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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

The Studies of Powder Formulation and Thermal Treatment Parameters of Low Firing ZnO-based Varistor

Chien, Shih-feng 25 August 2006 (has links)
In this thesis, the powder formation and thermal treament parameters for low temperature firing of zinc oxide(ZnO) based multi-layered varistors are studied. Vanadium oxide(V2O5) was used as electrical former, and manganese oxide(MnOx), coblt oxide(CoOx) and other additives were used as electrical modifiers. The object of this thesis is to investigate the effects of additives on the electrical characteristics of ZnO varistors. Meanwhile, the parameters of thermal treament process of raw materials on the effects of low temperature cofiring of ZnO varistors are also studied. As a result, we found that V2O5 can lower the sintering temperature of ZnO-based varistor as low as 900¢J. Forthuremore, prolonged sintering duration and reduced ZnO particle size might lower the sintering temperature futher to a given temperature which makes it possible to co-fire the ceramic body, inner electrodes and outer electrodes. The formulation of powder with added 0.3mol%Mn3O4, 0.5mol%CoO and 0.1mol%Bi2O3 can obtain a high £\value of 24 and leakage current of 2£gA. Besides, we also found that the thermal treament of powder can affect the shrinkage or diffusion of inner electrodes in multi-layered ZnO varistor shape dramastically. Without thermal treament or inproper thermal treament conditions will cause the inner electrode over-shrinkaged or even disppeared. According to the results of experiment, 350~400¢Jand a longger period (4 hours and above) will improve the phenomenon of over -shrinkaged.
2

Catalytic properties of V2O5/SnO2 towards vapour-phase Beckmann rearrangement of cyclohexanone oxime

Pillai, SK, Gheevarghese, O, Sugunan, S 31 October 2008 (has links)
A B S T R A C T V2O5/SnO2 solid acid catalysts have been employed for the vapour-phase Beckmann rearrangement of cyclohexanone oxime to e-caprolactam. Catalysts with different vanadia loading (3–15 wt%) were prepared by impregnation method and characterized by XRD, BET surface area, FTIR and 51V NMR techniques. The surface acidic properties were determined by temperature programmed desorption and cumene cracking reaction. Under optimized reaction conditions, catalyst with 9 wt% V2O5 gives the maximum amount of desired product (yield 78.8%). However, the catalysts are susceptible for deactivation due to the basic nature of the reaction products (50% deactivation in 5 h). A good correlation was obtained among the rearrangement activities of V2O5/SnO2 catalysts, their weak plus medium acidities (usually of the Bro¨ nsted type) and structural properties.
3

Influência do hidrocloreto de polialilamina e nanopartículas de prata na eletro-inserção de íons lítio em matrizes hospedeiras de V2O5 / Poly(allylamine hydrochloride) and silver nanoparticles influence on the lithium ions electro-insertion in V2O5 host matrix.

Silva, Nelson Alexandre Galiote 05 May 2011 (has links)
Materiais automontados de V2O5, polialilamina (PAH) e nanopartículas de prata (AgNP) foram preparados pelo método camada-por-camada, visando a sua aplicação em baterias de íon-lítio e dispositivos eletrocrômicos. O método adotado permitiu o crescimento linear de filmes visualmente homogêneos de V2O5, V2O5/PAH e V2O5/PAH/AgNP com 15 bicamadas, como observado a partir de microscopia eletrônica de varredura (MEV) e espectroscopia eletrônica na região do visível. De acordo com os espectros de infravermelho com transformada de Fourier (FTIR), verificou-se que a interação entre o oxigênio do grupo vanadila e o grupo amino deve ser responsável pelo crescimento destes filmes, além de permitir uma blindagem eletrostática entre os íons lítio e os sítios com maior densidade de carga negativa, aumentando a velocidade difusional e, consequentemente, aumentando a capacidade de armazenamento de energia e diminuição do tempo de resposta. Resultados eletroquímicos e espectroeletroquímicos mostraram que a presença das AgNPs estabilizadas no PAH aumentou a capacidade de carga do eletrodo, propiciando novos caminhos condutores e aumentando o número de sítios eletroativos na matriz hospedeira. Espontaneamente, novas nanoarquiteturas com interações específicas foram formadas pelo método camada-por-camada, garantindo uma maior velocidade de transporte de massa e transferência de carga em eletrodos para baterias de lítio e dispositivos eletrocrômicos. / Self-assembled Materials from V2O5, polyallylamine (PAH) and silver nanoparticles (AgNP) were prepared by layer-by-layer method, aiming at its application in lithium-ion batteries and electrochromic devices. The adopted method allowed the linear growth of visually homogeneous films from V2O5, and V2O5/PAH, V2O5/PAH/AgNP with 15 bilayers. This was observed from scanning electron microscopy (SEM) and electronic spectroscopy in the visible region. According to the Fourier transform infrared (FTIR) spectra, it was found that the interaction between vanadyl groups oxygen and the amino group should be responsible for the growth of these films. Besides, this interaction allowed an electrostatic shield between the lithium ions and the sites with higher negative charge, increasing the ionic speed and diffusion, thereby increasing energy storages capacity and response times reduction. Electrochemical and spectroelectrochemical results showed that the presence of AGNPs stabilized in PAH increased the electrodes capacity, providing new path-ways and increasing the number of electroactive sites in the host matrix. Spontaneously, new nanoarchitectures to specific interactions were formed by the layer-by-layer method, ensuring a higher rate of mass transport and charge transfer in electrodes for lithium batteries and electrochromic devices application.
4

