Made available in DSpace on 2017-07-24T19:37:51Z (GMT). No. of bitstreams: 1 FILIPY GOBBO MARANHA.pdf: 9851760 bytes, checksum: 4b667c83e658c04d1de2cc4091b59e0c (MD5) Previous issue date: 2014-07-30 / Fundação Araucária de Apoio ao Desenvolvimento Científico e Tecnológico do Paraná / The system LaAl1-xFexO3 was synthesized through the Modid Pechini Method (MPM) and solid state reaction (SSR) to evaluate its applicability as a ceramic pigment. The MPM synthesis was carried out with metallic ion nitrates and thermal treatment at 910 °C for 4 hours, while the SSR syntheses comprised metallic ion oxides and thermal treatment at 1400 °C for 4 hours. The pigments obtained through MPM were characterized through X-ray diraction, structural renement through the Rietveld method, Mossbauer spectroscopy, eld eect scanning electronic microscopy, UV-Vis diuse re ectance and analysis of colorimetric values through the CIEL*a*b*. The SSR obtained pigments were not submitted to Mossbauer spectroscopy and the Rietveld Method structural renement analyses. MPM synthesized pigments were obtained with perovskite as the only phase, crystallizing in the rhombohedric crystalline system with values 0:00 x 0:80, and values x > 0:80 in the orthorhombic system. The SSR revealed the possible presence of secondary phases in the formation of the pigment crystalline structure and the values x 0:60 crystallized in the rhombohedric system, and values x > 0:60 in the orthorhombic system. The pigments obtained presented color between green and orange/red. Their use in ceramic pieces was also evaluated. / O sistema LaAl1 FexO3 foi sintetizado pelo método Pechini modificado (MPM) e por realização do estado sólido (RES) para avaliar a sua aplicabilidade como pigmento cerâmico. A síntese pelo MPM foi realizada com os nitratos dos íons metálicos e posterior tratamento térmico de 910 °C por 4 h enquanto que, para a síntese por RES foi utilizado os óxidos dos íons metálicos e tratamento térmico de 1400 °C por 4 h. Os pigmentos obtidos pelo MPM foram caracterizados pelas técnicas de difração de raios X, de renamento estrutural pelo método de Rietveld, de espectroscopia Mossbauer, de microscopia eletr^onica de varredura por efeito de campo, de re ect^ancia difusa na regi~ao do UV-Visível e de análise dos valores colorimetricos pelo método CIEL*a*b*. Nos pigmentos obtidos por RES não foram realizadas analises de espectroscopia Mossbauer e de refinamento estrutural pelo método de Rietveld. Pigmentos sintetizados pelo MPM foram obtidos com a formação da perovskita como unica fase, cristalizando-se no sistema cristalino romboedrico com valores de 0; 00 x 0; 80, e no ortorrômbico para valores de x > 0; 80. Pela RES, foi observado a possível presenca de fases secundárias na formação das estruturas cristalinas dos pigmentos sendo que, valores de x 0; 60 cristalizaram-se no sistema romboedrico, e valores de x > 0; 60 no sistema ortorrômbico. Os pigmentos obtidos apresentaram colorações entre verde e laranja/vermelho. A aplicação dos mesmos em peças cerâmicas também foi avaliada.

