Dissertations / Theses on the topic 'LaFeO₃'

L’hydrogène est un vecteur énergétique d’avenir en remplacement des hydrocarbures fossiles, à condition d’avoir une production majoritairement décarbonée. L’une des solutions les plus prometteuses pour générer l’hydrogène propre et durable est la décomposition photochimique de l’eau à partir de l’énergie solaire. Dans ce contexte, cette thèse porte sur l’élaboration et l’optimisation d’un photocatalyseur stable et composé d’éléments abondants. LaFeO₃ est un matériau pérovskite semi-conducteur présentant une excellente stabilité chimique et qui absorbe une large part visible du spectre solaire, mais ses propriétés photocatalytiques sont limitées par un faible transport des électrons. Pour améliorer son activité, une hétérostructure associant LaFeO₃ à g-C₃N₄ a été formée. g-C₃N₄ est un semi-conducteur organique 2D avec des propriétés optiques, structurelles et électroniques exceptionnelles. Leur association a permis d’augmenter significativement l’activité photocatalytique par une amélioration de la séparation et du transfert des porteurs de charge. Deux méthodes de production de H₂ ont été étudiées : par photocatalyse (PC) et photoélectrocatalyse (PEC). Les photoélectrodes du dispositif PEC ont été élaborées par pulvérisation cathodique magnétron et les nanoparticules dispersées en solution du dispositif PC ont été synthétisées par voie sol-gel. L’insertion d’une couche de g-C₃N4, déposée par spin-coating, sous le film de LaFeO₃ a permis pour la première fois de former cette hétérojonction en films minces, tandis que l’association par sonication des particules de LaFeO₃ et g-C₃N₄ a permis la création de l’hétérojonction en photocatalyseurs dispersés. L’influence de la composition des photoélectrodes a également été étudiée dans le cas de films non-stœchiométriques et par insertion d’éléments métalliques additionnels
Hydrogen is a promising energy carrier for replacing fossil fuels, under the conduction of having a mainly low carbon production. One of the most promising solution to generate clean and durable hydrogen is water splitting from solar energy. This manuscript focuses on the development and optimization of an abundant and stable photocatalyst. LaFeO₃ is a perovskite semi-conductor material showing and excellent chemical stability and that absorbs a large part in the visible spectra, although a low electron transfer limits its photocatalytic properties. To improve its activity, a heterostructure associating LaFeO₃ with g-C₃N₄ was realised. g-C₃N₄ is an organic semi-conductor with outstanding optical, structural, and electronic properties. Their association led to a significant increase in the photocatalytic activity by an increase in the separation and transfer of charge carriers. Two methods for H₂ production were studied: photocalysis (PC) and photoelectrocatalysis (PEC). Photoelectrodes of PEC dispositive were elaborated by magnetron sputtering and nanoparticles dispersed in solution of PC dispositive were synthesised using sol-gel. The insertion of a layer of g-C₃N₄, deposited by spin coating, below the LaFeO₃ films allowed for the first time to prepare this heterojunction using thin films, while the sonication of particles of LaFeO₃ and g-C₃N₄ allowed creating a heterojunction of dispersed photocatalysts. The impact of the composition of photoelectrodes was also studied for non-stoichiometric films and by inserting additional metallic elements

This work explores the hydrothermal synthesis of LaFeO3 (LFO) nanorods with a high aspect ratio. Synthesis of rod shaped LFO is a stepping stone to the synthesis of strontium doped LFO (LSF) nanorods with high aspect ratio. These LSF rods can be used to structure and increase the area of dense LSF oxygen permeable membranes, which can be applied in the partial oxidation of methane for the production of synthesis gas. Obtaining a larger surface area can increase the oxygen transport through the membrane when the transport is limited by surface exchange reactions. Increasing the oxygen transport is the objective of the work. LFO was attempted synthesised by a direct and a two-step synthesis. Product morphology and phase composition have been explored by the use of SEM and XRD. In the direct synthesis the effect of potassium hydroxide concentration, molar ratio of iron to lanthanum and synthesis duration were varied to investigate the effect of these parameters. LFO was not produced in the direct synthesis; the products consisted of La(OH)3 and Fe2O3. Since LFO was not obtained, a calculation exploring the temperature where LFO become more stable than La(OH)3 and Fe2O3 was performed. The calculations show that the transition temperature where LFO is thermodynamically favoured is close to the operating synthesis temperature. The small driving force for formation of LFO at a temperature close to the transition temperature is the reason why LFO have not formed in the direct syntheses.The two-step method consists of hydrothermal synthesis of La(OH)3 nanorods, which were covered by iron nitrate solution and attempted converted into LFO by a topochemical reaction. In the study performed, the rod structure is lost when the product is calcined at 400 ºC. LFO is not observed formed at this temperature, and LFO nanorods were therefore not obtained in the two-step synthesis.

