO3 nanocrystals was developed. The two-phase method is based on the growth of nanocrystals at the oil/water interface by the reaction between metal surfactant complexes in the oil phase and a mineralizer in the water phase. Three kind of organic solvents, hexadecene, toluene, and heptane were used as the oil phase and compared to each other with respect to the product quality. The BaTiO3 particles are crystalline with a mean size of 3.7 nm and can be dispersed in a variety of organic solvents forming highly transparent dispersions. A hydrothermal method was developed for the synthesis of Bi4Ti3O12 nanostructured microspheres consisting of granular nanoparticles and nano-platelets. The precursor powder was prepared using a diethylene glycol mediated coprecipitation method. Tailoring of the morphology was achieved by changing the precursor quantity, sodium hydroxide concentration, and reaction time. The formation mechanism of the nanostructured microspheres probably involves aggregation, followed by dissolution and recrystallization. Bi3.25Pr0.75Ti2.97V0.03O12 (BPTV) and Bi3.25La0.75Ti3-xMxO12, (BLTMx, M = Mo, W, Nb, V, x = 0.0–0.12) ferroelectric nanoparticles and ceramics were synthesized using a modified citrate-gel method that has a crystallization temperature as low as 450 °C. The synthesized nanoparticles were spherical ranging from 30 to 100 nm. Except Nb5+, other donor cations were introduced using the corresponding oxides that have advantages in terms of high purity, low cost, and availability. The Bi3.25Pr0.75Ti2.97V0.03O12 ceramic is orthorhombic and its 2Pr and 2Ec values measured at 300 kV/cm were 35 μC/cm2 and 148 kV/cm respectively. The texture, microstructure, and ferroelectric properties of the prepared Bi3.25La0.75Ti3-xMxO12, (BLTMx, M = Mo, W, Nb, V, x = 0.0–0.12) ceramics depend on x. The maximum 2Pr (30–32 μC cm−2) was achieved at an optimum cosubstitution level (x = 0.025 for M6+, x = 0.03 for M5+). The high remanent polarization, low leakage current, and low polarization fatigue render the prepared ceramics promising for practical applications.

Il s'agissait dans ce travail de préparer différentes variétés cristallines d'hydroxyfluorures d'aluminium présentant des tailles nanométrique en vue d'application en catalyse. Pour ce faire une méthode solvothermale assistée par chauffage micro-ondes a été utilisée. La variation des paramètres de synthèse telle que la nature du précurseur cationique, le taux HF/Al ou encore l'utilisation de solvants organiques a permis la préparation de diverses formes cristallines présentant une pureté phasique et un aspect divisé. Trois matériaux ont ainsi été obtenus avec des structures dérivés du pyrochlore (Fd-3m), des bronzes de tungstène hexagonaux (Cmcm) et de type ReO3 (Pm-3m). L'utilisation de nombreuses techniques de caractérisations (DRX, RMN à l'état solide des noyaux 27Al, 19F et 1H, microscopie électronique, mesure de surface spécifique et spectroscopie infra-rouge) ont permis une analyse détaillée des solides préparés. L'impact structural des groupements OH sur la forme cristalline stabilisée a été mise en avant dans le cas du pyrochlore AlF1.7(OH)1.3 et de la forme HTB AlF2.6(OH)0.4. Dans le troisième composé, la stabilisation de molécule d'eau comme ligand a permis l'obtention du premier composé lacunaire dans la famille des fluorures d'aluminium. Ce dernier présente la formule générale suivante Al0.82-0.18F2.46(H2O)0.54. Le traitement d'un gel d'alkoxyfluorures d'aluminium par micro-ondes puis sous fluor gazeux a permis d'obtenir un matériau possédant une très grande surface spécifique (330 m2.g-1). L'étude des propriétés acides de ces matériaux par adsorption de molécules sondes détectées par FTIR a révélé une large gamme d'acidité de Lewis et de Brønsted. Finalement, l'influence de la surface spécifique sur le nombre de sites de Lewis forts a été mise en avant.

In this dissertation, BaTiO3 nanocrystals, Bi4Ti3O12 nanostructured microspheres, and cosubstituted Bi4Ti3O12 nanoparticles and ceramics were prepared using solvothermal, hydrothermal and citrate-gel methods. The ferroelectric properties of the prepared cosubstituted Bi4Ti3O12 ceramics were studied using P–E hysteresis loop, leakage, and polarization fatigue measurements. A two-phase solvothermal synthesis approach for the preparation of hydrophobic BaTiO3 nanocrystals was developed. The two-phase method is based on the growth of nanocrystals at the oil/water interface by the reaction between metal surfactant complexes in the oil phase and a mineralizer in the water phase. Three kind of organic solvents, hexadecene, toluene, and heptane were used as the oil phase and compared to each other with respect to the product quality. The BaTiO3 particles are crystalline with a mean size of 3.7 nm and can be dispersed in a variety of organic solvents forming highly transparent dispersions. A hydrothermal method was developed for the synthesis of Bi4Ti3O12 nanostructured microspheres consisting of granular nanoparticles and nano-platelets. The precursor powder was prepared using a diethylene glycol mediated coprecipitation method. Tailoring of the morphology was achieved by changing the precursor quantity, sodium hydroxide concentration, and reaction time. The formation mechanism of the nanostructured microspheres probably involves aggregation, followed by dissolution and recrystallization. Bi3.25Pr0.75Ti2.97V0.03O12 (BPTV) and Bi3.25La0.75Ti3-xMxO12, (BLTMx, M = Mo, W, Nb, V, x = 0.0–0.12) ferroelectric nanoparticles and ceramics were synthesized using a modified citrate-gel method that has a crystallization temperature as low as 450 °C. The synthesized nanoparticles were spherical ranging from 30 to 100 nm. Except Nb5+, other donor cations were introduced using the corresponding oxides that have advantages in terms of high purity, low cost, and availability. The Bi3.25Pr0.75Ti2.97V0.03O12 ceramic is orthorhombic and its 2Pr and 2Ec values measured at 300 kV/cm were 35 μC/cm2 and 148 kV/cm respectively. The texture, microstructure, and ferroelectric properties of the prepared Bi3.25La0.75Ti3-xMxO12, (BLTMx, M = Mo, W, Nb, V, x = 0.0–0.12) ceramics depend on x. The maximum 2Pr (30–32 μC cm−2) was achieved at an optimum cosubstitution level (x = 0.025 for M6+, x = 0.03 for M5+). The high remanent polarization, low leakage current, and low polarization fatigue render the prepared ceramics promising for practical applications.

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