The calcium phosphates have been extensively studied for biomedical applications due to their chemical and structural similarities with our mineral phase of teeth and bones. In this work, biphasic calcium phosphate ceramics - BCP (mixture of hydroxyapatite and β-tricalcium phosphate, Hap/β-TCP) pure and doped with magnesium were obtained by solid state reaction. Magnesium (Mg) is known as an important element in the composition of bones and teeth. Recent research has shown that the addition of Mg in BCP structure improves consists mainly in bone metabolism and mechanical properties, without affecting its biocompatibility. The samples were prepared by solid-state reaction, using calcium carbonate, monobasic ammonium phosphate and magnesium nitratehexahydrate, as precursorssource of calcium, phosphate and magnesium, respectively. For pure BCP samples,it was investigated the influence of heat treatment on the formation of the material and for samples doped with magnesium,it investigated the different doping levels in the BCP structure. Several characterization techniques were used. The composition of the crystalline phase and morphology of the prepared materials were characterized by X-ray Diffraction and Electron Scanning Microscopy, respectively. The functional groups were analyzed using Fourier Transform Infrared Spectroscopy and Raman Spectroscopy. Cytotoxicity tests were carried out and the results suggested that the materials prepared in this work have for biological application as biomaterials. / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Os Fosfatos de cálcio têm sido amplamente estudados para aplicações biomédicas devido à sua similaridade química e estrutural com a fase mineral dos nossos ossos e dentes. Neste trabalho, cerâmicas bifásicas de fosfato de cálcio - BCP (mistura de hidroxiapatita e β-fosfato tricálcico, Hap/β-TCP) purase dopadascom magnésio foram obtidas através da síntese de reação de estado sólido. O magnésio (Mg) é conhecido como um importante elemento na composição dos ossos e dentes. Recentes pesquisas tem mostrado que a adição de Mg na estrutura BCP melhora o composto, principalmente, no metabolismo ósseo e nas propriedades mecânicas, sem afetar a sua biocompatibilidade. As amostras foram preparadas através da síntese reação de estado sólido, usando carbonato de cálcio, fosfato de amônio monobásico e nitrato de magnésio hexahidratado, como fonte precursora de cálcio, fosfato e magnésio, respectivamente. Para as amostras de BCP puras, foi investigada a influência do tratamento térmico na formação do material e para as amostras dopadas com magnésio, investigamos os diferentes teores de dopantes na estrutura do BCP. Diferentes técnicas de caracterizações foram utilizadas. A composição da fase cristalina e a morfologia dos materiais preparados foram caracterizadas por Difração de Raios-X e Microscopia Eletrônica de Varredura, respectivamente. Os grupos funcionais foram analisados usando Espectroscopia de infravermelho por Transformada de Fourier e Espectroscopia Raman. Testes de Citotoxicidade foram realizados e os resultados sugerem que os materiais preparados neste trabalho, apresentam potenciais como biomaterial em aplicações biológicas.

Made available in DSpace on 2015-05-14T13:21:14Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 5622993 bytes, checksum: 5f55f5275c3e644a55c5f60e02cff6ad (MD5) Previous issue date: 2012-05-05 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Ferrites are well studied materials due to their wide application as: gas detector, optical, electronic and magnetic devices, catalyst and pigments. In the synthesis of materials, the properties are extremely influenced by the synthesis method. In this work, four methods were used in the synthesis of spinel ferrites with composition Zn1-xCuxFe2O4 (x = 0,0; 0,25; 0,50; 0,75; 1,0). These were: microwave assisted hydrothermal method (HMO), polymeric precursor (PP), solid state reaction (ES) and thermal decomposition (CA). The samples were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), Raman spectroscopy, ultraviolet and visible spectroscopy (UV-Vis), surface area analysis by the BET method e field emission scanning electronic microscopy (FE-SEM). The synthesis realized with different methods presented very distinct results according to the characterization methods. The sample with composition