O texto que segue apresenta, em perspectiva, a trajetória de atuação de Percival Lafer - designer e industrial brasileiro. Apesar de ter ficado à sombra da historiografia, o designer contribuiu enormemente para a formação do que podemos considerar hoje o mobiliário nacional, dentro do âmbito comum das definições sobre design ligado à produção industrial. A pesquisa lança bases para novos pensamentos acerca do modernismo e sua duração no tempo, bem como sobre a atuação de profissionais da arquitetura e desenho industrial durante os anos da ditadura militar brasileira. Delineia-se assim, um período da historiografia do design que pode ser considerado transitório - salto das bases produtivas artesanais ao movimento desgovernado da industrialização nacional. A organização de um panorama iconográfico, detalhadamente comentado, enseja delinear o processo de criação de Lafer e sua relação com outras instâncias de atuação. A reflexão sobre a especificidade da linguagem projetual voltada à indústria coloca frente a frente a concepção de Percival Lafer às demais tentativas, ainda atuais, de organização de um desenho propriamente industrial e moderno. Por último, apresentamos impressões sobre a falência do movimento moderno no Brasil e sua persistência discursiva frente as urgências e necessidade de um país que exige outra lógica de ordenação do mundo material.
The following text presents, under perspective, the work trajectory of Percival Lafer, brazilian designer and industrial. Despite having remained in the shadows of historiography, the designer have enormously contribute to the formation of what we today consider the \"national furniture\", within the scope of conceptual definitions about the design related to industrial production. The research lays foundations to new considerations regarding modernism and its endurance over time, as well as to the role of architecture and industrial design professionals during the years of the brazilian military dictatorship. It is therefore outlined a period of the design historiography that might be considered transitory, a moment of leap from the primary productive basis towards the unbridled movement of our national industrialization. The organization of a iconographic panorama, commented in details, aspire to outline the creative process of Lafer and its bonds with other instances of work. The reflexion about the specificity of a project language turned to the industry, confronts Percival Lafer conceptions to the other attempts, still very current, of organization of a design properly modern and industrial. At last, we present impressions over the failure of the modern movement in Brazil and its discursive persistence front the urgencies and needs of a country that demands a different logic of organization of the material world.

Perovskita de LaFeO3 sintetizadas pelo método de Pechini foram avaliadas como catalisadores para a reação de oxidação parcial do metano. Foi impregnado níquel por via úmida como fase ativa em concentrações de 15 e 30 %, sobre as perovskitas, 15NLF e 30NLF, respectivamente, e o seu efeito foi avaliado para a mesma reação. Foi realizado análises termogravimétricas (TGA/DTGA) nos precursores da perovskitas, constatando a sua formação a 650 °C. A análise de microscopia de varredura (MEV) foi realizada nas amostras da perovskita pura, sendo que em uma delas foi realizada um banho de ultrassom para diminuir o tamanho de suas partículas e avaliar este efeito na reação de POM. Análises de difração de raio X (DRX) mostraram que todas as amostras apresentam as mesmas propriedades cristalográficas, sendo que, nas amostras contendo níquel, o metal apresentou-se na forma de NiO. O tamanho dos cristais, cálculado através da equação de Scherer, foi na ordem de 20 nm. Este resultado apontou que o níquel impregnado não participa da estrutura perovskita, mas sim está sobreposto a esta. Através da microscopia eletrônica de transmissão (TEM) foi possível visualizar a dispersão da fase ativa na superfície óxida e tamanhos de partículas na ordem de 20 nm. A redução a temperatura programada (TPR) apresentou as temperaturas de redução de espécies níquel e de ferro, presente na perovskita, e permitiu compreender a atuação das espécies Ni+2 e Fe0 na formação de H2 e CO. Os testes catalíticos foram realizados a 700ºC e 750°C, a pressão atmosférica, para uma vazão de alimentação de 200 cm3.min-1. Os testes cataliticos mostraram que a conversão de H2 dobrou para perovskita Ni/LaFeO3 em relação a LaFeO3. O catalisador 15NLF apresentou melhor estabilidade que o catalisador 30NLF para a reação.
LaFeO3 perovskite synthesized by the Pechini method were evaluated for the partial oxidation reaction of methane. Nickel was impregnated as the active phase in concentrations of 15 and 30%, on perovskites, 15NLF and 30NLF, respectively, and its effect was evaluated for the same reaction. Thermogravimetric analyzes (TGA / DTGA) were carried out on the perovskite precursors, confirming their formation at 650 °C. Scanning microscopy (SEM) was performed on pure perovskite samples, in one of them an ultrasonic bath was performed to reduce the size of its particles and to evaluate this effect in the POM reaction. X-ray diffraction (XRD) analyzes showed that all samples had the same crystallographic properties, and in the samples containing nickel, the metal was present as NiO. The size of the crystals, calculated through the Scherer equation, was in the order of 20 nm. This result pointed out that the impregnated nickel does not participate in the perovskite structure. Through transmission electron microscopy (TEM) it was possible to visualize the dispersion of the active phase on the oxide surface and particle sizes in the order of 20 nm. The programmed temperature reduction (TPR) showed the iron and nickel species reduction temperatures present in the perovskite, and allowed to understand the Ni+ 2 and Fe0 species in the H2 and CO formation. The catalytic tests were performed at 700 °C and 750 °C at atmospheric pressure for a flow rate of 200 cm3.min-1. The catalytic tests showed that the conversion of H2 doubled to perovskite Ni/LaFeO3 in relation to LaFeO3. 15NLF catalyst presented better stability than the 30NLF catalyst for the reaction.