Dessulfurização oxidativa do dibenzotiofeno catalisada por V2O5 suportado / Oxidative desulfurization of dibenzothiophene catalyzed by supported V2O5

Débora Gomes Baptista Dionizio 16 September 2014 (has links)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A necessidade de redução da emissão de poluentes, visando diminuir os sérios problemas de poluição atmosférica enfrentados atualmente, é hoje uma das principais preocupações mundiais, provocando o surgimento de leis mais rígidas, que restringem o teor de enxofre na gasolina e no diesel. Assim, o desenvolvimento de tecnologias mais eficazes na remoção de enxofre nestes combustíveis tem recebido atenção crescente. Estas tecnologias incluem a extração física com solvente, a adsorção seletiva, processos de redução/oxidação microbiológicos e a dessulfurização oxidativa (ODS). A dessulfurização oxidativa converte os compostos de enxofre em sulfonas que podem ser facilmente separadas por processos físicos. Portanto, a ODS apresenta grande potencial para tornar-se um processo complementar a processo de hidrodessulfurização tradicional na produção de combustíveis altamente dessulfurizados. Neste contexto, este trabalho visou o estudo do desempenho de catalisadores de V2O5 suportados em alumina, sílica e sílica-alumina frente à reação de ODS do dibenzotiofeno em presença do peróxido de hidrogênio, como oxidante, e da acetonitrila, como solvente polar aprótico. Os catalisadores foram preparados por impregnação ao ponto úmido e caracterizados por difração de raios-X (DRX), análise textural, redução à temperatura programada (TPR-H2), dessorção de amônia à temperatura programa (TPD-NH3) e espectroscopia Raman. O efeito de parâmetros reacionais como quantidade de solvente, relação O/S e concentração de catalisador foram investigados, utilizando a alumina como suporte, visando estabelecer as condições reacionais que levassem a maiores valores de conversão do dibenzotiofeno (DBT). Uma vez estabelecidas estas condições, foi analisado o efeito do teor de V2O5 presente no catalisador e, posteriormente, o efeito do suporte catalítico. Os resultados obtidos mostraram a 70 C razão molar H2O2/Sde 16,6, razão carga/solvente igual a 1:1 e 100 mg do catalisador 15 % V2O5/SiO2, a conversão obtida foi de 95% / The need to reduce the gaseous emissions which causes serious environmental problems is a worldwide concern nowadays. Therefore, stricter laws aiming at to reduce the sulfur content in gasoline and diesel are being adopted in different countries, among them Brazil. Thus, the development of more efficient technologies to remove sulfur in these fuels has received increasing attention. These technologies include the physical extraction with a solvent, selective adsorption, microbiological reduction/oxidation processes and oxidative desulphurization (ODS). The oxidative desulfurization (ODS) converts sulfur compounds into sulfones that can be easily separated by physical processes. Therefore, the ODS has a great potential to become a process complementary to traditional hydrodesulfurization in the production of highly desulfurized fuels. In this context, this work studied the performance of V2O5 catalysts supported on alumina, silica and silica-alumina toward ODS reaction of dibenzothiophene in the presence of hydrogen peroxide as the oxidant, and acetonitrile as polar aprotic solvent. The catalysts were prepared by incipient wetness impregnation and characterized by X-ray diffraction (XRD), textural analysis, temperature programmed reduction (TPR-H2), temperature programmed desorption (TPD-NH3) and Raman spectroscopy. The effect of experimental parameters such as amount of solvent, O/S ratio and catalyst concentration were investigated, using alumina as a support, aiming at establishing the conditions that could lead to the higher conversion of dibenzothiophene (DBT). Once established these conditions, the effect of V2O5 content was investigated and then the effect of catalytic support. The results showed that at 70 C, H2O2/S molar ratio of 16.6, solvent/diesel ratio equal to 1: 1 and 100 mg of 15% V2O5/SiO2 catalyst, the conversion obtained was 95%
5

