Dissertations / Theses on the topic 'CaCu3Ti4O12'

Mestrado em Ciência e Engenharia de Materiais
CaCu3Ti4O12 (CCTO) foi produzido a temperatura baixa por moagem de alta energia e o seu impacto nas propriedades eléctricas estudado. O CCTO desenvolve um mecanismo de condensador de interface interna resistiva (do inglês IBLC) devido a desvios de estequiometria da composição inicial, a temperaturas de processamento intermédias (900-1100 oC). Este projeto tem como objectivo diminuir a temperatura de calcinação e, consequentemente, a de sinterização, de forma a reter a composição estequiométrica durante o processamento do CCTO. A evolução da fase CCTO foi controlada por difração de raios-X e as amostras foram sinterizadas pelo método convencional no intervalo de temperaturas entre 700 e 1100 oC, e caraterizadas por espetroscopia de impedância em temperaturas criogénicas e acima de temperatura ambiente. As amostras sinterizadas a 1100 oC foram, em seguida, caraterizadas por SEM e EDS. Os resultados mostram que a técnica de moagem de alta energia permite produzir pós de CCTO a temperaturas mais baixas, 700 oC, quando comparada com a síntese convencional por reação no estado sólido (950.-.1100 oC). As medidas por espetroscopia de impedância mostram que as amostras sinterizadas a 700 oC são constituídas por grãos resistivos com resistividade > 1 MΩ cm a 523 K e, portanto, a composição estequiométrica permanece inalterada e o mecanismo de IBLC não está presente. A densidade relativa é, contudo, bastante baixa, 57 %. Com o aumento da temperatura de sinterização, os grãos começam a tornar-se semicondutores e o mecanismo IBLC começa a desenvolver-se, acompanhado por um decréscimo acentuado da resistividade do grão em pelo menos seis ordens de grandeza. Para temperaturas de sinterização intermédias, 800.-.900 oC, os grãos são constituídos por uma fase semicondutora rodeada por uma fase resistiva. Para temperaturas de sinterização de 1000 oC, os grãos são semicondutores com resistividade ~ 40 Ω cm e fronteiras de grão ~ 530 Ω cm a 523 K. As amostras sinterizadas a 1100 oC são constituídas por grãos semicondutores e fronteiras de grão resistivos com resistividade ~ 65 kΩ cm a 523 K. Esta diferença de resistividades parece estar na origem da elevada permitividade dielétrica no intervalo de radiofrequências. A análise por EDS revela que a amostra sinterizada a 1100 oC é deficiente em cobre, o que contribui para o aumento da condutividade do grão. A transformação do grão resistivo em semicondutor parece estar, portanto, associada à difusão e eventual volatilização de cobre a temperaturas de processamento elevadas
CaCu3Ti4O12 (CCTO) powders were produced at low temperatures by high-energy ball milling and its impact on the electrical properties of CCTO ceramics carried out. CCTO ceramics develop an internal barrier layer capacitance (IBLC) mechanism due to small changes in stoichiometry, which seems to start at intermediate processing temperatures (900.-.1100.oC). This project aims to decrease the calcination and sintering temperatures to retain the stoichiometric composition during processing of CCTO ceramics. The evolution of the CCTO phase was evaluated by X-ray diffraction and ceramics were prepared by conventional sintering at temperatures between 700 and 1100 oC. The samples were characterised by impedance spectroscopy at subambient and high temperatures. Ceramics sintered at 1100 oC were characterised by SEM and EDS. The results show that high-energy ball milling permits the production of CCTO powder at lower temperature, 700.oC, compared to conventional solid state reaction (950.-.1100.oC). Impedance spectroscopy measurements show that ceramics sintered at a temperature of 700.oC, the stoichiometric composition of CCTO is retained and consists of insulating grains with a resistivity > 1 MΩ cm at 523 K. The relative density is, however, rather low, 57 %, and the IBLC mechanism is not present in this sample as usually observed for CCTO ceramics. When the sintering temperature increases, the insulating grains start to transform into semiconducting and the IBLC mechanism starts to appear, accompanied by a significant drop on the resistivity by at least six orders of magnitude for ceramics sintered at 1000 oC. At intermediate sintering temperatures, 800 - 900.oC, the grains are electrically heterogeneous containing both insulating and semiconducting phases. When samples are sintered at 1000 oC, the grains are totally semiconducting with resistivity of ~ 40 Ω cm and grain boundary resistivity of ~ 530.Ω.cm at 523 K. Ceramics sintered at 1100 oC exhibit semiconducting grains surrounded by insulating grain boundary with resistivity of ~ 65 kΩ cm at 523 K, and this seems to be responsible for the high effective permittivity at radio frequencies for dense ceramics. The EDS analysis shows CCTO ceramics sintered at 1100 oC to be Cu-deficient and it contributes to the increase of the bulk conductivity. The transformation of the resistive into semiconducting grains and the evolution of the IBLC mechanism may be, therefore, linked to the diffusion and eventual volatilisation of copper at elevated processing temperatures.

Neste trabalho pós de CaCu3Ti4O12 foram preparados por reação em estado sólido e por técnicas de solução: complexação de cátions e coprecipitação dos oxalatos. Foram realizados estudos de formação de fase, densificação e propriedades dielétricas das cerâmicas sinterizadas. Para efeito comparativo, ta is propriedades foram determinadas em amostras puras e contendo dissilicato de lítio (LSO) e fluoreto de lítio (LiF) como aditivos de sinterização. O principal objetivo foi verificar o efeito do uso dos diferentes aditivos de sinterização na microestrutura, densificação e propriedades dielétricas do CCTO. Os principais resultados revelaram que pós preparados por técnicas de solução apresentam fase única após calcinação em condições selecionadas. Foi verificado que os aditivos influenciam na densificação, possibilitando obter cerâmicas com 95% da densidade teórica do CCTO a 1025°C. As amostras preparadas por diferentes técnicas apresentam propriedades similares, com exceção das características microestruturais. A permissividade elétrica determinada à temperatura ambiente é da ordem de 104 independentemente do método de síntese. As menores perdas dielétricas foram obtidas para amostras contendo LiF como aditivo de sinterização.
In this work the effects of the method of synthesis and sintering additives on the microstructure and dielectric properties of CCTO were investigated. Powder mixtures were prepared by the cation complexation and coprecipitation methods, and by mixing of the starting oxides, for comparison purposes. Lithium dissilicate (LSO) and lithium fluoride (LiF) were used as sintering aids. The main results revealed that powders prepared by solution techniques have single phase after calcination at selected conditions. The additives were found to influence the densification allowing for obtaining high relative density (≥ 95%) at 1025ºC. Specimens prepared by different methods show similar properties except on microstructure features. The electric permittivity is of the order of 104 for all investigated specimens independent on the method of synthesis. The dielectric loss is found to be lower for specimens prepared with LiF as sintering aid.

Les oxydes de type pérovskites présentent différentes propriétés selon leur structure et leur composition chimique. Les principales pérovskites étudiées, BaTiO3 et YBa2Cu3O7, possèdent d’intéressantes propriétés ferroélectriques et supraconductrices. Une des limitations de ce type d’oxydes est la transition de phase à haute température qui peut modifier leurs propriétés. Le matériau CaCu3Ti4O12 (CCTO) est un oxyde connu comme double perovskite (ABO3) à structure cubique, qui a été étudié ces dernières années en tant que matériau diélectrique de permittivité élevée. De plus, CCTO subit une transition magnétique à antiferromagnétique au-dessous de la température de Néel (TN=25K). Les propriétés du matériau CCTO sont fortement dépendantes de sa structure et offrent des possibilités d’applications photoélectrochimiques. D'un autre côté, les nanofeuillets de nitrure de bore (h-BN) et d’oxyde de graphène (GO) sont des matériaux 2D présentant des propriétés très intéressantes.Dans le cadre de ce travail, des matériaux composites à base de CCTO et de nanofeuillets de nitrure de bore et d’oxyde de graphène ont été synthétisés et étudiés. Les céramiques composites CCTO/GO et CCTO/h-BN ont été synthétisées par réaction solide-solide. Les différentes propriétés photoélectrochimiques, diélectriques, et magnétiques ont été caractérisées. L’addition de 3% de h-BN aboutit à l’incorporation des atomes du bore et d’azote dans le réseau cristallin du CCTO et forme les liaisons Ti-B-O et Ti-N-O, et génère des lacunes d’oxygène à la surface, ce qui améliore la génération de porteurs de charges. La génération de porteurs de charges est augmentée en 50% par rapport au CCTO pur, après l’addition de 3% de GO, due à l’oxydation de GO à haute température qui réduit Ti4+ et Cu2+ en site actifs Ti3+ et Cu+ respectivement. Les propriétés magnétiques du CCTO avec 6% de nanofeuillets ont été étudiées, et ont montré que la température Néel n’était pas modifiée. Enfin, un polissage est effectué à la surface des céramiques pour étudier leurs propriétés diélectriques. Les résultats montrent des valeurs de permittivité plus basse que celles décrites dans la littérature. En conclusion, ces travaux ont démontré que l’incorporation des nanofeuillets 2D n’affecte pas les propriétés diélectriques et magnétiques, mais améliore considérablement les propriétés photoélectrochimiques du CCTO
Perovskite oxides exhibit a large variety of properties because of their structures and chemical compositions. Well known properties of the perovskite oxides are Ferroelectricity in BaTiO3-based oxides and superconductivity in YBa2Cu3O7. The major limit of these compounds is their phase transitions at high temperature, which lead to modify the perovskite properties. CaCu3Ti4O12 (CCTO) exhibit a cubic structure stable at high temperature, it is a double-perovskite (ABO3). CCTO was known as high dielectric material, and can play a key role in photoelectrochemical activity due to its structure. In addition, CCTO can occur a phase transition into the antiferromagnetically ordered phase below Neel temperature TN = 25 K. On the other hand, 2D nanomaterials including graphene oxide (GO) and hexagonal boron nitrides (h-BN) were widely used due their exceptional properties.The aim of this thesis is to investigate the photoelectrochemical, dielectric, and magnetic properties of CCTO based composites. Composites made of CCTO/GO and CCTO/h-BN ceramics were fabricated by solid-state reaction. With the addition of 2D nanosheets materials, the photoelectrochemical performance is enhanced by increasing the generation of photocurrent. CCTO with 3%wt of h-BN showed the insertion of bore (B) and nitrogen (N) into CCTO lattice, leading to Ti-B-O, Ti-N-O bonds and oxygen vacancies on the surface which reduce the bang gap energy and increase the density of generated photocurrent. With 3% of GO, Ti4+ and Cu2+ were reduced to active species Ti3+ and Cu+ respectively and oxygen vacancies were generated at the surface for charge neutralization, leading to generate photocurrent density 50% higher than pure phase of CCTO. In order to investigate 2D nanomaterials effects on magnetic properties of composites, CCTO with 6%wt of nanosheets was prepared and have shown no significant changes in Neel temperature. Finally in the last section, all composites were surface polished to investigate their dielectric properties, measurements showed a low permittivity in comparison to the literature. In conclusion, this work has shown that 2D nanosheets materials incorporation does not affect dielectric and magnetic properties, but enhance strongly the photoelectrochemical behavior of CCTO