Zn0,75Cu0,25Fe2O4 was selected as standard for comparison among the applied methods. Samples obtained by the hydrothermal method presented high surface area (128 m2.g-1) and using the particle size obtained by BET and crystallite size calculated from the XRD patterns, it was estimated that there is about 1 crystallite per particle. All samples had high short- and long-range disorder. The sample synthesized by de PP method presented the highest crystallinity, with high short and long range order, leading to a high photoconductivity, intermediary surface area due to the sintering among small particles. The CA method presented an intermediate characteristic between the PP and ES methods. Comparing to HMO method, the PP, ES and CA ones presented small surface areas (not exceeding 2 m2.g-1), and about 9 times more crystallites per particle. Generally, the formation of ZnFe2O4 spinel was achieved by all methods applied, with the synthesis of CuFe2O4 was not possible depending on the reaction media or at lower temperatures. / As ferritas são materiais bastante estudados devido às diversas aplicações como: detector de gases, dispositivos ópticos, eletrônicos e magnéticos, catalisadores e pigmentos. Na síntese de materiais, essas propriedades são influenciadas pelo método de síntese. Neste trabalho, quatro métodos foram empregados na síntese das ferritas do tipo espinélio com composição Zn1-xCuxFe2O4 (x = 0,0; 0,25; 0,50; 0,75; 1,0). Estes foram: o hidrotermal assistido por micro-ondas (HMO), o precursor polimérico (PP), reação no estado sólido (ES) e decomposição térmica (CA). As amostras foram caracterizadas por difração de raios-X (DRX), espectroscopia na região do infravermelho (IV), espectroscopia Raman, espectroscopia na região do ultravioleta e do visível (UV-Vis), análise de área superficial pelo método de BET e microscopia eletrônica de varredura com emissão de campo (MEV-EC). Nas sínteses realizadas pelas diferentes metodologias, resultados diferentes foram obtidos em todas as técnicas empregadas. A amostra de composição Zn0,75Cu0,25Fe2O4 foi utilizada como composição padrão como comparação entre os métodos. Amostras obtidas pelo método hidrotermal apresentaram elevada área superficial (128 m2.g-1) e utilizando o tamanho de partícula calculado pelo BET e o tamanho de cristalito calculado pela difração, pode ser estimado que praticamente há cerca de 1 cristalito por partícula. Todas as amostras apresentaram elevada desordem a curto e a longo alcance. A amostra sintetizada pelo método PP apresentou a maior cristalinidade, com elevada ordem a curto e longo alcance, gerando alta fotocondutividade, com área superficial intermediária, devido à sinterização entre partículas pequenas. O método CA, em geral, apresentou comportamento intermediário entre o método PP e ES. Os métodos PP, ES e CA, quando comparados ao método HMO, apresentaram pequena área superficial (não excedendo 2 m2.g-1) e cerca de 9 vezes mais cristalitos por partícula. De um modo geral, a formação do espinélio ZnFe2O4 foi alcançada por todos os métodos utilizados, enquanto a síntese do CuFe2O4 não foi possível em alguns meios reacionais ou em temperaturas mais baixas.

O galato de lantânio contendo substituições parciais de estrôncio e magnésio (La1-xSrxGa1-yMgyO3-δ) apresenta estrutura tipo perovsquita e alta condutividade para íons de oxigênio. Outras características desta cerâmica são o extenso domínio eletrolítico e a baixa condutividade eletrônica. É um material promissor para uso como eletrólito sólido em células a combustível de óxido sólido que operam em temperaturas intermediárias, devido sua alta condutividade iônica e estabilidade em uma ampla faixa de pressão parcial de oxigênio. Neste trabalho, a composição La0,9Sr0,1Ga0,8Mg0,2O3-δ foi preparada pelo método convencional de mistura de óxidos a partir de diferentes rotas e pelo método de complexação de cátions. As amostras foram consolidadas pelo método convencional de sinterização e por sinterização rápida. Pelo método de mistura de óxidos foi possível obter a fase ortorrômbica do LSGM, mas não foi possível eliminar as fases SrLaGaO4, La4Ga2O9 e SrLaGa3O7, independente das condições de sinterização utilizadas. Precipitados de óxido de magnésio foram observados nas amostras preparadas pelos dois métodos de síntese empregados identificados apenas por microscopia eletrônica de varredura. As