Propriétés électrochimiques et réponse structurale du polymorphe gamma'-V2O5 vis-à-vis de l'insertion du lithium et du sodium / Electrochemical properties and structural response of the gamma'-V2O5 polymorph toward lithium and sodium insertion

Safrany Renard, Marianne 14 December 2017 (has links)
La question du stockage de l’énergie est actuellement au cœur de nombreuses problématiques internationales. Le développement de systèmes de stockage tels que les batteries lithium ion (LIB) et sodium ion (SIB) fait donc l’objet aujourd’hui de nombreuses recherches. Dans ce contexte, les matériaux lamellaires présentant un espace inter-feuillet permettant une insertion d’espèces cationiques semblent idéals dans le cadre d’une utilisation comme matériau d’électrode positive pour ces systèmes LIB et SIB. Parmi ces structures le pentoxyde de vanadium, sous sa forme alpha est un composé modèle présentant de nombreux intérêts pour les batteries au lithium. Ce matériau présente en outre de nombreux polymorphes stables autorisant un large champ d’étude de ce composé.Dans cette thèse, nous nous sommes intéressés au polymorphe gamma’-V2O5 présentant une structure lamellaire à très large inter-feuillet laissant présager une insertion d’espèces cationiques facilitée et donc des performances électrochimiques accrues. Le but de cette thèse a consisté à étudier les propriétés électrochimiques et la réponse structurale de ce composé vis-à-vis de l’insertion des ions lithium et sodium.La première partie de cette thèse propose une analyse bibliographique de l’état de l’art sur les accumulateurs lithium-ion et sodium.Dans une seconde partie les données concernant l’insertion du lithium et du sodium dans le composé alpha-V2O5 sont présentées. Les propriétés électrochimiques et structurales de ce matériau d’insertion permettront de mettre en avant l’intérêt de l’utilisation du polymorphe gamma’-V2O5 comme matériau d’électrode positive pour les systèmes LIB et SIB.Une troisième partie de ce mémoire présente la synthèse et la caractérisation du polymorphe gamma’-V2O5. L’étude complète de ce système est présentée dans le cas de l’insertion du lithium avec une étude des performances électrochimiques, une étude cinétique de la réaction d’insertion réalisée par spectroscopie d’impédance complexe et la description des changements structuraux étudiés pas diffraction des rayons X et par spectroscopie Raman.Dans une quatrième partie, l’insertion électrochimique du sodium dans le polymorphe gamma’-V2O5 est étudiée en suivant la même démarche. Le mécanisme structural impliqué dans le fonctionnement électrochimique est résolu. La formation d’un bronze de vanadium au sodium jamais encore décrit, gamma-Na0,97V2O5, est révélée et la détermination de sa structure est réalisée. Les caractéristiques électrochimiques remarquables de gamma’-V2O5, et notamment sa tension élevée de 3,3V et son excellente stabilité en cyclages, permettent de situer ce composé parmi les cathodes les plus performantes pour batterie au sodium / The question of energy storage is currently at the heart of many international issues. The development of storage systems such as lithium ion (LIB) and sodium ion (SIB) batteries is therefore today the subject of many researches.In this context, layered materials having an interlayer space allowing insertion of cationic species seem ideal in the context of use as a positive electrode material for these LIB and SIB systems. Among these structures, vanadium pentoxide, in its alpha form, is a model compound with many advantages as an attractive cathode material for lithium batteries. This material also has numerous stable polymorphs allowing a wide field of study of this compound.In this thesis we were interested in the gamma'-V2O5 polymorph, which exhibits a layered structure with very large interlayer space allowing an easier insertion. Therefore, increased electrochemical performances are expected for this compound. The aim of this thesis was to study the electrochemical properties and the structural response of this compound toward the insertion of lithium and sodium ions.The first part of this thesis proposes a review of the current literature studies devoted to lithium-ion and sodium batteries.In a second part, a thorough study of the electrochemical lithium and sodium insertion in the alpha-V2O5 phase are depicted. The electrochemical and structural properties of alpha-V2O5 will make it possible to highlight the advantage of using the polymorph gamma'-V2O5 as a positive electrode material for LIB and SIB.The third part of this thesis presents the synthesis and characterization of the gamma'-V2O5 polymorph. The complete study of this system is presented in the case of the insertion of lithium with a study of electrochemical performances, a kinetic study of the insertion reaction carried out by complex impedance spectroscopy and a description of the structural changes studied by X-ray diffraction and by Raman spectroscopy.In the fourth chapter, the insertion of sodium into the polymorph gamma'-V2O5 is studied, using the same approach than that adopted in the case of lithium. The structural mechanism involved during the electrochemical process is solved. The formation of a new sodium vanadium bronze, gamma-Na0.97V2O5 , is revealed and its structural determination is carried out. Due to its remarkable electrochemical characteristics, especially its high voltage of 3,3V and excellent cycling stability, the gamma'-V2O5 oxide ranks among the most performant cathode materials for sodium batteries
6