A promising strategy to mitigate both the energy crisis and global warming is the development of solar fuels and chemicals using as feedstock CO2 in combination with simple molecules such as water. This process stores the solar energy into chemical bonds, leading to a carbon-neutral approach of fuels and chemicals production. Aim of this thesis was the synthesis and characterization of CaCu3Ti4O12 (CCTO)- based compounds to be used as visible light photocatalyst for CO2 to chemical conversion. Different compositions were produced doping CCTO with increasing concentration of iron into the perovskite’s A site in order to identify the materials with the highest photo- and photoelectrocatalytic properties. The most promising compositions were used to produce photoelectrodes by screen printing that were characterized by linear and cyclic voltammetry, impedance spectroscopy and Mott-Schottky analysis to evaluate the electrical conductivity and calculate the flat band potential and the number of charge carriers in the samples. The photoelectrodes were then tested in a photoelectrochemical (PEC) cell for the conversion of CO2 into fuel and chemicals. The results obtained confirm that CCTO-based materials can be considered promising materials for carbon dioxide photo-electrochemical reduction.

Structural studies with CaCu3Ti4O12 (CCTO) are made since the 1970s, however investigations about their electrical properties only started recently. At 2000, it was reported a high permittivity of ~ 12000 (at 1 KHz) in ceramics of this material which remained constant between the room temperature to ~ 200 °C, and whose physical explanations be still controversial in the scientific society. High dielectric constants allow smaller capacitive components, enabling the size reduction of the electronic devices. In this way, CCTO has attracted the interest of many researchers as technological as scientific point of view. One of the main problem that limit its immediate application as dielectric in ceramic capacitors is its high dielectric loss (~ 0,15) near at room temperature. On the other hand, this material has been prepared by several researchers mainly by the solid state reaction method, in the temperature range of 1000 °C to 1050 °C, with thermal treatment up to 48 h. As result, some secondary phases have be found as in the calcined powders as in the sintered ceramics. Thus, other synthesis methods have been proposed and tested in the last years. In this work, we have studied the CCTO synthesis by a route based on Pechini s method and its sintering using a new method, in which a CO2 laser is used as the main heating source. Besides, the dielectric properties of CCTO ceramics were investigated in order to verify the influence of this sintering process on the ceramic properties as well as onto the understanding of the involved physical mechanisms. The laser sintered ceramics presented high relative density (95 ± 1%), with homogeneous microstructure and dielectric constant at about 2000 with low dielectric loss (0,06) at 1 kHz, when sintered at 1,3 W/mm2. The dielectric loss value obtained in this work is among the lowest ever recorded. Based on our results was also proposed a mechanism to aid in the understanding of the giant dielectric constant in CCTO. Finally, we believe that laser sintering can be an important tool for the optimization of the dielectric properties of CCTO ceramics and consequently future applications in the capacitors and electronic devices industry, whose worldwide consumption is increasing.
Estudos estruturais com o CaCu3Ti4O12 (CCTO) são feitos desde os anos 1970, contudo investigações acerca de suas propriedades elétricas somente se iniciaram recentemente. Em 2000, foi reportado uma alta permissividade de ~ 12000 (a 1 kHz) em cerâmicas deste material, que permanecia constante da temperatura ambiente a ~ 200 °C, cujas explicações físicas ainda são bem controversas na comunidade científica. Constantes dielétricas altas permitem menores componentes capacitivos, oferecendo assim a oportunidade de diminuir o tamanho de dispositivos eletrônicos. Desta forma, o CCTO tem atraído muito o interesse de pesquisadores, tanto do ponto de vista tecnológico quanto científico. Um dos principais problemas que limitam sua imediata aplicação como dielétrico em capacitores cerâmicos é a sua alta perda dielétrica (~ 0,15) próximo à temperatura ambiente. Por outro lado, este material tem sido preparado por diversos pesquisadores principalmente pelo método da reação de estado sólido, no intervalo de temperatura de 1000 °C a 1100 °C, com tratamentos térmicos de até 48 h. Como resultado, algumas fases secundárias têm sido encontradas tanto no pó calcinado quanto na cerâmica sinterizada. Dessa forma, outros métodos de síntese vêm sendo procurados e testados nos últimos anos. Neste trabalho, estudamos a síntese do CCTO por uma rota baseada no método Pechini e sua sinterização usando um novo método, no qual um laser de CO2 é usado como principal fonte de aquecimento. Além disso, estudamos as propriedades dielétricas das cerâmicas de CCTO, a fim de verificar a influência deste novo processo de sinterização em suas propriedades bem como no entendimento dos mecanismos físicos envolvidos. As cerâmicas sinterizadas a laser apresentaram alta densidade relativa (95 ± 1%), com microestrutura homogênea e constante dielétrica em torno de 2000 e baixa perda dielétrica (0,06) a 1 kHz, quando sinterizadas a 1,3 W/mm2. O valor de perda dielétrica obtida neste trabalho está entre os mais baixos já registrados. Baseando-se em nossos resultados também foi proposto um mecanismo para auxiliar no entendimento da constante dielétrica gigante no CCTO. Finalmente, acreditamos que a sinterização a laser pode ser uma importante ferramenta para a otimização das propriedades dielétricas de cerâmicas de CCTO e consequentemente futuras aplicações na indústria de capacitores e dispositivos eletrônicos, cujo consumo mundial é cada vez maior.

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Neste trabalho pastilhas cerâmicas de CaCu3Ti4O12 (CCTO) foram produzidas pelo método de reação por estado sólido onde estudos por difração de raios-X mostraram que as amostras policristalinas são monofásicas dependendo da pressão parcial de oxigênio. Estudos por microscopia eletrônica de varredura e fotoluminiscência indicam que o processo de crescimento de grão e densificação das amostras e a formação de vacâncias de oxigênio estão diretamente relacionados a concentração de oxigênio durante o processo de sinterização. As amostras foram caracterizadas por medidas elétricas dc em função da temperatura, que associada a teoria de semicondutores, provaram que as barreiras de potencial no CCTO são mais influenciadas pela temperatura do que pelo campo elétrico, ou seja, são barreiras do tipo Schottky. Um modelo de barreira e os mecanismos de formação foram propostos para descrever a formação da barreira de potencial no CCTO. Medidas de corrente-tensão cíclicas mostraram que o efeito de comutação resistiva no CCTO está diretamente relacionado a efeitos de contorno de grão e efeito Joule. As propriedades de transporte elétrico em filmes finos de CCTO foram investigadas para os efeitos de comutação resistiva, retificação elétrica e aplicação em sensores de gás. Filmes monofásicos foram produzidos pelo Método dos Precursores Poliméricos (MPP) em diferentes tipos de substratos. Filmes produzidos em substratos de LNO/Si apresentam curvas de corrente-tensão simétricas, indicando contatos ôhmicos, enquanto os filmes depositados sobre substratos de Pt/Si têm um comportamento altamente assimétrico nestas curvas, o qual está relacionada com a formação de um junção metal-semicondutor na interface CCTO/Pt. Os resultados indicam que a formação deste tipo de contato reforça o efeito de comutação resistiva neste material...
CaCu3Ti4O12 (CCTO) pellets were produced by solid state reaction method and X-ray diffractograms showed that single phase polycrystalline samples were obtained. Studies by scanning electron microscopy and photoluminescence indicate that the process of growth and densification of the samples and formation of oxygen vacancies, respectively, are directly related to oxygen concentration during sinterization process. The samples were electrically characterized by dc measurements a function of temperature, which associated to semiconductor theory, showed that CCTO barriers are more influenced by temperature than by electric filed, i.e., Schottky barriers. A model and the mechanism for barrier formation have been proposed to describe the CCTO potential barrier. Electric transport properties of CaCu3Ti4O12 (CCTO) thin films were investigated for resistive switching, rectifying and gas sensor applications. Single phase CCTO thin films were produced by Polymeric Precursor Method (PPM) on different substrates. Cyclic current-voltage measurements showed that resistive switching effects in CCTO is directly related to the grain boundary and Joule effects. Films produced on LNO/Si substrates have symmetrical non-ohmic current voltage characteristics, forming ohmic contact, while films deposited on Pt/Si substrates have a highly asymmetrical non-ohmic behavior which is related to a metal-semiconductor (MS) junction formed at the CCTO/Pt interface. Results confirm that CCTO has a resistive switching response which is enhanced by Schottky contacts. Sensor response tests revealed that CCTO films are sensitive to oxygen gas and exhibit n-type conductivity. These results demonstrate the versatility of CCTO thin film prepared by the PPM method for gas atmosphere or bias dependent resistance applications depending n filme configuration