La dépollution des gaz d’échappement des véhicules essence est opérée par catalyse trois voies (CTV). Ce terme désigne la combinaison de trois réactions : l’oxydation du CO en CO2, la combustion des hydrocarbures imbrûlés et la réduction des NOx. Les catalyseurs 3-voies actuels sont constitués de nanoparticules de métaux nobles (Pt, Rh, Pd…) dispersés sur un support oxyde. En raison de leur prix élevés de nombreuse recherche vise à limiter leur utilisation. Utilisées depuis le milieu des années 70 en catalyse en tant que support, les pérovskites sont une alternative possible. Dans le cas de la catalyse trois voies, les capacités oxydo-réductrices intrinsèques du fer font de la pérovskite LaFeO3 (LFO) un candidat intéressant pour la réduction des NOx et l’oxydation du CO. A ce jour, les mécanismes réactionnels de même que les sites actifs de ce catalyseur sont inconnus. Il est donc important de les mettre en évidence pour permettre une amélioration rationnelle des activités et sélectivités des catalyseurs 3 voies de nouvelle génération. Dans cette étude nous avons cherché à déterminer le mécanisme réactionnel sur la pérovskite. Dans un premier nous avons cherché à étudier l’état de surface de la pérovskite en présence d’eau et déterminer les surfaces présentes. Puis nous avons calculé la thermochimie d’un ensemble de réaction élémentaire sur les surfaces pour enfin proposé un mécanisme réactionnel possible de réduction de NO et d’oxydation de CO. Après détermination des états de transition nous avons cherché à optimiser la formulation de la pérovskite en dopant les surfaces en métaux de transition
Pollution control of exhaust gases from gasoline vehicles is operated by three-way catalysis (TWC). This term refers to the combination of three reactions: the oxidation of CO to CO2, the combustion of unburned hydrocarbons and NOx reduction. Actually three-way catalysts are made of noble metal nanoparticles (Pt, Rh, Pd ...) deposed on an oxide support. Due to their high and fluctuating price numerous study are trying to limit their use. One possibility are perovskites which are used since the mid-70s in catalysis as support. These materials have also been a recent revival of interest as a carrier or as the active phase to the extent that their structural properties reduce the amounts of noble metals by limiting the aggregation of the metal nanoparticles. In the case of three-way catalysis, the redox intrinsic iron capabilities make the perovskite LaFeO3 (LFO) an interesting candidate for the reduction of NOx and oxidation of CO. To date, the reaction mechanisms, as well as the active sites of the catalyst are unknown. It is important to highlight them for rational improvement activities and selectivity of the catalysts 3 new generation pathways. In this study we sought to determine the reaction mechanism on perovskite. At first we tried to study the surface condition of the perovskite in the presence of water and determine these surfaces. Then we calculated the thermochemistry of a set of elementary reaction on surfaces to finally proposed possible reaction mechanism of NO reduction and CO oxidation. After determining transition states we sought to optimize the formulation of the perovskite by doping transition metal surfaces

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
The fuel cell are an alternative of production clean and efficient energy, because converts chemical energy in electrical energy. A fuel cell is formed basically by an electrolyte, a cathode and an anode. The fuel fed the anode and the oxidant fed the cathode. The fuel cells are classified according to the electrolyte used. The solid oxide fuel cell (SOFC) has all the components in solid state and work in high temperatures. The main electrolyte used for SOFC manufacturing is the ZrO2-Y2O3 owing your high ionic conductivity. The materials for electrode manufacturing must possess thermal expansion characteristics close to electrolyte and have high electrical conductivity in operating temperature, besides chemical and mechanical stability during operate and manufacture. High accomplishment cathodes have been studied, highlighting those with mixed conductivity, most ceramics with perovskite structure and lanthanide ions in your composition. Among these oxides, the perovskite LaFe1-xNixO3-δ has attracted interest for application as cathode in SOFC’s, to operate at intermediate temperatures. Chemical methods of production of ceramic powders are very efficient for obtaining powders with high reactivity and chemical homogeneity. Among the methods of chemical synthesis used to obtain powders, the Pechini method has pointed as a promising alternative process for obtaining nanometric powders. This work aimed to obtain LaFe1-xNixO3-δ powders by Pechini method, studying their behavior when changed processing conditions. The samples were synthetized, calcined and sintered. The characterizations accomplished were thermogravimetric analysis, differential thermal analysis, infrared spectroscopy, x-ray diffraction, scanning energy microscopy, spectroscopy dispersive energy, helium picnometry, surface area measured by BET method, density, porosity and water absorption by Arquimedes method, impedance spectropy and mercury porosimetry.Based on the characterizations performed, the LaFe1-xNixO3-δ obtained by the method based on the Pechini method proved viable for a possible application as cathode fuel cell solid oxide.
As células a combustível são uma alternativa à produção de energia elétrica limpa e eficiente, pois convertem energia química em energia elétrica. Uma célula a combustível é composta basicamente por um eletrólito, um cátodo e um ânodo. O combustível alimenta o ânodo e o oxidante alimenta o cátodo. As células a combustível são classificadas de acordo com o eletrólito utilizado. A célula a combustível de óxido sólido (CaCOS) tem todos seus componentes no estado sólido e opera em altas temperaturas. O principal eletrólito utilizado para a fabricação de uma CaCOS é o ZrO2-Y2O3 devido a alta condutividade iônica. Os materiais para a fabricação dos eletrodos devem possuir características de dilatação térmica próximas a do eletrólito e possuírem alta condutividade elétrica na temperatura de operação, além de estabilidade química e mecânica durante a operação e fabricação. Cátodos de alto desempenho vêm sendo estudados, chamando a atenção aqueles com condutividade mista, em sua maioria cerâmicos com estrutura perovisquita e com íons lantanídeo em sua composição. Entre esses óxidos, a perovisquita LaFe1-xNixO3-d tem atraído o interesse para a aplicação como cátodo nas CaCOSs, para operar em temperaturas intermediárias. Os métodos químicos de obtenção de pós cerâmicos são muito eficientes para a obtenção de pós com alta reatividade e homogeneidade química. Dentre os métodos de síntese química utilizados para a obtenção de pós, o método Pechini tem se destacado como um processo alternativo e promissor para a obtenção de pós nanométricos. Este trabalho teve como objetivo obter pós de LaFe1-xNixO3-d por meio do método Pechini, estudando seu comportamento quando alteradas condições de processamento. As amostras foram sintetizadas, calcinadas e sinterizadas. As caracterizações realizadas foram análise termogravimétrica, análise térmica diferencial, espectrometria no infravermelho, difração de raios x, microscopia eletrônica de varredura, espectrometria de energia dispersiva, picnometria a hélio, medida de área superficial pelo método BET, medidas de densidade, porosidade e absorção de água pelo método de Arquimedes, espectroscopia de impedância e porosimetria de mercúrio. Com base nas caracterizações realizadas o LaFe1-xNixO3-d obtido pelo método baseado no método Pechini, mostrou-se viável para uma possível aplicação como cátodo de células a combustível de óxido sólido.