Dessulfurização oxidativa do dibenzotiofeno catalisada por V2O5 suportado / Oxidative desulfurization of dibenzothiophene catalyzed by supported V2O5

Débora Gomes Baptista Dionizio 16 September 2014 (has links)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A necessidade de redução da emissão de poluentes, visando diminuir os sérios problemas de poluição atmosférica enfrentados atualmente, é hoje uma das principais preocupações mundiais, provocando o surgimento de leis mais rígidas, que restringem o teor de enxofre na gasolina e no diesel. Assim, o desenvolvimento de tecnologias mais eficazes na remoção de enxofre nestes combustíveis tem recebido atenção crescente. Estas tecnologias incluem a extração física com solvente, a adsorção seletiva, processos de redução/oxidação microbiológicos e a dessulfurização oxidativa (ODS). A dessulfurização oxidativa converte os compostos de enxofre em sulfonas que podem ser facilmente separadas por processos físicos. Portanto, a ODS apresenta grande potencial para tornar-se um processo complementar a processo de hidrodessulfurização tradicional na produção de combustíveis altamente dessulfurizados. Neste contexto, este trabalho visou o estudo do desempenho de catalisadores de V2O5 suportados em alumina, sílica e sílica-alumina frente à reação de ODS do dibenzotiofeno em presença do peróxido de hidrogênio, como oxidante, e da acetonitrila, como solvente polar aprótico. Os catalisadores foram preparados por impregnação ao ponto úmido e caracterizados por difração de raios-X (DRX), análise textural, redução à temperatura programada (TPR-H2), dessorção de amônia à temperatura programa (TPD-NH3) e espectroscopia Raman. O efeito de parâmetros reacionais como quantidade de solvente, relação O/S e concentração de catalisador foram investigados, utilizando a alumina como suporte, visando estabelecer as condições reacionais que levassem a maiores valores de conversão do dibenzotiofeno (DBT). Uma vez estabelecidas estas condições, foi analisado o efeito do teor de V2O5 presente no catalisador e, posteriormente, o efeito do suporte catalítico. Os resultados obtidos mostraram a 70 C razão molar H2O2/Sde 16,6, razão carga/solvente igual a 1:1 e 100 mg do catalisador 15 % V2O5/SiO2, a conversão obtida foi de 95% / The need to reduce the gaseous emissions which causes serious environmental problems is a worldwide concern nowadays. Therefore, stricter laws aiming at to reduce the sulfur content in gasoline and diesel are being adopted in different countries, among them Brazil. Thus, the development of more efficient technologies to remove sulfur in these fuels has received increasing attention. These technologies include the physical extraction with a solvent, selective adsorption, microbiological reduction/oxidation processes and oxidative desulphurization (ODS). The oxidative desulfurization (ODS) converts sulfur compounds into sulfones that can be easily separated by physical processes. Therefore, the ODS has a great potential to become a process complementary to traditional hydrodesulfurization in the production of highly desulfurized fuels. In this context, this work studied the performance of V2O5 catalysts supported on alumina, silica and silica-alumina toward ODS reaction of dibenzothiophene in the presence of hydrogen peroxide as the oxidant, and acetonitrile as polar aprotic solvent. The catalysts were prepared by incipient wetness impregnation and characterized by X-ray diffraction (XRD), textural analysis, temperature programmed reduction (TPR-H2), temperature programmed desorption (TPD-NH3) and Raman spectroscopy. The effect of experimental parameters such as amount of solvent, O/S ratio and catalyst concentration were investigated, using alumina as a support, aiming at establishing the conditions that could lead to the higher conversion of dibenzothiophene (DBT). Once established these conditions, the effect of V2O5 content was investigated and then the effect of catalytic support. The results showed that at 70 C, H2O2/S molar ratio of 16.6, solvent/diesel ratio equal to 1: 1 and 100 mg of 15% V2O5/SiO2 catalyst, the conversion obtained was 95%
7