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O Programa de Pós-Graduação em Ciência e Tecnologia de Materiais, PosMat, tem caráter institucional e integra as atividades de pesquisa em materiais de diversos campi da Unesp
Resumo: Neste trabalho pastilhas cerâmicas de CaCu3Ti4O12 (CCTO) foram produzidas pelo método de reação por estado sólido onde estudos por difração de raios-X mostraram que as amostras policristalinas são monofásicas dependendo da pressão parcial de oxigênio. Estudos por microscopia eletrônica de varredura e fotoluminiscência indicam que o processo de crescimento de grão e densificação das amostras e a formação de vacâncias de oxigênio estão diretamente relacionados a concentração de oxigênio durante o processo de sinterização. As amostras foram caracterizadas por medidas elétricas dc em função da temperatura, que associada a teoria de semicondutores, provaram que as barreiras de potencial no CCTO são mais influenciadas pela temperatura do que pelo campo elétrico, ou seja, são barreiras do tipo Schottky. Um modelo de barreira e os mecanismos de formação foram propostos para descrever a formação da barreira de potencial no CCTO. Medidas de corrente-tensão cíclicas mostraram que o efeito de comutação resistiva no CCTO está diretamente relacionado a efeitos de contorno de grão e efeito Joule. As propriedades de transporte elétrico em filmes finos de CCTO foram investigadas para os efeitos de comutação resistiva, retificação elétrica e aplicação em sensores de gás. Filmes monofásicos foram produzidos pelo Método dos Precursores Poliméricos (MPP) em diferentes tipos de substratos. Filmes produzidos em substratos de LNO/Si apresentam curvas de corrente-tensão simétricas, indicando contatos ôhmicos, enquanto os filmes depositados sobre substratos de Pt/Si têm um comportamento altamente assimétrico nestas curvas, o qual está relacionada com a formação de um junção metal-semicondutor na interface CCTO/Pt. Os resultados indicam que a formação deste tipo de contato reforça o efeito de comutação resistiva neste material... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: CaCu3Ti4O12 (CCTO) pellets were produced by solid state reaction method and X-ray diffractograms showed that single phase polycrystalline samples were obtained. Studies by scanning electron microscopy and photoluminescence indicate that the process of growth and densification of the samples and formation of oxygen vacancies, respectively, are directly related to oxygen concentration during sinterization process. The samples were electrically characterized by dc measurements a function of temperature, which associated to semiconductor theory, showed that CCTO barriers are more influenced by temperature than by electric filed, i.e., Schottky barriers. A model and the mechanism for barrier formation have been proposed to describe the CCTO potential barrier. Electric transport properties of CaCu3Ti4O12 (CCTO) thin films were investigated for resistive switching, rectifying and gas sensor applications. Single phase CCTO thin films were produced by Polymeric Precursor Method (PPM) on different substrates. Cyclic current-voltage measurements showed that resistive switching effects in CCTO is directly related to the grain boundary and Joule effects. Films produced on LNO/Si substrates have symmetrical non-ohmic current voltage characteristics, forming ohmic contact, while films deposited on Pt/Si substrates have a highly asymmetrical non-ohmic behavior which is related to a metal-semiconductor (MS) junction formed at the CCTO/Pt interface. Results confirm that CCTO has a resistive switching response which is enhanced by Schottky contacts. Sensor response tests revealed that CCTO films are sensitive to oxygen gas and exhibit n-type conductivity. These results demonstrate the versatility of CCTO thin film prepared by the PPM method for gas atmosphere or bias dependent resistance applications depending n filme configuration
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A miniaturização de dispositivos eletrônicos mais rápidos e eficientes tem sido um desafio. para o desenvolvimento de novos dispositivos eletroeletrônicos com isso o estudo de. cerâmicas multifuncionais vem aumentando. A descoberta da permissividade dielétrica (). gigante de aproximadamente 105 e o coeficiente não linear (α) no CaCu3Ti4O12 (CCTO). despertou grande interesse por oferecer a oportunidade de reduzir o tamanho e otimizar as. propriedades nos dispositivos eletrônicos. No presente trabalho propôs analisar e estudar as. propriedades estruturais, microestruturais e elétricas do titanato de cobre e cálcio dopado com. molibdênio (1,00%; 2,00%; 3,00%; 4,00% e 5,00% em mol) e nióbio (1,00%; 2,00%; 3,00%;. 4,00% e 5,00% em mol) no sítio B. O processo de síntese adotado para a obtenção das. cerâmicas foi o “método tradicional de mistura de óxidos” ou reação no estado sólido, visando. à obtenção de produtos com microestrutura homogênea. Os pós foram termicamente avaliados. pela análise termogravimétrica (TG), análise térmica diferencial (DTA) e dilatometria.. Estruturalmente, os pós foram caracterizados por difração de raios X (DRX), espectroscopia. de espalhamento Raman e espectroscopia de absorção na região de infravermelho por. transformada de Fourier (FT-IR). A forma, o tamanho dos grãos e os contornos de grão foram. observados por intermédio da microscopia eletrônica de varredura (MEV). As propriedades. óticas foram investigadas por espectroscopia ótica nas regiões do ultravioleta e visível (UVVis). Os padrões de DRX indicaram a formação de soluções sólidas homogênea com estrutura. perovskita, pertencentes ao grupo espacial Im3 para todas as concentrações de Nb calcinada a. 950°C avaliadas e apenas para a concentração de 1% de Mo calcinada a 850°C. Os ajustes. teóricos dos espectros Raman indicaram a formação de fase secundária para todas as. concentrações e temperatura, mostrando que a formação da solução sólida homogênea. ocorreu apenas em longo alcance. As imagens de microscopia indicaram que os dopantes. diminuem o tamanho do grão e alteram a sua morfologia em que o nióbio deixa os grãos. hexagonais e o molibdênio os grãos esféricos. Por último, foram avaliadas as propriedades. elétricas por medidas de tensão – corrente e espectroscopia de impedância. Pôde-se observar. que as cerâmicas dopadas com Mo modificou as propriedades não-ôhmica do CCTO, não. sendo possível verificar uma possível aplicação em dispositivos varistores devido ao alto. campo necessário para a ruptura da cerâmica. Já as cerâmicas dopadas com nióbio. apresentaram características não lineares com um decréscimo da tensão de ruptura com o. aumento da concentração do dopante indicando sua aplicação como dispositivo de proteção. elétrica de baixa tensão “varistor”

Les céramiques massives issues de poudres de CaCu3Ti4O12 (CCTO) élaborées par co-précipitation suivie d'un traitement de calcination présentent des permittivités relatives colossales (150 000 à 1 kHz, Tamb), qui dépendent du taux de phase additionnelle CuO. L'étude confirme que le modèle de barrière interne est à l'origine de ces permittivités relatives. Par ailleurs, les caractérisations en tension et en impédance ont permis d'établir un modèle comportemental grâce à un circuit électrique équivalent facilement utilisable lors de simulations. Une étude originale a été menée sur des couches de CCTO mises en forme par coulage en bandes. Ces couches présentent des permittivités relatives très élevées (47 000 à 1 kHz, Tamb) pour les épaisseurs supérieures ou égales à 40 µm. Une chute brutale de la permittivité relative est observée pour les épaisseurs inférieures à 40 µm, et est liée au nombre insuffisant de barrières internes (joints de grains) électriquement actives. Des condensateurs céramiques multicouches présentant des structures internes et des propriétés électriques reproductibles ont été élaborés. Les valeurs de capacité ont été considérablement augmentées (jusqu'à 1,4 µF à 1 kHz, Tamb) et les valeurs de résistance série fortement diminuées (jusqu'à 0,3 O) par rapport aux céramiques massives. Concernant la tenue en tension, il est primordial de prendre en compte le comportement non linéaire du courant avec la tension, caractéristique de CCTO. La comparaison avec des diélectriques usuels (type Z5U) a permis de montrer que les composants élaborés présentent de meilleures caractéristiques en température et en vieillissement
Massive ceramics prepared from CaCu3Ti4O12 (CCTO) powders obtained by coprecipitation method and a calcination show colossal relative permittivities (150 000 at 1 kHz, RT), thanks to the control of additional CuO phase. The study has confirmed that the observed properties can be explained by the internal barrier model. Furthermore, the voltage and impedance characterizations allowed us to create a behavioral model with an equivalent electric circuit readily usable in simulations. An original study was conducted on CCTO films shaped by tape casting method. The films show high relative permittivity values (47 000 at 1 kHz, RT) for thicknesses greater than 40 µm. Below 40 µm, a sharp drop of the relative permittivity is observed, due to an insufficient number of internal barriers (grain boundaries) electrically active. Multilayer ceramic capacitors with reproducible internal structures and electrical properties were developed. The capacity values were significantly increased (1. 4 µF at 1 kHz, RT) and equivalent serial resistances were significantly decreased (0. 3 O), compared to massive ceramics. Regarding the tension strength, the nonlinear current-voltage behavior is an interesting characteristic of CCTO. The comparison with usual dielectrics (Z5U) has shown that the as-developed components exhibit higher temperature and aging characteristics

L’obiettivo di questo lavoro di Tesi è la sintesi e la caratterizzazione di materiali ceramici per la produzione di solar fuels per mezzo della riduzione foto-indotta della CO2 in cella foto-elettrochimica (PEC). La produzione di solar fuels non è solo importante come tecnologia potenzialmente in grado ridurre la quantità di CO2 in atmosfera derivante dall’utilizzo di combustibili fossili, ma anche come possibile mezzo di immagazzinamento di energia. Per questo scopo, è stata studiata la perovskite doppia calcio rame titanato (CCTO), avente formula chimica CaCu3Ti4O12 e sui suoi derivati dopati Fe(III), sia sul sito occupato dal Cu(II), che sul sito occupato dal Ti(IV), per ottenere, rispettivamente CaCu3–xFexTi4O12 e CaCu3Ti4–xFexO12 (x = 0.015, 0.03, 0.06, 0.1). Sono stati confrontati due metodi di sintesi valutando purezza, morfologia e area superficiale delle polveri ottenute, tramite XRD, SEM e BET, e valutandone le proprietà ottiche e fotocatalitiche in termini di degradazione della Rodamina B. Il metodo sol-gel è risultato essere il migliore per tutti i sistemi considerati. I campioni con le proprietà migliori sono stati poi utilizzati per costruire elettrodi tramite due differenti metodi: deposizione manuale e serigrafia. Le proprietà dei differenti elettrodi sono state valutate tramite voltammetria ciclica ed impedenza, tenendo principalmente conto della loro capacità di assorbire la luce. Gli elettrodi migliori preparati tramite serigrafia sono stati poi caratterizzati tramite analisi Mott-Schottky, per determinarne le proprietà elettroniche, ed infine testati in cella PEC, sia in condizioni di buio sia sotto illuminazione, per valutarne le prestazioni sia nell’ossidazione dell’acqua che nella riduzione di CO2.