densidades obtidas foram superiores a 97% da densidade teórica em amostras sinterizadas a 1450 °C/4 h, para os materiais preparados por mistura de óxidos. Amostras preparadas por método de complexação de cátions e aquelas consolidadas por sinterização rápida apresentaram menores valores de densidade. Grãos de tamanhos micrométricos foram obtidos para os dois métodos de sinterização. Amostras calcinadas a 1250°C apresentaram maiores densidades e maiores valores de condutividade iônica dos grãos e dos contornos de grãos, quando comparadas com as demais amostras. / Lanthanum gallate with partial substitution on La and Ga sites (La1-xSrxGa1-yMgyO3-δ) has perovskite structure and high oxide-ion conductivity. Other properties of this ceramic material comprise a relatively wide electrolytic domain and low electron conductivity. Doped lanthanum gallate is a potential solid electrolyte for intermediate-temperature solid oxide fuel cells due to its high ionic conductivity and stability in a wide range of oxygen partial pressure. In this work, the composition La0.9Sr0.1Ga0.8Mg0.2O3-δ was prepared by the conventional method of mixing of the starting oxides followed by different processing routes and by the cation complexation method. The ceramic specimens were consolidated by conventional sintering and by fast firing. All specimens prepared by solid state reaction show the characteristic orthorhombic phase of lanthanum gallate and SrLaGaO4, La4Ga2O9 and SrLaGa3O7 secondary phases, independent on the method of sintering. Energy dispersive X-ray spectroscopy coupled to scanning electron microscopy evidenced that all prepared specimens contain MgO grains precipitated along the grain boundaries. High relative densities were obtained for specimens prepared by solid state reaction and consolidated by conventional sintering at 1450 °C/4 h. All specimens exhibit micron sized grains independent on the sintering method. The highest values of relative density and ionic conductivity were obtained for specimens calcined at 1250°C.

The main objective of this thesis is to evaluate the effect of production technology on the properties of forsterite. The theoretical part contains the fundamental parameters and the use of forsterite in the industry together with various possibilities of forsterite production. The main emphasis is placed on the characteristics of the raw materials for production as well as the raw materials possibilities of the Czech Republic. The end of the theoretical part contains a design for the production technology of forsterite, which will be verified in the practical part. The practical part verifies the use of various raw materials for the composition of the raw material mixture. The created test specimens were subjected to the X-ray diffraction analysis, the determination of tensile bending strength, thermal conductivity coefficient, apparent porosity, bulk density, apparent density, water absorption, permanent change in dimension on heating, refractoriness, thermal expansion coefficient, refractoriness under load and the thermal shock resistance. At the end of the practical part is the verification of the design of the production technology of forsterite.

The Master´s thesis deals with the preparation of perovskite oxides by glycine synthesis with following characterization and analysis of catalytic activity. Especially is discussed crystallographic structure. In the theoretical part were first summarized the available information of the properties and usage of perovskite oxides. In the experimental part of the work was carried out the preparation of perovskite oxides and were made chemical analysis. Moreover a catalytic activity of selected perovskites has been studied and have been illustrated their crystal structure.