Structural and dielectric properties of V2O5 addition on Bi5Ti3FeO15 ceramic matrix / Estudo das propriedades dielÃtricas e estruturais do Bi5Ti3FeO15 adicionado de V2O5

Francisco Andrà Andrade de Aguiar 08 January 2016 (has links)
O Bi5Ti3FeO15 foi sintetizado pelo mÃtodo de ReaÃÃo no Estado SÃlido (RES) e posteriormente adicionado de V2O5 (PentÃxido de VanÃdio) objetivando melhorar suas propriedades dielÃtricas. Para as anÃlises estruturais foram utilizadas as seguintes tÃcnicas: DifraÃÃo de Raios-X (DRX), Microscopia EletrÃnica de Varredura (MEV), Espectroscopia de DispersÃo de Energia de Raios-X (EDS), Espectroscopia Raman e Infravermelho (IV). Para o estudo das propriedades dielÃtricas do material em radiofrequÃncia e em microondas, foram empregadas, respectivamente, a Espectroscopia de ImpedÃncia (EI) e o mÃtodo de Hakki e Coleman. A tÃcnica de DRX foi utilizada para identificar a fase BFT pura, bem como as duas novas fases originadas a partir da adiÃÃo de V2O5: Bi4V1.5Fe0.5O10.5 e Bi2Ti2O7. As alteraÃÃes na morfologia dos grÃos e a resposta dielÃtrica foram atribuÃdas à presenÃa destas fases secundÃrias. Em radiofrequÃncia verificou-se que a adiÃÃo de V2O5 aumentou a permissividade dielÃtrica e reduziu os valores de tangente de perda, resultados semelhantes aos obtidos em microondas. Ressonadores DielÃtricos foram fabricados como um protÃtipo para antena monopolo. Os valores de frequÃncia de funcionamento da antena variaram entre 2,4 GHz e 3,1 GHz. Jà os valores de coeficiente de temperatura da frequÃncia ressonante (f) variaram de -330 a -192 ppm/ÂC. Assim sendo, a cerÃmica BFT adicionada de V2O5, pode ser utilizada em dispositivos de microondas, como telefones mÃveis, por exemplo. / The Bi5Ti3FeO15 (BFT) was synthesized by the solid state reaction method (SLR) and then added by V2O5 (vanadium pentoxide) to improve its dielectric properties. For the structural analyses the following technics were used: X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Raman and infrared spectroscopy. For the dielectric propeties of the material at radiofrequency and microwave ranges, impedance spectroscopy (IS) and the Hakki-Coleman methods were used respectively. The XRD technique was used to identify the BFT phase as well as the two new ones (Bi4V1.5Fe0.5O10.5 and Bi2Ti2O7). Changes in the grain morphology and the dielectric response were assigned due to the presence of these secondary phases. The V2O5 addition increased the dielectric permittivity and reduced the loss tangent values at radiofrequency range; similar results were obtained at microwave. The Dielectric resonators (DR) were fabricated as a prototype for monopole antenna. The antenna operating frequency (2.4 - 3.1 GHz) and temperature coefficient of resonance frequency (τf) (from -330 to -192 ppm/ÂC) changed as a function of V2O5 concentration in the DR. Thus, BFT ceramics added by V2O5 are good candidates to be used for microwave devices as cell mobile phones, for example.
8

Influência do hidrocloreto de polialilamina e nanopartículas de prata na eletro-inserção de íons lítio em matrizes hospedeiras de V2O5 / Poly(allylamine hydrochloride) and silver nanoparticles influence on the lithium ions electro-insertion in V2O5 host matrix.