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Cerâmicas à base de CaCu3Ti4O12 (CCTO) com estrutura perovskita ABO3 geraram grande interesse científico devido à descoberta da constante dielétrica (κ) gigante, propriedade não ôhmica elevada e propriedade fotoluminescente. Neste trabalho foram preparadas cerâmicas policristalinas na forma de pó com a seguinte composição: Ca1-xSrxCu3Ti4O12 (0,0 ≤ x ≤ 1,0) na qual o Ca2+ (sitio A) foi gradativamente substituído pelo cátion Sr2+. Foram analisados os efeitos desta substituição gradativa nas propriedades estruturais e microestruturais dos pós policristalinos. Mediante técnicas de análise termogravimétrica dos pós, produzidos por reação do estado sólido, determinou a temperatura de calcinação a 950ºC. Analisando as fases presentes no material por meio da técnica de difratometria raios X observa-se que a estrutura cristalina formada é do tipo perovskita. Ao realizar os estudos semi-quantitativos, mediante microscopia eletrônica de varredura com detector de energia dispersiva, se obteve a morfologia e composição química dos pós cerâmicos. Por meio das técnicas de espectroscopia (de infravermelho, de absorção ultravioleta-visível e de fotoluminescência) foram obtidos os valores 548 cm-1, 500 cm-1 e 415 cm-1, para os módulos vibracionais das ligações O-Ti-O, o band gap de 2,85 eV para as amostras estudadas e determinou-se as propriedades ópticas da cerâmica policristalina na forma de pó.
Ceramics made of CaCu3Ti4O12 (CCTO) create great scientific interest after the discovery of its giant dielectric constant (κ), the high non-ohmic property and photolumenescence. In this study were prepared polycrystalline ceramics in the form of powder with the following composition: Ca1-xSrxCu3Ti4O12 (0.0 ≤ x ≤ 1.0), in which Ca2+ (site A) was gradually replaced by a cation Sr2+. The effects of this graduated replacement were analyzed in the structural and microstructure properties of polycrystalline powders. By the thermogravimetric analysis of the powders, produced by solid state reaction, determined the calcination temperature at 1223K. Analyzing the phases present in the material by the diffraction technique of X-rays its observed that the crystal structure formed is perovskite. When conducting semi-quantitative studies, by the scanning electron microscope with energy dispersive spectroscopy, it was obtained the morphology and chemical composition of the ceramics powders. By the techniques of spectroscopy (infrared, ultraviolet-visible absorption and photoluminescence) were obtained the values 548 cm-1, 500 cm-1 and 415 cm-1, for the vibrational modules of the bonding O-Ti-O, the band gap of 2,85 eV for the studied samples and the optical properties of the powder polycrystalline ceramics were determined.

L'oxyde CaCu3Ti4O12 (CCTO) présente une permittivité élevée (~ 105) dans une large gamme de température (100-600K) et de fréquence (10HZ-1MHz). La première partie de cette étude est une tentative de dépôt de condensateurs "tout oxyde" à base de CCTO par ablation laser. Des fims épitaxiés de CCTO sur monocristal LaA1O3 (001) ont été obtenus après optimisation du frittage des cibles. LaSrNiO4 (LSNO) a servi d'électrode pour des condensateurs LSNO/CCTO/LSNO/LAO, structurés in situ par "shadow-masking". Afin de réduire la diffusion du lanthane et de cuivre et d'améliorer la qualité des interfaces avec l'électrode, une nouvelle électrode CaCu3Ru4O12 isostructural de CCTO a été développée. En parallèle, CCTO sous forme de poudre pure et dopée et de film a été étudié par RPE. Les résultats originaux sont d'importance pour la compréhension des mécanismes à l'origine des propriétés exceptionnelles de CCTO
The oxide CaCu3Ti4O12 (CCTO) shows a very high permittivity (~ 105) in a large range of temperature (100-60K) and frequencies (10Hz-1MHz). A part of this study is an atttempt to deposit "all oxide" capacitors based on CCTO using the laser on CCTO using the laser ablation technique. At first, epitaxial films of CCTO were deposited on single crystal LaA1O3(100) (LAO) after optimisation of the target sintering. Capacitors LSNO/CCTO/LSNO/LAO with LaSrNiO4 (LSNO) as electrodes were then structured in-situ by shadow-masking. In an attempt to reduce the diffusion of La and Cu and to improve the quality interface with electrode, LSNO was replaced by CaCu3Ru4O12 which was isostructural of CCTO. In a second part, CCTO in the form of pure and doped powder and thin film was studied by electron spin resonance. New results are important to understand the mechanisms giving rise to the high permittivity value

À l’heure où la miniaturisation des composants électroniques devient un enjeu majeur dans de nombreux secteurs d’activités (automobile, aérospatial, informatique…), le développement de nouvelles familles de matériaux présentant une constante diélectrique élevée et de faibles pertes diélectriques constitue, aujourd’hui encore, un axe de recherche privilégié. C’est le cas de CaCu3Ti4O12, matériau très étudié depuis les années 2000, notamment grâce à sa permittivité relative "exceptionnelle". Les travaux présentés dans cette thèse proposent une étude originale de la synthèse et du frittage de CaCu3Ti4O12 par des procédés non-conventionnels ainsi que sa caractérisation structurale, microstructurale et physique.La première étude porte sur la synthèse conventionnelle et micro-ondes de CaCu3Ti4O12. L’intérêt du chauffage micro-ondes est d’exploiter le couplage micro-ondes/propriétés diélectriques afin de permettre une synthèse rapide de la phase tout en contrôlant sa granulométrie. Par la suite, l’étude s’est consacrée à la compréhension approfondie du frittage naturel de CaCu3Ti4O12. La densification est régie jusqu’à 80% de densité par de la diffusion aux joints de grains. Il s’ensuit au cours du processus à haute température (>1000°C) l’apparition d’une phase liquide entraînant un grossissement granulaire anormal. Le recours à différentes techniques de frittage (atmosphère contrôlée, sous charge par Spark Plasma Sintering ou forgeage) a été employé pour maîtriser la microstructure de CaCu3Ti4O12. En parallèle de cette étude, une attention toute particulière a été portée sur la caractérisation nanostructurale des joints de grains. Pour la première fois, l’analyse fine réalisée en microscopie électronique en transmission révèle la nature exacte de l’ensemble des phases riches en cuivre qui ségrégent aux joints de grains de CaCu3Ti4O12. Enfin, les caractérisations structurales, microstructurales et physiques réalisées sur l’ensemble des céramiques polycristallines et monocristaux permettent d’apporter de nouveaux arguments dans la compréhension des propriétés diélectriques de CaCu3Ti4O12
As the miniaturization of electronic components is becoming a major issue in many business sectors (automotive, aerospace, computer sciences…), the development of new families of materials with a high dielectric constant and low dielectric losses is still a priority line of research. This is the case of CaCu3Ti4O12. This material has been studied extensively since 2000 thanks to its “exceptional” relative permittivity. The work presented in this thesis proposes an original study of the synthesis and sintering of CaCu3Ti4O12 by non-conventional processes and its structural, microstructural and physical characterization.The first study concerns the conventional and microwave synthesis of CaCu3Ti4O12. The interest of microwave heating is the good coupling between microwaves and the dielectric properties of the material. This allows a rapid synthesis of CaCu3Ti4O12 and the control of its particle size. Subsequently, the study focused on a thorough analysis of the natural sintering of this ceramic. Densification is controlled up to 80% of relative density by grain-boundary diffusion. At higher temperature, a liquid phase occurs during the sintering, resulting in abnormal grain growth. Various sintering techniques (controlled atmosphere, SPS, forging) were used to control the microstructure of CaCu3Ti4O12. In the meantime, particular attention was paid to the nanostructural characterization of grain boundaries. For the first time, the transmission electron microscopy analysis reveals the exact nature of the copper-rich phases segregating at the grain boundaries in CaCu3Ti4O12. Finally, the structural, microstructural and physical characterizations of all the polycrystalline ceramics and the single-crystal provide new arguments in the understanding of the dielectric properties of CaCu3Ti4O12

Nous présentons dans ce mémoire les résultats concernant la caractérisation spectroscopique spatiotemporelle de plasmas d'ablation laser obtenus à partir de cibles de céramiques d'oxydes complexes (CCTO et BSTO). Nos mesures montrent que les différentes espèces constituant le plasma évoluent de façons similaires quelque soit leur degré d'ionisation et ceci pour l'ensemble des conditions de pression et de fluence explorées. Nous montrons aussi que dans les premiers instants suivant l'impact laser, le plasma est fortement non-uniforme et se propage selon une seule dimension, il s'uniformise par la suite et s'expanse alors dans les trois dimensions. Une collaboration avec le laboratoire LP3 (Université de Marseille) nous a permis d'estimer les paramètres caractéristiques du plasma (température, densité électronique, épaisseur) à partir de la confrontation entre nos spectres expérimentaux et les résultats de la simulation de la radiance spectrale du plasma. A partir de cette confrontation, nous confirmons qu'il existe une forte corrélation entre l'inhomogénéité du plasma et son type d'expansion. Grâce à l'analyse spectrale il a été possible d'identifier et de quantifier des polluants présents dans les cibles, nous avons pu ainsi estimer des concentrations minimales pouvant atteindre la dizaine de ppm selon le type de polluant.