<p>Predmet istraživanja ove doktorske disertacije&nbsp;su prahovi litijum-indijum oksida dopirani&nbsp;različitim jonima retkih zemalja (Eu³⁺; Sm³⁺;&nbsp;Er³⁺; Yb³⁺), sintetisani reakcijom u &nbsp;čvrstoj fazi.&nbsp;Litijum-indijum oksid ima raznovrsne&nbsp;potencijalne primene u viduscintilatora, &nbsp;matrice&nbsp;fosfora za jone retkih zemalja, za&nbsp; čuvanje i&nbsp;konverziju energije i u fotokatalizi. U&nbsp;<br />istraživanju je ustanovljena optimalna metoda&nbsp;sinteze fazno&nbsp; čistih prahova novih fosfora&nbsp;<br />LiInO₂:RE^3+&nbsp;i izvr&scaron;ena njihova detaljna&nbsp;karakterizacija primenom difrakcije X-zraka,&nbsp;<br />skenirajuće elektronske mikroskopije,&nbsp;termogravimetrije i diferencijalno termijske&nbsp;analize, Ramanske spektroskopije i difuzno-refleksione spektroskopije. &nbsp;Fotoluminescentna&nbsp;spektroskopija je primenjena u cilju ispitivanja&nbsp;osobina presudnih za &nbsp;primenu ovih materijala.&nbsp;Emisioni spektri i vrednosti vremena života&nbsp;pokazuju efikasne potencijalne fosfore, dok&nbsp;ispitivanja emisije uzorka LiInO₂:Er^3+&nbsp;na&nbsp;različitim temperaturama ukazuju na to da je u&nbsp;pitanju veoma dobar temperaturni senzor u&nbsp;<br />oblasti temperatura (10-300) K.</p> / <p>The subject of this dissertation are powders of&nbsp;lithium-indium oxide doped with different rare&nbsp;earth ions (Eu³⁺; Sm³⁺; Er³⁺; Yb³⁺), synthesized&nbsp;by solid-state reaction. Lithium-indium oxide&nbsp;has a variety of potential applications in the&nbsp;form of scintillators, phosphor matrixes for rare-earth ions, storage and energy conversion&nbsp;devices and photocatalysts. In this study the&nbsp;optimal method of synthesis of pure-phased&nbsp;powders of new phosphors LiInO₂:RE^3+&nbsp;was&nbsp;determined. Also, their detailed characterization&nbsp;<br />using the X-ray diffraction, scanning electron&nbsp;microscopy, thermogravimetry and &nbsp;differential&nbsp;thermal analysis, Raman spectroscopy and&nbsp;diffuse-reflection spectroscopy &nbsp;was performed.&nbsp;Photoluminescence spectroscopy was applied to&nbsp;investigate the properties crucial for the&nbsp;application of these materials. Emission spectra&nbsp;and lifetime values, showed these materials are&nbsp;potential efficient phosphors. Examining the&nbsp;emission of LiInO₂:Er^3+&nbsp;sample at different&nbsp;temperatures indicated that this is a very good&nbsp;temperature sensor in the temperature range (10-300) K.</p>

We are living in an age where the demand for energy is growing rapidly. This means that supplies to easily accessible oil and natural gas is unlikely to keep up with the demand as times goes on. The world will have to use energy more efficiently and increase its use of other sources of energy. This study is aiming at developing materials that will improve the power conversion efficiency of photovoltaic cells by using up and down-converting phosphor materials. ZnTiO3-Zn2TiO4 composite and ZnTiO3 phosphors doped with Er3+,Yb3+, Eu3+ and Al3+, which display up and down-converted luminescence were synthesized by a simple high temperature conventional solid state reaction method. The structure, particle morphology, absorption, photoluminescent properties and elemental distribution were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-Vis-NIR absorption spectrometer, photoluminescence (PL) spectroscopy and time of flight secondary ion mass spectroscopy (TOF-SIMS), respectively. ZnTiO3-Zn2TiO4 composite doped with different concentration of Er3+ ions was synthesized via solid state chemical reaction method at 1100 ℃. The X-ray diffraction (XRD) confirmed the crystallization of both the hexagonal ZnTiO3 and cubic spinel Zn2TiO4 phases of the composite. The SEM images of ZnTiO3-Zn2TiO4:Er3+ composite showed that the particle morphology was made up of faceted hexagons. Furthermore, the ZnTiO3-Zn2TiO4:Er3+ phosphors were excited in the near-infrared (NIR) region using a laser diode with a wavelength of 980 nm and displayed both green and red up-conversion emission bands in the visible range at 543, 553, 650 – 670 nm. These emission bands correspond to 2H11/2, 4S1/2→ 4 I15/2 and 4F9/2→ 4 I15/2 transitions of Er3+ ions. However, the interaction mechanisms involved in the upconversion process of ZnTiO3-Zn2TiO4:Er3+ phosphor is discussed with the help of an energylevel schematic diagram and the number of the photons involved in the up-conversion luminescence process were of a double photon mechanism. The decay lifetimes were studied by fitting the luminescence decay curve with a single-component exponential decay. Er3+ and Yb3+ incorporated zinc titanate (ZnTiO3) phosphor powders were synthesized using conventional solid-state reaction method at 800 ℃. A ZnTiO3:Er3+,Yb3+ phosphor that resembled an ecandrewsite single phase with space group R-3 (148) was obtained, as proven by X-ray diffraction (XRD). The SEM image showed a surface morphology composed of agglomerated irregular shaped particles. The energy band