Nelson Alexandre Galiote Silva 05 May 2011 (has links)
Materiais automontados de V2O5, polialilamina (PAH) e nanopartículas de prata (AgNP) foram preparados pelo método camada-por-camada, visando a sua aplicação em baterias de íon-lítio e dispositivos eletrocrômicos. O método adotado permitiu o crescimento linear de filmes visualmente homogêneos de V2O5, V2O5/PAH e V2O5/PAH/AgNP com 15 bicamadas, como observado a partir de microscopia eletrônica de varredura (MEV) e espectroscopia eletrônica na região do visível. De acordo com os espectros de infravermelho com transformada de Fourier (FTIR), verificou-se que a interação entre o oxigênio do grupo vanadila e o grupo amino deve ser responsável pelo crescimento destes filmes, além de permitir uma blindagem eletrostática entre os íons lítio e os sítios com maior densidade de carga negativa, aumentando a velocidade difusional e, consequentemente, aumentando a capacidade de armazenamento de energia e diminuição do tempo de resposta. Resultados eletroquímicos e espectroeletroquímicos mostraram que a presença das AgNPs estabilizadas no PAH aumentou a capacidade de carga do eletrodo, propiciando novos caminhos condutores e aumentando o número de sítios eletroativos na matriz hospedeira. Espontaneamente, novas nanoarquiteturas com interações específicas foram formadas pelo método camada-por-camada, garantindo uma maior velocidade de transporte de massa e transferência de carga em eletrodos para baterias de lítio e dispositivos eletrocrômicos. / Self-assembled Materials from V2O5, polyallylamine (PAH) and silver nanoparticles (AgNP) were prepared by layer-by-layer method, aiming at its application in lithium-ion batteries and electrochromic devices. The adopted method allowed the linear growth of visually homogeneous films from V2O5, and V2O5/PAH, V2O5/PAH/AgNP with 15 bilayers. This was observed from scanning electron microscopy (SEM) and electronic spectroscopy in the visible region. According to the Fourier transform infrared (FTIR) spectra, it was found that the interaction between vanadyl groups oxygen and the amino group should be responsible for the growth of these films. Besides, this interaction allowed an electrostatic shield between the lithium ions and the sites with higher negative charge, increasing the ionic speed and diffusion, thereby increasing energy storages capacity and response times reduction. Electrochemical and spectroelectrochemical results showed that the presence of AGNPs stabilized in PAH increased the electrodes capacity, providing new path-ways and increasing the number of electroactive sites in the host matrix. Spontaneously, new nanoarchitectures to specific interactions were formed by the layer-by-layer method, ensuring a higher rate of mass transport and charge transfer in electrodes for lithium batteries and electrochromic devices application.
9

Preparação e caracterização de pentóxido de vanádio mesoporoso e reações de intercalação / Synthesis and characterization of mesoporous vanadium pentoxide and intercalation reaction