Nous présentons dans ce mémoire les résultats concernant la caractérisation spectroscopique spatiotemporelle de plasmas d’ablation laser obtenus à partir de cibles de céramiques d'oxydes complexes (CCTO et BSTO). Nos mesures montrent que les différentes espèces constituant le plasma évoluent de façons similaires quelque soit leur degré d'ionisation et ceci pour l'ensemble des conditions de pression et de fluence explorées. Nous montrons aussi que dans les premiers instants suivant l'impact laser, le plasma est fortement non-uniforme et se propage selon une seule dimension, il s’uniformise par la suite et s'expanse alors dans les trois dimensions. Une collaboration avec le laboratoire LP3 (Université de Marseille) nous a permis d'estimer les paramètres caractéristiques du plasma (température, densité électronique, épaisseur) à partir de la confrontation entre nos spectres expérimentaux et les résultats de la simulation de la radiance spectrale du plasma. A partir de cette confrontation, nous confirmons qu'il existe une forte corrélation entre l'inhomogénéité du plasma et son type d'expansion. Grâce à l'analyse spectrale il a été possible d'identifier et de quantifier des polluants présents dans les cibles, nous avons pu ainsi estimer des concentrations minimales pouvant atteindre la dizaine de ppm selon le type de polluant
From the laser ablation of complex oxide ceramics (CCTO and BSTO), characterisation by time-space resolved spectroscopy and fast imaging are shown in this dissertation. By the measurements, we noticed a similar development of all species of the plasma, for any ionisation degree, in any explored pressure and explored fluence. During the first times after laser impact, plasma is highly non-uniform and moves forward only one dimension. Afterwards, plasma expands uniformly in three dimensions. From collaboration with the LP3 laboratory (Marseille University), we succeeded in estimating plasma parameters (temperature, electronic density, thickness) from fits of experimental spectra with simulated ones. From those fits, we bore out the correlation between plasma non-uniformity and expansion kind. By spectral analysis it was possible to identify and quantify pollutants from targets. Depending on the pollutant, we were able to estimate weak concentrations, as low as few tens ppm

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico
With the recent advances in telecommunications industry in antenna area itâs increasingly required the development of ceramic materials which have high values of permittivity dielectric, low dielectric loss and a good thermal stability. Dielectric ceramics of CaCu3Ti4O12 are candidates as high values of permittivity dielectric materials and have been studied extensively. Nowadays ceramics offer materials several significant advantages in relation to others since present low production cost for electronic devices that operate of radio and microwave frequency, as well as being low weight materials, stable with temperature and extremely amenable to miniaturization. Sample preparation for structural analysis and dielectric, had the addition of CaCu3Ti4O12 to the phase MgTiO3 calcined in ratios of 4.0; 6.0; 8.0; 10.0 and 12.0 % by mass. The X-ray diffraction was important for the structural characterization of the obtained composite. The morphology of the samples was observed by Scanning Electron Microscopy (SEM). The dielectric characterization of radio frequency spectroscopy of impedance was performed which occurred two conductivity mechanisms for a sample. Models of dielectric relaxation approach the Cole-Cole and Havriliak-Negami type model. The experiments indicated that it is possible to obtain ceramic composites with good values of dielectric permittivity and low dielectric losses, resulting in scalebility and efficiency for devices designed to operate in those frequencies. Numerical simulation was performed with samples verifying good agreement with the experimental data. They studied the BiNbO4 phase doped with copper oxide and its possible applications in RF and Microwave. Addition of CaCu3Ti4O12 with MgTiO3 matrix contributed to the reduction of temperature coefficient of resonant frequency -39.25 ppm/ÂC to 9.62 ppm/ÂC, increased dielectric permittivity and dielectric loss. This thesis also presents a proposal for samples act as dielectric resonator antennas in the frequency range of 5.4 GHz to 6.1 GHz (C-band).The composites evaluated in this work has behaved properly as materials for use in microwave
Com os recentes avanÃos da indÃstria de telecomunicaÃÃes na Ãrea de antenas se faz cada vez mais necessÃrio o desenvolvimento de materiais cerÃmicos que apresentem altos valores de permissividade dielÃtrica, baixa perda dielÃtrica e uma boa estabilidade tÃrmica. CerÃmicas dielÃtricas CaCu3Ti4O12 sÃo candidatas como materiais de elevado valor de permissividade dielÃtrica e tÃm sido estudadas amplamente. Hoje as cerÃmicas oferecem vÃrias vantagens por apresentarem baixo custo de produÃÃo para dispositivos eletrÃnicos que operam em radiofrequÃncia e micro-ondas, alÃm de serem materiais de peso pequeno, estÃveis com a temperatura e extremamente passÃveis de miniaturizaÃÃo. A preparaÃÃo das amostras para anÃlise estrutural e dielÃtrica, teve a adiÃÃo de CaCu3Ti4O12 à fase MgTiO3 calcinada, em proporÃÃes de 4,0; 6,0; 8,0; 10,0 e 12,0 % em massa. A difraÃÃo de raios-X foi importante na caracterizaÃÃo estrutural dos compÃsitos obtidos. A morfologia das amostras foi estudada pela microscopia eletrÃnica de varredura (MEV). A caracterizaÃÃo dielÃtrica em rÃdio frequÃncia foi realizada por Espectroscopia de ImpedÃncia na qual se verificaram dois mecanismos de condutividade para uma das amostras analisadas. Os modelos de relaxaÃÃo dielÃtrica se aproximam do modelo do tipo Cole-Cole e Havriliak-Negami. Os experimentos realizados indicaram que à possÃvel obter compÃsitos cerÃmicos com bons valores de permissividade dielÃtrica e baixas perdas dielÃtricas, resultando em compactaÃÃo e eficiÃncia para dispositivos a serem projetados. SimulaÃÃo numÃrica foi realizada com as amostras verificando-se boa concordÃncia com os dados experimentais. Foram estudadas a fase BiNbO4 dopada com CuO e suas possÃveis aplicaÃÃes em radiofrequÃncia e micro-ondas. A AdiÃÃo de CaCu3Ti4O12 à matriz MgTiO3 contribuiu para a reduÃÃo do coeficiente de temperatura da frequÃncia de ressonÃncia de -39,25 ppm/ÂC para 9,62 ppm/ÂC, com o aumento da permissividade dielÃtrica e da perda dielÃtrica. Este trabalho de tese tambÃm apresenta uma proposta para as amostras funcionarem como antenas ressonadoras dielÃtricas na faixa de frequÃncias de 5,4 GHz a 6,1 GHz (banda C). Os compÃsitos avaliados nesse trabalho comportaram-se adequadamente como materiais para uso em micro-ondas.

OLIVEIRA, P. W. S. Estudo das propriedades dilétricas em microondas das matrizes MgTiO3 (MTO) - CaCu3Ti4O12 (CCTO) e BiNbO4 – CuO e sua estabilidade térmica para o uso em sistemas de comunicação. 122 f. 2015. Tese (Doutorado em Engenharia de Teleinformática) – Centro de Tecnologia, Universidade Federal do Ceará, Fortaleza, 2015.
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With the recent advances in telecommunications industry in antenna area it’s increasingly required the development of ceramic materials which have high values of permittivity dielectric, low dielectric loss and a good thermal stability. Dielectric ceramics of CaCu3Ti4O12 are candidates as high values of permittivity dielectric materials and have been studied extensively. Nowadays ceramics offer materials several significant advantages in relation to others since present low production cost for electronic devices that operate of radio and microwave frequency, as well as being low weight materials, stable with temperature and extremely amenable to miniaturization. Sample preparation for structural analysis and dielectric, had the addition of CaCu3Ti4O12 to the phase MgTiO3 calcined in ratios of 4.0; 6.0; 8.0; 10.0 and 12.0 % by mass. The X-ray diffraction was important for the structural characterization of the obtained composite. The morphology of the samples was observed by Scanning Electron Microscopy (SEM). The dielectric characterization of radio frequency spectroscopy of impedance was performed which occurred two conductivity mechanisms for a sample. Models of dielectric relaxation approach the Cole-Cole and Havriliak-Negami type model. The experiments indicated that it is possible to obtain ceramic composites with good values of dielectric permittivity and low dielectric losses, resulting in scalebility and efficiency for devices designed to operate in those frequencies. Numerical simulation was performed with samples verifying good agreement with the experimental data. They studied the BiNbO4 phase doped with copper oxide and its possible applications in RF and Microwave. Addition of CaCu3Ti4O12 with MgTiO3 matrix contributed to the reduction of temperature coefficient of resonant frequency -39.25 ppm/°C to 9.62 ppm/°C, increased dielectric permittivity and dielectric loss. This thesis also presents a proposal for samples act as dielectric resonator antennas in the frequency range of 5.4 GHz to 6.1 GHz (C-band).The composites evaluated in this work has behaved properly as materials for use in microwave
Com os recentes avanços da indústria de telecomunicações na área de antenas se faz cada vez mais necessário o desenvolvimento de materiais cerâmicos que apresentem altos valores de permissividade dielétrica, baixa perda dielétrica e uma boa estabilidade térmica. Cerâmicas dielétricas CaCu3Ti4O12 são candidatas como materiais de elevado valor de permissividade dielétrica e têm sido estudadas amplamente. Hoje as cerâmicas oferecem várias vantagens por apresentarem baixo custo de produção para dispositivos eletrônicos que operam em radiofrequência e micro-ondas, além de serem materiais de peso pequeno, estáveis com a temperatura e extremamente passíveis de miniaturização. A preparação das amostras para análise estrutural e dielétrica, teve a adição de CaCu3Ti4O12 à fase MgTiO3 calcinada, em proporções de 4,0; 6,0; 8,0; 10,0 e 12,0 % em massa. A difração de raios-X foi importante na caracterização estrutural dos compósitos obtidos. A morfologia das amostras foi estudada pela microscopia eletrônica de varredura (MEV). A caracterização dielétrica em rádio frequência foi realizada por Espectroscopia de Impedância na qual se verificaram dois mecanismos de condutividade para uma das amostras analisadas. Os modelos de relaxação dielétrica se aproximam do modelo do tipo Cole-Cole e Havriliak-Negami. Os experimentos realizados indicaram que é possível obter compósitos cerâmicos com bons valores de permissividade dielétrica e baixas perdas dielétricas, resultando em compactação e eficiência para dispositivos a serem projetados. Simulação numérica foi realizada com as amostras verificando-se boa concordância com os dados experimentais. Foram estudadas a fase BiNbO4 dopada com CuO e suas possíveis aplicações em radiofrequência e micro-ondas. A Adição de CaCu3Ti4O12 à matriz MgTiO3 contribuiu para a redução do coeficiente de temperatura da frequência de ressonância de -39,25 ppm/°C para 9,62 ppm/°C, com o aumento da permissividade dielétrica e da perda dielétrica. Este trabalho de tese também apresenta uma proposta para as amostras funcionarem como antenas ressonadoras dielétricas na faixa de frequências de 5,4 GHz a 6,1 GHz (banda C). Os compósitos avaliados nesse trabalho comportaram-se adequadamente como materiais para uso em micro-ondas.