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The present paperwork aims at looking over the political debate at the 1946 constituent, from the view of the economical crisis figured by the end of the war and the consequent finish of the New State Dictatorship, aiming at understanding the impasses and dilemmas faced by the political actors upon the necessity of reorganization of the institutional frame concerning the economic policy. The liberal though was facing the hard task of redefining the huge presence of the State in the Brazilian economy e society. The debate upon the development of the industry was a guidance axle of the disputes observed in the Constituent. The study is based on Horacio’s Lafer ideas, considering him as a link between the two political experiences. The analysis of the parties, especially of the position taken upon the differences faced in the process of democracy rebuilding, was seen with attention by following the chancing process and continuation which characterized President Dutra’s administration.
O presente trabalho tem por finalidade refletir sobre o debate político na constituinte de 1946, a partir do quadro de crise econômica configurado pelo fim da guerra e o conseqüente derrocada da Ditadura Estadonovista, visando compreender os impasses e dilemas enfrentados pelos atores políticos diante da necessidade de reordenação do quadro institucional no que diz respeito à política econômica. O pensamento liberal estava diante da complexa tarefa de redefinir a enorme presença do Estado na economia e na sociedade brasileira. O debate em torno do desenvolvimento da indústria foi um dos eixos das contendas observadas em meio a Constituinte. O estudo se deteve no pensamento de Horácio Lafer, entendendo-o como uma ponte entre as duas experiências políticas. A análise dos partidos, em especial da posição assumida diante dos impasses enfrentados no processo de reconstrução democrática, foi objeto de nossa atenção ao acompanhar o processo de mudanças e continuidades que caracterizaram o governo do presidente Dutra.

Les travaux de thèse ont porté sur la substitution cationique et anionique du composé LaFeO3, élaboré en couche mince par pulvérisation cathodique magnétron réactive (deux cibles métalliques et mélange gazeux Ar+O2). La première partie de la thèse est consacrée à la substitution du lanthane par d'autres terres rares plus petites : Praséodyme, Néodyme et Samarium. Les quatre pérovskites LaFeO3, PrFeO3, NdFeO3 et SmFeO3 ont donc été synthétisées et caractérisées (caractérisations optiques, électriques et structurales), et l'influence de la substitution sur les propriétés physiques est discutée. Les travaux ont montré que la substitution du lanthane par d’autres terres rares plus petites entraîne une modification des propriétés, que nous pouvons directement relier à la distorsion de la maille. Dans une deuxième partie, le dopage à l’azote du composé LaFeO3 a été réalisé, en utilisant de l'azote en tant que gaz réactif (deux cibles + mélange gazeux Ar+O2+N2). Les conditions de dépôt ont été étudiées dans le but d'optimiser la synthèse. A partir de mesures in situ des paramètres de la cible en fonction des débits de gaz, associées aux mesures post dépôt (composition, épaisseur, conductivité électrique), des conditions particulières de synthèse ont été retenues, afin d’optimiser le dopage à l’azote. L’utilisation de ces conditions de synthèses spécifiques ont permis la réalisation de plusieurs dépôts LaFeO3-xNx qui ont ensuite été caractérisés (caractérisations chimiques, optiques, électriques et structurales). Il en résulte que le dopage à l’azote du composé LaFeO3 entraîne une modification du gap de la pérovskite, ainsi que des propriétés électrique, et optique, malgré une faible teneur en azote
The work done trough this PhD deals with cationic and anionic substitution of LaFeO3 thin films deposited by reactive magnetron sputtering (co-sputtering of two targets in Ar+O2 mixture). The first part of the word is devoted to substitution of lanthanum by smaller rare earth, Praseodymium, Neodymium, and Samarium. The four perovskites LaFeO3, PrFeO3, NdFeO3 and SmFeO3 have been synthesized and characterized (optical, electrical and structural properties), and this cationic substitution is discussed. It results in a shift of the properties which can be directly linked with lattice distortion due to smaller rare earth. In a second part, nitrogen doping of LaFeO3 has been studied, by using nitrogen as reactive gas (co-sputtering of two targets in Ar+O2+N2 mixture). Deposition conditions have been studied in order to optimize the perovskite synthesis. From in situ measurements of target voltage variation with flow rate associated to post-deposition measurement (thickness, composition, electrical conductivity), specified conditions have been found for nitrogen doping optimization. Different LaFeO3-xNx thin films have been deposited following these specified conditions, and characterized (chemical, optical, electrical and structural analysis). Nitrogen doping of LaFeO3 leads to bandgap decrease, associated to modification of optical and electrical properties, even if a small amount of nitrogen can be added to the structure