gap of ZnTiO3 was engineered by incorporating different concentration of the dopant ions. After irradiating ZnTiO3:Er3+with a 980 nm laser beam, the phosphor up-converted the photon energy to display green and red emissions in the visible range that were positioned at 527, 545 and 665 nm. Enhancement of the luminescence intensity of ZnTiO3:Er3+ phosphor was achieved by variation of Er3+ concentration. Co-doping with Yb3+ ions proved to be effective in enhancing the luminescence intensity of the optimized Er3+ ion emission and new emission bands at 410 and 480 nm, through an energy transfer mechanism were observed. The enhancement of the lifetime of the up-conversion luminescence was also achieved by co-doping ZnTiO3:Er3+ phosphor with Yb3+ ion. The energy transfer mechanisms involved in Er3+ - Yb3+ co-doped ZnTiO3 phosphor was illustrated and discussed in detail. The ZnTiO3:Er3+, Yb3+ thin films were successfully deposited by pulsed laser deposition (PLD) by varying the silicon (100) substrate temperature. The distribution of the ions in the films was investigated and the TOF-SIMS showed that the ions were homogeneously distributed throughout the ZnTiO3 host lattice which indicated a successful incorporation of the Er3+ and Yb3+ ions. The optical response of the phosphors revealed that the reflectance percentages of the ZnTiO3:Er3+, Yb3+ vary with the silicon substrate temperature due to the differences in the thickness and morphological roughness of the thin films. The ZnTiO3:Er3+, Yb3+ thin films also exhibited up-conversion emission from Er3+ electronic transitions, with violet, blue, green and red emission lines at 410, 480, 525, 545 and 660 nm from 2H9/2 → 4 I15/2, 4F7/2 → 4 I15/2, 2H11/2 → 4 I15/2, 4S3/2 → 4 I15/2 and 4F9/2 → 4 I15/2 transitions, respectively. These up-conversion emissions were enhanced by increasing the silicon substrate temperature during the deposition. ZnTiO3 host co-doped with Eu3+ and Al3+ was synthesized by solid state reaction to convert the UV photons to visible photons. Charge compensation effects of Al3+ incorporated ZnTiO3:Eu3+ as a co-dopant ion was reported in detail. The structural and morphological characterization show that the addition of Eu3+ and Al3+ does not affect the phase formation and the surface morphology of the host. The visible emission intensity of Eu3+ ions for an optimal concentration of 2 mol% under 395 nm excitation, was enhanced by incorporating Al3+. The energy level diagram showing the charge compensation mechanism was proposed for the co-doped system. / College of Engineering, Science and Technology

Les objectifs de cette thèse peuvent être scindés en trois. Le premier consiste à choisir un matériau conducteur en ions en vue de son utilisation comme électrolyte au sein dune pile à combustible à oxyde solide. Ce matériau doit être stable dans une atmosphère aussi bien réductrice quoxydante ; compatible avec les autres composants de la pile (cathode, anode et interconnecteur) tant dans le domaine chimique (interactions limitées entre les composants) que physique (coefficient de dilatation thermique proche de ceux des autres composants) ; et finalement, présenter une conductivité en ions suffisante au bon fonctionnement de la pile dans le domaine des température considéré (entre 500°C 800°C). La réponse à cet objectif est détaillée dans les deux premiers chapitres. Comme plusieurs matériaux soffraient potentiellement à nous, nous avons choisi détudier un type de solution solide dérivé du gallate de lanthane. Lors de lélaboration de pièces céramiques, le choix de la granulométrie des poudres de départ ainsi que leur mise en forme sont sans nul doute les étapes qui revêtent le plus dattention : elles sont responsables des défauts structuraux et/ou microstructuraux des pièces à cru. Par conséquent, une mauvaise homogénéité chimique ou une distribution en taille de particules inadaptée, mais également, des conditions de mise en forme trop douces ou trop sévères confèreront aux pièces produites des propriétés déplorables quil sera probablement difficile daméliorer par la suite. Afin de minimiser la nature et le nombre de ces défauts, une compréhension plus détaillée du « chemin réactionnel » présente donc un intérêt tout particulier. Cette compréhension peut être réalisée en étudiant les mécanismes structuraux et microstructuraux survenant tout au long du cycle