Ces dernières années, des matériaux céramiques présentant une permittivité relative colossale ont été découverts. Les premiers travaux de recherche ont montré qu'une forte corrélation existe entre les propriétés électriques et la structure de ces matériaux. Ainsi, plusieurs types de caractérisations électriques ont été entrepris. La mesure par spectroscopie d'impédance est, de loin, la plus utilisée ; elle a permis à partir d'une modélisation par des circuits électriques équivalents d'avancer quelques hypothèses sur une polarisation interfaciale. Jusqu'à présent, ces interprétations sont toujours sujet à discussion et aucun modèle ne tient en compte toutes les propriétés connues pour ces matériaux, plus particulièrement, une réponse directionnelle (non symétrique) par rapport au champ électrique. L'enjeu de ce travail est de savoir s'il y a une relation entre toutes les caractéristiques de ces matériaux et d'avoir une explication par des mécanismes physiques les plus simples possibles de l'origine de la permittivité colossale. Des travaux antérieurs ont montré l'importance des effets d'interfaces dans ces matériaux à permittivité colossale, qu'ils soient associés à leurs contacts avec les électrodes métalliques, ou bien à une non homogénéité électrique entre les grains et les joints de grains qui les constituent. Afin de comprendre quelles sont les interfaces qui contrôlent les comportements de ces matériaux, et spécialement leur réponse non symétrique, un panel de caractérisations électriques ont été effectuées ; aussi bien à l'échelle macroscopique (pastille du matériau métallisé) qu'à un niveau local de grains et joints de grains individuels ; avec un soin particulier à la qualité des mesures (conditions, reproductibilité. . . Etc). Les résultats de ce panel élargi de caractérisations sont analysés et confrontés aux modèles existants dans la littérature afin d'améliorer ou de proposer un nouveau modèle qui décrit le plus complètement possible ce type de matériaux. Les caractérisations électriques du CCTO (CaCu3Ti4O12) ont montré des propriétés différentes de celles des matériaux diélectriques classiques, notamment la nonsymétrie et la " faible résistivité " qui mènent à reconsidérer la nature diélectrique de ce type de matériaux. Une caractérisation capacité-tension (C-V) utilisé habituellement pour caractériser les matériaux semi-conducteurs a révélé une structure de type Métal/Isolant/Semi-conducteur au contact matériau/électrodes. Une telle structure arrive à corréler les différents comportements électriques du matériau et à expliquer l'origine de la permittivité colossale apparente observée dans ces matériaux
In recent years, ceramic materials presenting a colossal relative permittivity have been largely studied. The first research works showed that a strong correlation exists between the electric properties and the structure of these materials. Impedance spectroscopy measurement is, by far, the most used one; it allowed from a modeling by electrical equivalent circuits to advance some hypotheses on an interfacial polarization. Until now, these interpretations are subject to discussion and no model takes into account all the known properties of these materials; particularly, the directional response (nonsymmetrical) in regard of the applied electrical field is still unexplained. The aim of this work is to know if there is a relation between all the characteristics of these materials to the microstructure, in order to understand the underlying physical mechanisms responsible of the observed colossal permittivity. Previous works showed the importance of interfaces effects on these colossal permittivity materials; even they are associated to their contacts with the metallic electrodes, or to an electrical heterogeneity of their microstructure composed of grains and grain boundaries. To understand which interfaces control the behavior of these materials, and specially their non-symmetrical response, a panel of electrical characterizations were made; both at the macroscopic scale (pellet of the metalized material) as at a local level of individual grains and grain boundaries; with a particular care in the quality of the measurements (conditions, reproducibility. . . Etc. ). Results of this widened panel of characterizations are analyzed and confronted to the existing models in order to amend the model that describes this type of materials. The electrical characterizations of the CaCu3Ti4O12 (CCTO) showed properties different from those of classical dielectric materials, in particular the non-symmetry and a "low resistivity" which lead to better define the scope where the material can be considered as a dielectric. A capacitance-voltage (C-V) characterization usually used to evaluate semiconductor materials revealed a Metal/ Insulator/Semiconductor structure at the material/electrode contact. Such a structure is proposed to explain some of the electric behavior of this material particularly the non-symmetrical response observed in these colossal dielectric constant materials

Mestrado em Engenharia Física
A necessidade de produção de dispositivos eletrónicos mais eficientes e a sua miniaturização tem sido um dos principais desígnios da indústria eletrónica. Assim surgiu a necessidade de melhorar o desempenho das designadas placas de circuito impresso, tornando-as simultaneamente mais flexíveis, com menos ruído, mais estáveis face a variações bruscas de temperatura e que permitam operar numa vasta gama de frequências e potências. Para tal, uma das estratégias que tem vindo a ser estudada é a possibilidade de incorporar os componentes passivos, nomeadamente condensadores, sob a forma de filme diretamente no interior da placa. Por forma a manter uma elevada constante dielétrica e baixas perdas, mantendo a flexibilidade, associada ao polímero, têm sido desenvolvidos os designados compósitos de matriz polimérica. Nesta dissertação procedeu-se ao estudo do comportamento dielétrico e elétrico da mistura do cerâmico CaCu3Ti4O12 com o copolímero estireno-isoprenoestireno. Foram preparados filmes com diferentes concentrações de CCTO, recorrendo ao método de arrastamento, em conjunto com o Centro de Polímeros da Eslováquia. Foram também preparados filmes por spin-coating para as mesmas concentrações. Usaram-se dois métodos distintos para a preparação do pó de CCTO, reação de estado sólido e sol-gel. Foi realizada a caraterização estrutural (difração de raios-X. espetroscopia de Raman), morfológica (microscopia eletrónica de varrimento) e dielétrica aos filmes produzidos. Na caracterização dielétrica determinou-se o valor da constante dielétrica e das perdas para todos os filmes, à temperatura ambiente, bem como na gama de temperatura entre os 200 K e os 400 K, o que permitiu identificar existência de relaxações vítreas e subvítreas, e assim calcular as temperaturas de transição vítrea e energias de ativação, respetivamente. Foram realizados testes de adesão e aplicada a técnica de análise mecânica dinâmica para o cálculo das temperaturas de transição vítrea nos filmes preparados pelo método de arrastamento. Estudou-se ainda qual a lei de mistura que melhor se ajusta ao comportamento dielétrico do nosso compósito. Verificou-se que é a lei de Looyenga generalizada a que melhor se ajusta à resposta dielétrica dos compósitos produzidos.
The need for production of more efficient electrical appliances and their miniaturization has been one of the main purposes of the electronic industry. In this context came the need to improve the performance of designated printed circuit boards, while making them more flexible, less noise, more stable in the face of sudden changes in temperature and in order to operate in a wide range of frequencies and powers. To this end, a strategy which has been studied is the possibility of incorporating passive components, including capacitors in the form of film directly inside the card. In order to maintain a high dielectric constant, low loss, associated characteristics to the ceramic while maintaining the flexibility associated with the polymer composite polymer matrix have been created. In this thesis we studied the dielectric and electrical behavior of CaCu3Ti4O12 ceramic mixing with the styrene-isoprene-styrene copolymer. Films were prepared with different concentrations of CCTO using the entrainment method prepared in cooperation with the Slovakia polymers center. Films were also prepared by spin-coating in Aveiro for the same concentrations. Two different methods were used for the preparation of CCTO powder, solid state reaction and sol-gel. To the obtained films was made structural characterization (X-ray diffraction. Raman spectroscopy), morphological (scanning electron microscopy) and the dielectric characterization. In the dielectric characterization the value of the dielectric constant and losses for all films prepared at room temperature (300 K) was studied and the study at variable temperature (200K-400K) was used to determine whether or not the existence of relaxations subvitreous and vitreous and thereby calculate the glass transition temperatures and activation energies, respectively. Adhesion tests were made and the dynamic mechanical analysis technique applied to calculate the glass transition temperature in the films prepared in Bratislava. The best law mix that adapts to the behavior of our composite was studied being the generalized Looyenga the one that provides the best fit.