Compte tenu de considérations environnementales les matériaux multiferroïques sans plomb de type BixTR1-xFeO3 (TR :La, Sm, Dy) constituent une alternative de choix au PbZrxTi1-xO3 (PZT) pour l'utilisation dans des systèmes transducteurs. En effet, il a récemment été observé, dans ces composés, d'importantes propriétés piézoélectriques en relation avec une zone de phase morphotropique (ZPM) qui agirait comme un pont structural entre la phase R3c et la phase Pnma. Cette ZPM présente une variété de structures (adaptive, antiferroélectrique, incommensurable) et de propriétés encore largement incomprises. Notre approche pour mieux comprendre ces systèmes repose sur la synthèse et l'étude de super-réseaux à base de BiFeO3 et LaFeO3 (BFO/LFO). Les principales étapes de ce travail ont donc porté sur l'élaboration par ablation laser et la caractérisation structurale (par diffraction de rayons X, microscopie électronique en transmission et spectroscopie Raman) de super-réseaux de BFO(1-x)Λ/ LFOxΛ et de BFO0,5Λ/LFO0,5Λ. L'étude à température ambiante sur ces super-réseaux a démontré l'existence d’une structure antiferroélectrique de type PbZrO3 dans les couches de BFO. Cette phase anti-polaire présente un domaine de stabilité bien précis puisque une modification structurale vers une phase non polaire de type Pnma a pu être mise en évidence via la modification des proportions relatives dans la période ou du nombre d'interfaces. Les études en température ont par ailleurs démontré une transition de phase structurale de la phase anti-polaire type PbZrO3 vers une phase paraélectrique de type Pnma à haute température. Une modulation importante de la Tc en fonction de l'épaisseur de BFO dans la période montre le rôle important des contraintes. Cependant l'existence de contraintes seules ne peut expliquer cette phase antiferroélectrique. La compatibilité des systèmes de tilt et de rotation des octaèdres d'oxygènes aux interfaces des super-réseaux peut expliquer l'apparition de cette phase
Due to environmental issue the lead free multiferroic system Bi1-xTRxFeO3 (TR :La, Sm, Dy) constitute an alternative to PbZrxTi1-xO3 (PZT) widely used in transducers. Indeed, it was recently observed in these compounds an important piezoelectric properties linked to a morphotropic phase boundary (MPB), which acts like a bridge between R3c and Pnma phases. This MPB shows a variety of structure (adaptive, incommensurate, antiferroelectric) and properties that are not understood yet. Our approach to better understand this system lies on the growth and characterization of superlattices based on BiFeO3 and LaFeO3 (BFO/LFO). The principal steps of this work were the growth by pulsed laser deposition and the structural characterization (X-ray diffraction, transmission electron microscopy, Raman spectroscopy) of BFO(1-x)Λ/LFOxΛ and BFO0,5Λ/LFO0,5Λ superlattices. Room temperature structural investigations reveal the existence of PbZrO3 like anti-polar ordering in BFO layers. The anti-polar order presents specific domain stability and an induced structural modification toward a Pnma state is observed depending on the relative ratio x in the period and the number of interfaces. Temperature-dependent investigations demonstrate a structural phase transition from the PbZrO3 like anti-polar order to the Pnma like paraelectric structure at high temperature. An observed scaling of the Tc with the BFO thickness highlights the role of the strain. However strain only cannot explain the observed antiferroelectric like state and oxygen octahedral tilt compatibility at the interfaces of the superlattices must be taken into account

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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.

This study will focus on strain induced by thermal history and thickness on antiferromagnetic epitaxial LaFeO3(110) thin films grown on Nb:SrTiO3(001) substrates. Lattice mismatching between film and substrate induce strain in the film lattice during growth of the film. This strain can be relaxed by thermal treatment after growth and may show tendencies in the domain size, shape and distribution related to strain. Thin films are grown in different thicknesses by rf magnetron sputtering and selected films are relaxed by thermal anneal treatment. The samples are investigated in room temperature and in heating experiments to obtain images of antiferromagnetic domain contrast along the L2 and L3 absorbtion egde of Fe by XMLD spectromicroscopy. Size of domains areas and contrast level are measured and related to the strain in the thin films. Averaged spectra of L2 absorbtion edge antiferromagnetic contrast showed a clearly observable domain contrast with consistently shaped energy spectrums. No difference in antiferromagnetic contrast due to lattice strain caused by lattice mismatching was observed. All as-grown samples showed comparable size, distribution and shape of antiferromagnetic domains on both polished and etched substrates. Relaxation of prepared samples in 1000±C for 12 hours in a 1 atm atmosphere of oxygen gave a distinct increase in size for the domains. Area calculation show a increase from typically 0.2 ¹m2 for as-grown films to 2 ¹m2 for relaxed films. Heating experiments estimate a Néel temperature of 625oK for as-grown films and 740oK for relaxed samples. The thermal anneal thus has a significant effect on LaFeO3 thin films as the domains increase in size and the Néel temperature in which the film is no longer antiferromagnetic increases to the Neel temperature of bulk LaFeO3. This preparation approach may be useful for further investigations of the exchange-bias effect.

L'intercalation électrochimique de l'oxygène est examinée pour des ferrites de calcium et de strontium de structures derivees de la perovskite. Les résultats montrent que les ferrites contenant du strontium peuvent être effectivement oxydes; tel n'est pas le cas de ceux contenant du calcium. Ceci peut étre expliqué par des considérations énergétiques relatives au processus de diffusion de l'oygéne, sur la base de données cristallographiques et d'un modèle ionique. Par ailleurs la perovskite Sr₂LaFe₃O8. 95 a été préparée par oxydation électrochimique et plus particulièrement caratérisée tant du point de vue structural que de ses propriétés physiques : propriétés magnétiques et de transport, résonance, Mössbauer, propriétés thermodynamiques, transition de phase électronique.