Guerra, Elidia Maria 17 August 2007 (has links)
A obtenção de pentóxido de vanádio mesoporoso, bem como a síntese, caracterização e estudo das propriedades de novos compostos híbridos, formado a partir do xerogel de pentóxido de vanádio e do pentóxido de vanádio mesoporoso, intercalados com espécies convidadas, foram os objetivos desta tese. O interesse nestes materiais, que apresentam uma considerável gama de modificações estruturais e químicas, é devido a possibilidade de arquitetar propriedades específicas e produzir novos materiais visando aplicações em óptica, catálise, dispositivos eletrônicos e sensores. Os compostos híbridos foram obtidos mediante a reação de intercalação utilizando espécies diretivas estruturais, como cloreto de cetilpiridínio, e materiais poliméricos, como óxido de polietileno e poli o-metoxianilina, introduzidos no interior do óxido em questão. O método de síntese é simples e relativamente rápido, uma vez que os materiais são obtidos em, no máximo, 10 dias, além de não ser necessário o monitoramento durante o período de preparação e secagem. Os resultados experimentais apontaram que houve uma expansão interplanar, bem como, as propriedades eletroquímicas dos compósitos apresentaram uma maior estabilidade de após vários ciclos quando comparados ao xerogel de pentóxido de vanádio, indicando uma reação de intercalação. Uma outra etapa deste trabalho foi à obtenção de óxido de vanádio mesoporoso. A formação de mesoporos foi confirmada pelas isotermas de adsorção/desorção. Em seguida, foi realizada a reação de intercalação com a introdução de óxido de polietileno e poli o-metoxianilina. A reação de intercalação utilizando esses polímeros na matriz mesoporosa proporcionou o aumento da mobilidade de íons lítio bem como um aumento na carga total, durante a reação redox, resultando num efeito sinérgico. Neste contexto, pode-se afirmar que, o método empregado mostrou-se extremamente atrativo devido a sua simplicidade de realização, além de possibilitar a obtenção de materiais com potencial aplicação como dispositivos eletroquímicos, baterias, e sensores químicos. / Synthesis, characterization of vanadium pentoxide mesoporous and studies of properties of hybrids compound based on vanadium oxide xerogel and vanadium pentoxide mesoporous, intercalated with guest species have been the main of this thesis. The interest in those materials, that present a considerable structural and chemical modification, is due to the possibility to tailor specific properties and produce new materials to application in optic, catalysis, electronic displays and sensors. The hybrid compounds were obtained from intercalation reaction utilizing templates agent such cetylpyridinium chloride and polymerics species such polyethylene oxide and poly o-methoxyaniline into the oxide. The synthesis is simple and relatively fast, and those materials are obtained, in a maximum, 10 days, even though it is not necessary the monitoring during the preparation and dry. The experimental results show an increase of interplanar, as well as, electrochemical properties of composites presented a better stability after several cycles as compared to vanadium pentoxide xerogel, indicating an intercalation reaction. Another stage of this work was to obtain the mesoporous vanadium pentoxide. The presence of porous was confirmed by adsorption isothermal method. Afterwards, it was realized the intercalation reaction with the polyethylene oxide and poly o-methoxyaniline into the matrix. The intercalation reaction using polymers into the porous matrix resulted an increase of Li+ ions mobility as well as an increase of total charge during the redox reaction resulting a synergic effect. In this context, it can be state that, the method used showed extremely attractive due to its simple synthesis, as well as it has the possibility of obtain materials with potential application such electrochemical displays, batteries and chemical sensors.
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Effects of Fabrication Parameters on the Electrical Properties of Al/(Bi4Ti3O12+V2O5)/Ba(Zr0.1Ti0.9)O3/Si Structure for the Application on Non-volatile FeRAM Devices

Chen, Lu-nl 24 July 2006 (has links)
In this study, the electrical properties of [Al/(Bi4Ti3O12+V2O5 ) /Ba(Zr0.1Ti0.9)O3/Silicon¡AMFIS ]structure using annealed-BZT films would be improved for the nonvolatile FeRAM device applications. The radio-frequency magnetron sputtering was used to deposit BTV ferroelectric films on Mo/Ti/SiO2/Si and BZT/Si substrates, respectively, and MFMIS and MFIS structures would also be fabricated. The various sputtering parameter effects of BTV films such as the oxygen concentrations, rf power and deposition time would be discussed. Besides, the electrical and physical properties of as-deposited BZT films for (BTV/BZT/Si¡AMFIS) structure would be improved by different rapidly thermal annealing temperature. The physical characteristics of BTV films and annealed-BZT films for various sputtering parameters were obtained from the XRD pattern and SEM morphology. Besides, the memory window, dielectric constant and leakage current of MFM and MFIS structure using BTV films and annealed-BZT films would be found from the HP4284A, RT66A and HP4156C. From the experimental result obtained, the maximum dielectric constant of BTV films for 40 % oxygen concentration and 130W power were 10.79. The leakage current density was about 10-5A/cm2, as the applied electrical field of 200 kV/cm. In addition, the coercive field (Ec) and remanent polarization (2Pr) were 750 kV/cm and 12 £gC/cm2 from the P-E curves, respectively. Finally, the maximum memory window and lower leakage current density of [Al/(Bi4Ti3O12+V2O5) /Ba(Zr0.1Ti0.9)O3/Silicon¡AMFIS) structure would be found and they were 25V and 10-8A/cm2, respectively.

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