Des grains nanométriques de titanate de baryum ont été obtenus par synthèse hydrothermale à 150 et 250°C et à partir de précurseur BaCl2. 2H2O/TiCl3 ou TiO2,. Le frittage à 1250°C pendant 10 ou 20 h a conduit à descéramiques de densité supérieure à 95%. Ces céramiques présentent une structure bimodale constituée de gros grains (60 µm) dans une matrice de petits grains (1µm). Des permittivités électriques relatives supérieures à 7000 (poudre ex-TiCl3) ou à 11000 (poudre ex-TiO2) sont notées à la température de Curie. Les couches épaisses présentent une permittivité supérieure à 4000. Des poudres de BaTiO3 dopé au lanthane ont été préparées par coprécipitation. Les céramiques correspondantes présentent une microstructure homogène. La température de Curie diminue et la permittivité relative augmente jusqu'à 10 000 avec l'augmentation de la teneur en La3+. Les matériaux frittés par SPS montrent des propriétés électriques exceptionnelles. Des matériaux à base de CaCu3Ti4O12 a été préparés par coprécipitation. Les céramiques obtenues présentent de très bonnes caractéristiques électriques liées à la présence de phases supplémentaires de CuO
Nanometric powders of BaTiO3 have been prepared by hydrothermal method at 150 and 250°C using BaCl2. 2H2O/TiCl3 or TiO2 as precursors. Ceramics showing 95% of densification are obtained after sintering at 1250°C for 10 and 20 h. These ceramics present a heterogeneous microstructure. The grain size and the grain distribution in the ceramic bulk govern the electrical properties. Thick layers present a relative permittivity higher then 4000 at the curie temperature. La-doped BaTiO3 has been prepared by the oxalate method. The obtained ceramics showed a uniform microstructure. The Curie temperature is displaced to lower temperatures and the relative permittivity increases up to 10000 with increasing La3+ concentration. Ceramics sintered by spark plasma sintering showed electrical properties that are significantly different from those of conventionnally sintered ones. The coprecipitation has been used to synthesize materials based on CaCu3Ti4O12. Three main types of ceramics were obtained. The presence of CuO phase beside the CCT plays an important role for enhancing the dielectric properties

碩士
正修科技大學
電機工程研究所
97
Calcium copper titanium oxide (CaCu3Ti4O12, CCTO) films were deposited on Pt/Ti/SiO2/Si substrates at room temperature (RT) by radio frequency magnetron sputtering. The effects of the rf power (60~120 W), thin film thickness (0.43~1.92 µm) and the oxygen concentration (0~80%) on the dielectric properties of CCTO films were discussed. As-deposited CCTO films were annealed at various temperatures (500, 600 and 700℃) and atmosphere (vacuum, N2 and O2) by a rapid thermal process (RTP). The XRD patterns and SEM images demonstrated that the crystalline structures and surface morphologies of CCTO thin films were sensitive to the post-annealing temperature and post-annealing atmosphere. The polycrystalline of CCTO films could be obtained when the post-annealing temperature at 700℃ in oxygen atmosphere. The optimal deposition conditions of CCTO films were rf power of 80 W, deposition time of 2 h (the thickness of film is about 0.8 µm), oxygen concentration of 60% at RT, which exhibits a dielectric constant of 87.7, a dielectric loss of 0.04 (at 10 kHz) and a leakage current of 3.82×10-6 A/cm2 (at 25 kV/cm). The as-deposited CCTO films were annealed at 700℃ in oxygen atmosphere with a RTP exhibits a high dielectric constant of 410, a dielectric loss of 0.17 (at 10 kHz) and a leakage current of 1.28 10-5A/cm2 (at 25 kV/cm).

碩士
臺灣大學
物理研究所
95
The dielectric properties of (CaCu3Ti4O12)1-x(Fe3O4)x (x = 0.01, 0.05, 0.1, 0.2, 0.3 and 0.4) have been studied, only 1% mixing of Fe3O4 dramatically quenches the huge of 104 down to 65 over the measured temperature range from 15 K to 300 K. At low T, CaCu3Ti4O12 (CCTO) transforms into an antiferromagnetic phase at TN = 25 K. The dielectric constant of (CaCu3Ti4O12)1-x(Fe3O4)x (x = 0.01, 0.05, 0.1, 0.2 and 0.3) shows sharp decrease below TN, providing possible coupling between the polarization and magnetization. In addition, the (CCTO)0.95(Fe3O4)0.05 and (CCTO)0.9(Fe3O4)0.1 ceramics have also shown diffuse phase transition (DPT), which is a typical feature of relaxor ferroelectrics. The modified Curie–Weiss law and Santos-Eiras equation were applied to (CCTO)0.95(Fe3O4)0.05 and (CCTO)0.9(Fe3O4)0.1 ceramics in order to investigate the nature of polarization mechanism. Furthermore, physical parameters such as static freezing temperature TVF fitted by the Vogel–Fulcher relationship, indicated the relaxor nature of these two ceramics.

碩士
崑山科技大學
電子工程研究所
99
In this paper, phase formation, microstructure and dielectric properties of Nb-doped CaCu3Ti4O12 (CCTO) dielectric ceramics by reaction- sintering process were investigated. Single phase CCTO could be obtained after 2h sintering. A maximum density 4.9 g/cm3 and a maximum shrinkage 16.72% were found for CaCu3Ti4O12 ceramics sintered at 1120oC/4h. εr=7450 (30oC,100kHz), tanδ=0.1 (30oC,100kHz) and τε=0.17 %/oC (100kHz) were found for 1120oC/6h sintering CCTO. Single phase CaCu3Ti4-xNbxO12+x/2 ceramics were also obtained. A density 4.9g/cm3 and a shrinkage 17.36% were found at x=0.15 for 1130oC/6h sintering . εr=8695 (30oC,100kHz) were found at x=0.15 for 1130oC/6h sintering . tanδ=0.016 (30oC,100kHz) were found at x=0.02 for 1110oC/2h sintering . τε=0.02 %/oC (100kHz) were found at x=0.02 for 1110oC/6h sintering .

Nous présentons dans ce mémoire les résultats concernant la caractérisation spectroscopique spatiotemporelle de plasmas d’ablation laser obtenus à partir de cibles de céramiques d'oxydes complexes (CCTO et BSTO). Nos mesures montrent que les différentes espèces constituant le plasma évoluent de façons similaires quelque soit leur degré d'ionisation et ceci pour l'ensemble des conditions de pression et de fluence explorées. Nous montrons aussi que dans les premiers instants suivant l'impact laser, le plasma est fortement non-uniforme et se propage selon une seule dimension, il s’uniformise par la suite et s'expanse alors dans les trois dimensions. Une collaboration avec le laboratoire LP3 (Université de Marseille) nous a permis d'estimer les paramètres caractéristiques du plasma (température, densité électronique, épaisseur) à partir de la confrontation entre nos spectres expérimentaux et les résultats de la simulation de la radiance spectrale du plasma. A partir de cette confrontation, nous confirmons qu'il existe une forte corrélation entre l'inhomogénéité du plasma et son type d'expansion. Grâce à l'analyse spectrale il a été possible d'identifier et de quantifier des polluants présents dans les cibles, nous avons pu ainsi estimer des concentrations minimales pouvant atteindre la dizaine de ppm selon le type de polluant
From the laser ablation of complex oxide ceramics (CCTO and BSTO), characterisation by time-space resolved spectroscopy and fast imaging are shown in this dissertation. By the measurements, we noticed a similar development of all species of the plasma, for any ionisation degree, in any explored pressure and explored fluence. During the first times after laser impact, plasma is highly non-uniform and moves forward only one dimension. Afterwards, plasma expands uniformly in three dimensions. From collaboration with the LP3 laboratory (Marseille University), we succeeded in estimating plasma parameters (temperature, electronic density, thickness) from fits of experimental spectra with simulated ones. From those fits, we bore out the correlation between plasma non-uniformity and expansion kind. By spectral analysis it was possible to identify and quantify pollutants from targets. Depending on the pollutant, we were able to estimate weak concentrations, as low as few tens ppm

碩士
國立成功大學
材料科學及工程學系碩博士班
98
CaCu3Ti4O12(CCTO) is a dielectric material which has pervoskite structure. This material has ultrahigh dielectric constant (about 104~105) at room temperature, and it is independent of temperature. The mechanism for inducing large dielectric response of CaCu3Ti4O12 still remains unresolved. Presently, grain boundary and domain boundary are thought as the origin of such ultrahigh dielectric constant. In this research, we analyze the dielectric behavior of MST- doped CaCu3Ti4O12 and the existence of electrode-contact effect.

碩士
大同大學
材料工程學系(所)
96
The CaCu3Ti4O12 (CCTO)is a cubic perovskite structure. It has s a large dielectric constant which is independent of temperature. The mechanism for inducing the huge dielectric response of CaCu3Ti4O12 still remains unresolved. The CaCu3Ti4O12 with high dielectric constant does not need any additives.This thesis is syudy the effect oh additives on the properties of CaCu3Ti4O12 ceramic.The CaCu3Ti4O12 were additived included MgO、MnO、ZnO by traditional ceramic fabrication.

碩士
國立交通大學
電子工程系所
94
The high dielectric constant material CaCu3Ti4O12 (CCTO) is studied by conventional oxide powder mixing and sol-gel processing. For bulk samples, the effects of sintering temperature and sintering time are discussed. With changing the sintering temperature and sintering time, we can obtain that the dielectric constant increase with increasing sintering temperature and time. 95.2% relative density, 28000 dielectric constant, and 0.16 loss tangent at 1 kHz can be achieved by sintering at 1100�窢 for 20 hrs. The increase in dielectric constant can be attributed to the increase in average grain size, which is consistent with the grain boundary (internal) barrier layer capacitance (IBLC) theory. For CCTO thin films, we change the annealing temperature from 500�n�窢 to 800�n�窢 and find that the lowest annealing temperature for CCTO thin film to crystallize is 700�n�窢. The dielectric constant also increases with increasing annealing temperature. It can also be attributed to the increase in average grain size. At room temperature, the dielectric constant and loss tangent of CCTO thin film with annealing temperature at 800�n�窢 for 1 hr are about 1224 and 0.179 at 100 kHz, respectively.

碩士
正修科技大學
機電工程研究所
95
In this study, we adopt conventional solid-state reaction method to obtain CaCu3Ti4O12 (CCTO) ceramics. The effect of sintering conditions on the microstructures and the electrical properties of CCTO ceramics are also discussed. Experimental results reveal that the calcined temperature of CCTO was 900℃. However, crystal phases of polycrystalline CCTO ceramics have no obvious differences using by XRD. It is found that there are no strong change of crystalline phase intensity at various sintering temperature and dwell time. It can be seen that the grain size was significantly increased with an increase of sintering temperature and dwell time. However, it is observed that the liquid-phase secondary recrystallization of CCTO ceramics at sintering temperature 1010℃. Besides, 75% CuO doped in CaTiO3 and then formed CCTO (75% copper ions replaces the position of calcium ions)， the lattice constant will extend one-fold. The grain size increased with an increase of Cu stoichiometric ratio, 75% Cu stoichiometric ratio of CCTO exhibited a high dielectric constant. The dielectric constant was found to be constant at sintering temperature 1000℃ for 24 h (ε：about 700, tanδ：below 0.2) at 10 kHz. However, sintering temperature at 1100℃ for 24 h exhibited a high dielectric constant (ε：about 10000, tanδ：below 0.8) at 10 kHz but dielectric constant rapidly decreased with an increase of frequency. In addition, the increase of Cu stoichiometric ratio, sintering temperature and dwell time will increase the oxygen vacancy and result in conductivity from isolation transform to semi-conduction.