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Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico
Materials consisting of perovskite-type oxides (ABO3) have been developed in this work for applications in fuel cell cathodes of solid oxide type (SOFC). These ceramic materials are widely studied for this type of application because they have excellent electrical properties, conductivity and electrocatalytic. The oxides LaMnO3, LaFeO3, LaFe0.2Mn0.8O3 e La0.5Fe0.5MnO3 were synthesized by the method of microwave assisted combustion and after sintering at 800?C in order to obtain the desired phases. The powders were characterized by thermogravimetry (TG), X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and voltammetric analysis (cyclic voltammetry and polarization curves). The results obtained by XRF technique showed that the microwave synthesis method was effective in obtaining doping oxides with values near stoichiometric. In general, powders were obtained with particle size less than 0.5 μm, having a porous structure and uniform particle size distribution. The particles showed spherical form, irregular and crowded of varying sizes, according to the analysis of SEM. The behavior of the oxides opposite the thermal stability was monitored by thermogravimetric curves (TG), which showed low weight loss values for all samples, especially those of manganese had its structure. By means of Xray diffraction of the samples sintered at 800?C was possible to observe the formation of powders having high levels of crystallinity. Furthermore, undesirable phases such as La2O3 and MnOx were not identified in the diffractograms. These phases block the transport of oxygen ions in the electrode/electrolyte interface, affecting the electrochemical activity of the system. The voltammetric analysis of the electrocatalysts LF-800, LM-800, LF2M8-800 e L5F5M-800 revealed that these materials are excellent electrical conductors, because it increased the passage of electrical current of the working electrode significantly. Best performance for the oxygen reduction reaction was observed with iron-rich structures, considering that the materials obtained have characteristics suitable for use in fuel cell cathodes of solid oxide type
Materiais constitu?dos de ?xidos do tipo perovskita (ABO3) t?m sido desenvolvidos no presente trabalho para aplica??es em c?todos de c?lulas a combust?vel do tipo ?xidos s?lidos (SOFC). Estes materiais cer?micos s?o amplamente estudados para esse tipo de aplica??o porque apresentam ?timas propriedades el?tricas, condutoras e eletrocatal?ticas. Os ?xidos LaMnO3, LaFeO3, LaFe0,2Mn0,8O3 e La0,5Fe0,5MnO3 foram sintetizados pelo m?todo de combust?o assistida por microondas e logo ap?s sinterizados a 800?C a fim de obter as fases desejadas. Os p?s obtidos foram caracterizados por termogravimetria (TG), difratometria de raios-X (DRX), fluoresc?ncia de raios-X (FRX), microscopia eletr?nica de varredura (MEV) e an?lise voltam?trica (voltametria c?clica e curvas de polariza??o). Os resultados obtidos atrav?s da t?cnica de FRX evidenciam que a escolha do m?todo de s?ntese por microondas foi eficaz na obten??o de ?xidos com valores de dopagens pr?ximos ao estequiom?trico. No geral, foram obtidos p?s com tamanho de part?culas inferiores a 0,5 μm, apresentando estrutura porosa e distribui??o de part?culas uniformes. As part?culas se apresentaram na forma esf?rica, irregular e aglomerada de tamanhos variados, segundo a an?lise de MEV. O comportamento dos ?xidos frente ? estabilidade t?rmica foi monitorado atrav?s das curvas termogravim?tricas (TG), a qual mostrou baixos valores de perdas de massa para todas as amostras, principalmente aquelas que apresentavam o mangan?s em sua estrutura. Por meio da difratometria de raios-X das amostras sinterizadas a 800?C foi poss?vel observar a forma??o de p?s com elevados valores de cristalinidade. Al?m disto, fases indesej?veis como La2O3 e MnOx, n?o foram identificadas nos difratogramas. Estas fases bloqueiam o transporte de ?ons oxig?nio na interface eletrodo/eletr?lito, comprometendo a atividade eletroqu?mica do sistema. A an?lise voltam?trica dos eletrocatalisadores LF-800, LM-800, LF2M8-800 e L5F5M-800 demonstrou que estes materiais s?o ?timos condutores, porque aumentaram a passagem de corrente el?trica do eletrodo de trabalho de forma significativa. Melhor desempenho para a rea??o de redu??o de oxig?nio foi observado com estruturas ricas em ferro, considerando que os materiais obtidos possuem caracter?sticas apropriadas para aplica??o em c?todos de c?lulas a combust?vel de ?xidos s?lidos

碩士
國立中央大學
環境工程研究所
106
Volatile organic compounds (VOCs) are important air pollutants emitted from industrial, domestic and natural sources. Toluene and isopropanol (IPA) are VOCs which are commonly used in industrial manufacture. Typical technologies including adsorption, absorption, and combustion have been employed to eliminate VOCs from gas streams. Recently, photocatalysis is regarded as a potential way for the removal of VOCs. TiO2 is the most common photocatalyst in the photocatalysis field and also the most likely to be applied in industrial scale, due to its non-toxicity, abundance and photo/chemical stability. However, TiO2 has some limits including it has fast recombination rate of electron-hole pair and only absorbs UV light. Therefore, in this study, removal of toluene and IPA were investigated using black-TiO2 catalyst. Black-TiO2 can absorb visible light and has more defects on the catalyst surface. In this study, we discuss the conversion rate of VOCs by black-TiO2. The results, indicate that 98% and 89% conversion rate can be achieved for IPA and toluene, respectively. As the oxygen content is increased, the conversion rate also increases. As flow rate and hydrogen concentrations are increased, the conversion rate decreases. The results indicate higher removal efficiencies can be achieved with black-TiO2 when compared with TiO2 and LFO/black-TiO2. Overall, the preliminary results indicate that black-TiO2 can enhance the performance of photocatalysis system for toluene and IPA removal.