de production des pièces. Ainsi, le deuxième objectif établi, plus expérimental, porte sur lélaboration dune poudre de La0,9Sr0,1Ga0,8Mg0,2O2,85 chimiquement homogène et de distribution en taille de particules adaptée à la mise en forme par compaction (Chapitre III à VI). Dans ces chapitres, nous étudierons linfluence du procédé de synthèse sur les mécanismes structuraux et microstructuraux. Cette poudre sera ensuite employée pour préparer une pastille à cru qui servira à obtenir, après un traitement thermiquement, une pièce céramique dense (les mécanismes du frittage seront étudiés au Chapitre VII). Pour terminer, la troisième partie de ce travail repose sur la compréhension des corrélations « structure propriétés » et « microstructure propriétés » ; plus particulièrement sur les propriétés de conduction des anions O2- qui seront étudiées à laide de la spectroscopie dimpédance complexe sur plusieurs échantillons frittés (Chapitre VIII). Par conséquent, ce travail peut être résumé de la manière suivante. Le premier chapitre décrit sommairement les différents types de piles à combustible et, plus particulièrement, la pile à combustible à oxyde solide. Il discute ces avantages et inconvénients et détaille quelques mécanismes de conduction présents aux électrodes et dans lélectrolyte. Finalement, il explique les raisons pour lesquelles le gallate de lanthane substitué au strontium et au magnésium (La1-xSrxGa1-yMgyO3-) a été choisi comme matériau détude. Le deuxième chapitre explique les raisons pour lesquelles la composition La0,9Sr0,1Ga0,8Mg0,2O2,85 a été retenue. Il décrit également les mécanismes de conduction à léchelle atomique et montre la corrélation existant entre la structure cristallographique et les propriétés électriques. Finalement, il présente les propriétés microstructurales essentielles que doit posséder un électrolyte pour le bon fonctionnement dune pile à combustible et fixe ainsi les objectifs expérimentaux de ce travail. Les quatre chapitres suivants décrivent les procédés de synthèse employés. Ils expliquent comment le composé multi-cationique La0,9Sr0,1Ga0,8Mg0,2O2,85 se forme à léchelle atomique et montrent également linfluence du procédé de synthèse sur la granulométrie des poudres obtenues. Ainsi, le chapitre III décrit la réaction à létat solide. Il montre que les phases secondaires ne peuvent être évitées, que seule une granulométrie relativement grossière est obtenue et que les étapes de broyage restent nécessaires. Pour éviter ces inconvénients, nous avons exploré quelques procédés de synthèse dits de chimie douce. Dans ce cas, lhomogénéisation des réactifs réalisée à léchelle moléculaire permet de limiter, ou au moins, de mieux contrôler la formation des phases secondaires. De plus, les propriétés des poudres obtenues (distribution en taille de particules, morphologie) dépendent alors essentiellement de lagent texturant employé dans le procédé de synthèse. Le chapitre IV décrit la méthode Pechini où le composé est préparé à partir dacide citrique et déthylène glycol. Le chapitre V décrit un procédé de prise au piège stérique qui utilise lalcool polyvinylique et, finalement, le chapitre VI décrit un procédé de synthèse innovant qui utilise lhydroxypropylméthylcellulose comme agent texturant et qui permet de préparer le précurseur du La0,9Sr0,1Ga0,8Mg0,2O2,85 en trois étapes (Gélification Lyophilisation Autocombustion). Le chapitre VII débute par la description des mécanismes de densification en phase solide. Il présente ensuite les caractéristiques de chacune des poudres retenues et décrit leur mise en forme. Les comprimés à cru sont caractérisés et traités thermiquement en suivant leur évolution microstructurale jusquau matériau fritté. Pour terminer, le chapitre VIII introduit la spectroscopie dimpédance appliquée à létude des matériaux conducteurs ioniques. Il présente la corrélation « microstructure circuits équivalents » ainsi que les limitations instrumentales. Les propriétés électriques des comprimés frittés sont étudiées et le matériau est considéré selon son caractère résistif ou selon ses temps de relaxation diélectrique. Finalement, les énergies dactivation des mécanismes de conduction sont déterminées. Le lecteur notera que tout au long de cette thèse, nous nous sommes plutôt intéressés aux aspects fondamentaux de létude quà la résolution de problèmes de nature technologique.