碩士
國立臺北科技大學
化學工程與生物科技系化學工程碩士班
106
In recent past perovskite oxides and their derivatives comprise a large family of promising semiconductor materials because of their structural simplicity and flexibility, good stability and efficient catalytic performance. The perovskite material requires metal oxides that supports to enhance the catalytic activity which is cost effective and Heat resistance that is increased to use by many scientists. In this study, the One-dimensional perovskite arrays are prepared by Anodic Aluminum Oxide(AAO). The different ratio of LaFe1-xMnxO3 (x=0, 0.5, 1) were characterized using in situ FTIR (DRIFT) which can observe the adsorption of carbon monoxide and nitrogen oxides on the transition of perovskite-type Catalyst. And also we have discussed the gas phase reaction by using Gas Cell-FTIR, which not only observe the NO, NO2 , N2O4, also observe the N2O , N2O3. Further, we studied the changes with different temperature. Finally, we have calculated the CO conversion rate by the GC with TCD. The as-prepared perovskite-type LaFe1-xMnxO3 catalyst was observed by X-ray Diffraction (XRD) to know the structure of the perovskite and its crystalline. The surface morphology of perovskite materials with high magnification and low magnification was confirmed by SEM and FESEM respectively. The EDS to ensure the element content in the perovskite material. The Photoluminescence was used to identify the energy band gap of perovskite material.

As quedas são uma das maiores dificuldades vividas pelos idosos. Estas são a maior causa de lesões e traumas dentro da faixa etária da terceira idade, e isto acoplado ao tempo que os idosos esperam por socorro aumenta o risco de morbilidade e incapacidade nos mesmos. Para tentar solucionar o problema das quedas vamos tirar partido de uma tecnologia recente e de alto nível que é o Wiimote. Este dispõe entre outras coisas de um acelerómetro e através do processamento da aceleração é possível detectar quedas e identificar as diferentes Actividades de Rotina Diária (DRA). Assim o AAL Safe consiste numa prova de conceito que tem como objectivo ser uma solução dinâmica e útil, virada para o utilizador e que monitoriza a sua rotina diária em tempo real e acima de tudo detecta situações de risco como é o caso das quedas, melhorando deste modo o estilo de vida de um idoso. Este documento tem como objectivo descrever o sistema e explicar as diferentes fases do seu desenvolvimento

Transition metal oxides have proven to be a fertile research area for condensed matter physicists due to the fascinating array of superconducting, magnetic and electronic properties they exhibit. A particular resurgence of intense activity in investigating the properties of these systems followed the discovery of high temperature superconductivity in the cuprates, colossal magnetoresistance in the manganites, ferroelectricity in the cobaltites and simultaneous ferroelectric and ferromagnetic ordering in the manganites. These diverse properties of transition metal compounds arise due to the presence of strong electron-electron interactions within the transition element 3d states. Indeed, it is the competition between the localizing effects of such interactions and the comparable hopping strengths driving the system towards delocalization, that is responsible for these wide spectrum of interesting properties. In terms of theoretical and fundamental issues, electronic structure of transition metal oxides play a most important role, providing a testing ground for new many-body theoretical approaches treating the correlation problem at various levels of approximations. In addition to this rich spectrum of properties, metal-insulator transitions often occur and can even be coincident with structural or magnetic changes due to the strong coupling between charge, magnetic and lattice degrees of freedom. However, in spite of the immense activities in this area, the underlying phenomena is not yet completely understood. A careful investigation of the electronic structure of these systems will help in the microscopic understanding of these and photoelectron spectroscopy has been established as the most powerful tool for investigating the electronic structures of these systems. In this thesis we investigate the electronic structures of some of these transition metal oxides and the metal-insulator transition as a function of electron correlation strength and doping of charge carriers by means of photoelectron spectroscopy; we analyze the experimental results using various theoretical approaches, in order to obtain detailed and quantitative understandings. This thesis is organized into seven chapters. Chapter 1 is a general introduction to the various concepts discussed in this thesis. Here we briefly describe the various mechanisms and theoretical formalisms used for understanding the metal-insulator transitions in strongly correlated systems and the evolution of the electronic structure across the transition. The experimental and the calculational techniques used in this thesis is described in Chapter 2. This includes different sample synthesis techniques and the characterization tools used in the present study. Photoelectron spectroscopic techniques used for probing the electronic structure of various systems are also discussed in this chapter. In Chapter 3, we discuss the coexistence of ferromagnetism and superconductivity in ruthenocuprates by looking at the electronic structures of RuSr2Eu1.5Ce0.5Cu2O10 which is a ferromagnetic superconductor having the ferromagnetic TC ~ 100 K and a superconducting transition of ~ 30 K compared with RuSr2EuCeCu2O10 which is a ferromagnetic (TC ~ 150 K) insulator in conjunction with two reference systems, RuSr2GdO6and Sr2RuO4. The coexistence of ferromagnetic order with superconductivity below the superconducting temperature is an interesting issue since the pair-breaking due to magnetic interactions is not significant in these cases. Extensive photoelectron spectroscopic measurements were performed on these systems and our results show that Eu and Ce in both the ruthenocuprates exists in 3+ and 4+ states, respectively. Also the analysis of the Ru 3d and 3p core levels suggests that Ru remains in the pentavalent state in both the cases. The constancy of Ru valency with doping of charge carriers that bring about an insulator to metal transition and the superconducting state suggests that the electronic structure and transport properties of these compounds are not governed by the Ru-O plane, but by the Cu-O plane, much as in the case of other high TC cuprates. Analysis of the Cu 2p core level spectra in terms of a cluster model, including configuration interaction and multiplet interactions between Cu 3d and 2p as well as that within the Cu 3d states, establish a close similarity of the basic electronic structure of these ruthenocuprates to those of other high TC cuprates. Here the charge transfer energy, Δ << Udd,Cu 3d multiplet-averaged Coulomb repulsion energy, establishing the compounds to be deep in the charge transfer regime. Continuing with the ruthenocuprate systems in Chapter 4, we look at the electronic structure of hole doped La2CuRuO6systems using various photoemission techniques. It was expected that since the substitution of La3+by Sr2+changes the d electron count, the system will undergo a metal to insulator transition, but the transport properties show that all of them remain semiconducting through out the lowest temperature of measurement. A careful analysis of the Ru 3d and 3p core level spectra shows that Ru exists in Ru 4+state in La2CuRuO6and goes towards Ru 5+state with hole doping. This suggests that the doped holes affects the electronic structure of the Ru levels in these systems. A spectral decomposition of the Ru 3d core level suggests the existence of a spin orbit split doublet having two peaks, a main core level peak and a satellite peak at the higher binding energy side of the main peak and the intensity ratio of the satellite peak to the main peak increases with the insulating nature of the compounds as reported for other Ru 4d strongly correlated systems. This observation is also consistent with the transport properties. Cu 2p core level spectra also shows variations in the satellite-to-main peak Cu 2p intensities suggesting that the electronic structure of the Cu levels are also getting affected with Sr doping. Valence band spectral features near the Fermi level shows that the spectral weight is highest for La2CuRuO6and depletes slowly with Sr doping consistent with the expected d electron count as suggested by the Ru valencies. In Chapter 5 and Chapter 6 we discuss the electronic structure investigations of two early transition metal oxide series, namely Ca1−xSrxVO3and Ce1−xSrxTiO3. Surface sensitivity dependence of photoemission experiments has been explored to show that the surface and the bulk electronic structures of Ca1−xSrxVO3system is different. Photoemission spectra of this system using synchrotron radiation reveal a hither to unnoticed polarization dependence of the photoemission matrix elements for the surface component leading to substantial underestimation. Extracted bulk spectra from experimentally determined electron escape depth and underestimation of surface contributions resolve the puzzling issues that arose due to the recent diverse interpretations of the electronic structure in Ca1−xSrxVO3. Keeping in mind the above-mentioned caveat, the present results still clearly establish that the linear polarization of synchrotron radiation plays a key role in determining the spectral lineshape in these systems. The experimentally-determined bulk spectra provide an understanding of the electronic structure in Ca1−xSrxVO3, consistent with experimental γ values, calculated change in the d-bandwidth and the geometrical/structural trends across the series, thereby resolving the puzzle concerning the structure-property relationship in this interesting class of compounds. In Chapter 6 we discuss the issues of metal-insulator transition close to the d0limit as well as the evolution of the electronic structure of a strongly correlated system as a function of electron occupancy, by investigating the family of Ce1−xSrxTiO3compounds by recording core level as well as valence band photoemission spectra using lab source as well as synchrotron radiations. Core level Ce 3d spectra from Ce1−xSrxTiO3samples establish a trivalent state of Ce in these compounds for all values of x confirming that charge doping in the present system does not alter the electronic structure of Ce. Hence the change in valency due to Sr substitution and thus, the carrier number, takes place only in the Ti 3d-O 2p manifold. We also carried out extensive VUV photoemission experiments on these samples with the photon energy varying between 26-122 eV. From the difference spectrum obtained by subtracting the off-resonance spectrum from the on-resonance one, we obtain the Ce 4f spectral signature; thus obtained Ce 4f spectrum which has a peak at about 3 eV binding energy and shows no intensity at EF even for the metallic samples, consistent with a Ce3+state. In order to study the states near EF responsible for the metal-insulator transition in these compounds, we recorded the valence band spectra at the Ce 4f off-resonance condition so that the coherent and the incoherent spectral features arising from the Ti 3d states could be clearly resolved, allowing us to investigate the metal insulator transition in the Ce1−xSrxTiO3system as a function of Sr or hole doping. The experimental spectra of the metallic compounds exhibit an intensity of the incoherent feature considerably larger than that predicted by theory. This discrepancy is possibly due to a difference in the surface and the bulk electronic structures of these compounds. Chapter 7 is divided into two parts. In the first part we discuss the extended x-ray absorption fine structure (EXAFS) studies performed on two transition metal oxide series, La1−xSrxCoO3and La1−xSrxFeO3to look at the local structure distortions happening around the transition metal ions and its role in bringing out metal to insulator transitions in transition metal oxide systems. Here we chose to investigate these two systems since La1−xSrxCoO3undergoes an insulator to metal transition for x ∼ 0.15 and La1−xSrxFeO3remains insulating for the entire range of doping. The static mean square relative displacement, which we believe to be a representation of the disorder present in the system, extracted by fitting the experimental data by a correlated Einstein model, as a function of composition in La1−xSrxCoO3saturates beyond the critical composition where as the disorder parameter continues to increase through out the entire doping range in the case of La1−xSrxFeO3where metal-insulator transition is absent. In the second part of Chapter 7 we discuss the x-ray absorption near edge structure (XANES) studies performed on the above mentioned series of systems. Co K-edge XANES spectra of La1−xSrxCoO3show that there is a systematic shift of the main absorption peak with hole doping suggesting that the Co valency changes systematically with Sr doping. Also, the pre-edge feature of LaCoO3shows the transitions to t2g level clearly showing that Co3+in LaCoO3is not in a pure low spin (t6 2g) state. The Fe K-edge XANES spectra of La1−xSrxFeO3also exhibit a systematic shift to the higher energy side with increase in Sr content, indicating an increase in the Fe valence. Also from the La L3edge analysis, it can be concluded that the oxygen environment around La and the electronic configuration of La are systematically changing with Sr doping.