Structures semi-conductrices à base de NiTiO3, et l'étude de leurs propriétés dans le but de les appliquer en photocatalyse. Une étude théorique et des simulations numériques ont été effectuées pour analyser les propriétés électroniques, vibrationnelles et optiques de NiTiO3 massif ou sous forme de clusters nanométriques. Les poudres NiTiO3 ont été synthétisées par sol-gel par réaction en phase solide, tandis que les films minces ont été obtenus par pulvérisation cathodique rf-magnétron. Les caractérisations de leurs propriétés physiques confirment l'obtention de NiTiO3 polycristallin dans sa phase ilménite. La détermination du gap électronique à 2,25 eV suggère la faisabilité de mise en oeuvre des matériaux synthétisés comme photocatalyseurs actifs sous irradiation en lumière visible. Cette fonctionnalité a été testée par la dégradation du bleu de méthylène en solution aqueuse en utilisant les couches minces de NiTiO3 sous irradiation visible, atteignant la dégradation de 60% de la concentration initiale du colorant en 300 minutes. En outre, l'électro-oxydation du méthanol a été réalisée en appliquant une tension externe sur une électrode contenant des poudres NiTiO3 dans des milieux alcalins. Les ions de Ni présents dans le catalyseur ont été identifiés comme des espèces actives et que l'oxydation des molécules organiques se produit sur la surface des sites de Ni3+. En résumé, NiTiO3 a été synthétisé sous forme de poudres et de films minces ayant des caractéristiques appropriées pour la photocatalyse hétérogène efficace et les capacités catalytiques de NiTiO3 ont été démontrées sur la photodégradation du bleu de méthylène et l'électrooxydation de méthanol. / The thesis work is devoted to the synthesis of NiTiO3-based semiconductive structures, i.e. powders and thin films, and the investigation of their related properties with the aim of their applications in photocatalysis. Theoretical approach and numerical simulations of the electronic, vibrational and optical properties of bulk and nanosized NiTiO3 structures have been carried out in order to deepen the understanding of the experimental results. The synthesis of NiTiO3 powders has been achieved by sol-gel and solid state reaction, while NiTiO3 thin films have been grown by rf-sputtering.Characterizations on their structural, vibrational and optical properties confirm the stabilization of polycrystalline NiTiO3 in its ilmenite phase in both powders and thin films as well. The determination of a band gap at 2.25 eV suggests the feasibility to implement the synthesized materials as visible-light-active photocatalysts. This feature has been tested in thedegradation of methylene blue in aqueous solution using rf-sputtered NiTiO3 thin films irradiated with visible light,achieving the degradation of 60% of the initial concentration of the colorant in 300 minutes. In addition, the electro-oxidation of methanol has been accomplished by applying an external voltage on an electrode containing NiTiO3 powders in alkaline media. The Ni ions present in the catalyst have been identified as the active species with the oxidation of the organic molecules on the surface of Ni3+ sites. As a main achievement, NiTiO3 has been synthesized as powders and thin films with suitable characteristics for efficient heterogeneous photocatalysis and the catalytic capabilities of NiTiO3 have beendemonstrated on the photodegradation of Methylene Blue and the electro-oxidation of methanol.