碩士
國立交通大學
電子工程系所
95
Electrical behaviors, physical and chemical properties of the high dielectric constant material CaCu3Ti4O12 (CCTO) derived from sol-gel methods is investigated in this study. The effects of thicknesses and annealing conditions on the electrical properties of CCTO thin films are discussed as well. The dielectric constant of CCTO thin films decreases with increasing film thicknesses. Both the dielectric constant of CCTO thin films and interlayer are calculated based on the equivalent circuit models, which are explored to explain the thickness dependence of the dielectric constant of CCTO films. Carrier conduction mechanisms of CCTO thin films at low and high electric fields are Ohmic conduction and Frenkel-Poole emission, respectively.

碩士
國立高雄應用科技大學
機械與精密工程研究所
104
The CaCu3Ti4O12 (CCTO) is a material with perovskite structure. It has ultrahigh dielectric constant (about 104~105) and almost remains constant at room temperature. However, some of the studies have indicated the CCTO with high dielectric constant must grow into large grains under the longer sintering period and it is unfavorable for the industrial production. Therefore, how to shorten the sintering time is an important issue. In this study, the CCTO powder was synthesized by the solid state synthesis and then mixed with CuO. The effects on the microstructure and electrical properties with different concentrations and sintering times for the CCTO by liquid phase sintering were discussed. In this study, the dielectric loss and dielectric constant for the CCTO were decreased by adding CuO. The same dielectric constants could be obtained by adding 2 % CuO and sintering for 5 hr and 1% CuO and sintering for 10 hr. By the TEM analysis, the disorder in crystal and low angle grain boundary were observed. The impedance analysis confirmed the dielectric mechanism is due to the local disorder which caused the local grain metallization by adding the CuO.

碩士
國立交通大學
電子工程系所
96
Recently, many kinds of new nonvolatile memory manufactured from different materials have attracted great attention. The resistance random access memory (RRAM) which has bistable resistive switching character started to attract the research community’s interest again as a nonvolatile, low power, high density, and multi-bit operating memory. Accordingly, RRAM has been proposed to be one candidate of next generation nonvolatile memories. In this study, the bistable resistance switching characteristics of CaCu3Ti4O12 (CCTO) films prepared by sol-gel method and annealed at various temperatures are investigated. The correlation between resistance switching behaviors and crystallinity of the films are also explored. The resistance switching mechanisms are investigated by the impedance spectroscopy technique. The equivalent circuit and physical model for resistance switching are proposed. Finally, the effects of the electrode materials are also examined.

碩士
國立成功大學
資源工程學系碩博士班
94
CaCu3Ti4O12 which exhibits a large dielectric constant and the dielectric constant is weakly varying in the temperature range 100~400K. This property is conformed to the electronic component’s application specification, for example X5R.But the large tangent loss makes it can not conform to the application specification. This study is to investigate the origin of high permittivity in CaCu3Ti4O12 and the effects of LiF addition to CaCu3Ti4O12. Through these investigations a large resistivity and process in preparing for CaCu3Ti4O12 could be suggested.

碩士
長庚大學
電子工程學系
98
In this study, we investigated the switching behaviors of CaCu3Ti4O12(CCTO) with different work function materials as electrode. CCTO was deposited by RF sputter and annealed at various temperatures. The relationship between the crystalline of the CCTO and the initial resistance state of the devices was discussed. The operation voltage and retention of devices were measured by I-V sweep mode. There was no data loss at the nondestructive readout test for over 5000 seconds. The effect of the CCTO grain size on the operation voltage of the device was also explored. The leakage current of the device could be improved by using high work function metal electrode and annealing process. The operation voltage of the device decreased as the annealing temperature increased.

碩士
國立成功大學
材料科學及工程學系碩博士班
92
We describe the material, cubic perovskite CaCu3Ti4O12 (CCTO) , which exhibits a large dielectric response, the temperature-dependence of which has not been seen in any existing material to our knowledge. Dielectric constants for CCTO is found to be much higher than expected based on the dielectric polarizabilities of the constituent atoms, and this property seems not to be related to either underlying ferroelectric or relaxor behavior. X-ray diffraction and thermodynamic data argue against an explanation in terms of ferroelectricity, i.e. the collective ordering of local dipole moments. 　　It is known that addition of copper to BaTiO3 or SrTiO3 can lead to greatly enhanced dielectric constant through the barrier layer mechanism. We prepared samples of CCTO that were copper deficient, which might be expected to preclude a copper rich phase at the grain boundaries. It’s found that the copper deficiency does indeed result in a lower dielectric constant. 　　In this paper, we would like clarify the effect of Cu stoichiometry on the microstructure and dielectric behavior of CCTO.

碩士
大同大學
材料工程學系(所)
104
Many of the capacitor dielectric material is difficult to be designed thinner. In the microelectronics industry, the dispersion component accounted for 90% of the area of the circuit board, wherein the capacitor is a main object, and as such hinders the miniaturization of the capacitor development. Footprint embedded capacitor is small, you can make the packing density of the circuit board has improved significantly, the development and application of embedded capacitor is very important. CaCu3Ti4O12 (CCTO) dielectric ceramics are of concern in recent years, high dielectric material has a high dielectric constant at a frequency of 10Hz and a stable temperature in the range of 100-400K, CaCu3Ti4O12 (CCTO) / polymer composite dielectric material the more research attention. This study will be prepared by solid state reaction CaCu3Ti4O12 powder, a planetary ball mill CaCu3Ti4O12 powder fining with different proportions of carbon black mixed in different proportions filled PMMA prepare a dielectric composite material, the dielectric properties, used in embedded capacitors.

碩士
大同大學
材料工程學系(所)
103
If the temperature range of 100~400K, dielectric constant of CaCu3Ti4O12(CCTO) is almost independent of temperature. At room temperature and frequency less than 100kHz, the dielectric constant CCTO can reach 10000, which made it to have a high potential in application on high storage density, component of thin film and high dielectric capacitor. In this study CaCO3, CuO, TiO2 were used to fabricate CaCu3Ti4O12 powder by traditional ceramic fabrication process. Low Density Polyethylene(LDPE) was used for matrix to make CaCu3Ti4O12/LDPE composites. XRD, SEM, LCR meter were use to study micro-structure and dielectric properties.

碩士
國立成功大學
材料科學及工程學系碩博士班
97
CaCu3Ti4O12(CCTO) is a dielectric ceramic material which has pervoskite structure. This material has ultrahigh dielectric constant (about 104~105) at room temperature, and almost remain constant between 100K~600K. Recently, grain boundary and domain boundary are thought as the origin of such ultrahigh dielectric constant. Sintering conditions and raw materials have great influence on those boundaries. In this research, We get undoped CaCu3Ti4O12 powder with CaCO3、CuO、TiO2 stoichiometrily by solid state reaction at first. Then doping compounds consist Mn、Si、Ti elements (MST) and discuss it’s effects on dielectric properties and microstructure with different concentrations and sintering times, in addition, the probable mechanisms of those properties in CaCu3Ti4O12.

High dielectric constant materials are of technological importance as they lead to the miniaturization of the electronic devices. In this context, the observation of anomalously high dielectric constant (>104) in the body-centered cubic perovskite-related (Space group Im3) material Calcium Copper Titanate ((CaCu3Ti4O12)(CCTO)) over wide frequency (100 Hz – 1MHz at RT) and temperature (100 – 600 K at 1 kHz ) ranges has attracted a great deal of attention. However, high dielectric constant in CCTO is not well understood yet, though internal barrier layer capacitor (IBLC) mechanism is widely been accepted. Therefore, the present work has been focused on the preparation and characterization of CCTO ceramic and to have an insight into the origin of high dielectric constant. Influence of calcination temperature, processing conditions, microstructure (and hence grain size), composition, doping etc on the electrical characteristics of CCTO ceramics were investigated. Electrical properties were found to be strongly dependent on these parameters. The dielectric constant in CCTO was observed to be reduced considerably on substituting La+3 on Ca+2 site. The formation temperature of CCTO was lowered substantially (when compared to conventional solid-state reaction route) by adopting molten-salt synthesis. The dielectric loss in CCTO was reduced by incorporating glassy phases at the grain boundary. Potential candidates for the practical applications such as charge storage devices, capacitors etc, with dielectric constant as high as 700 at 300 K was accomplished in a three-phase percolative composite fabricated by incorporating Aluminium particle into CCTO-epoxy composite. Polycrystalline CCTO thin films with dielectric constant as high as ~ 5000 (1 kHz and 400 K) were fabricated on Pt(111)/Ti/SiO2/Si substrates using radio frequency magnetron sputtering. Effect of sintering conditions on the microstructural, ferroelectric and varistor properties of CCTO and LCTO ceramics belonging to the high and low dielectric constant members of ACu3M4O12 family of oxides were investigated in detail and are compared. Ferroelectric-like hysteresis loop (P vs E) and weak pyroelectricity were observed in CCTO and plausible mechanisms for this unusual phenomenon have been proposed.

碩士
國立成功大學
材料科學及工程學系碩博士班
95
An unusual dielectric ceramic material CaCu3Ti4O12 (CCTO) is a cubic perovskite structure. It possesses an extraordinarily high dielectric constant at room temperature of about 104~105. Besides, the dielectric constant is nearly constant over a wide temperature range ~100-600K. However the dielectric constant drops rapidly to 100 below about 100K. In this study, we would discuss the influence of MnO2 addition and electrode difference on the dielectric behavior and microstructure of CCTO. We can find that manganese doping would decrease the dielectric constant of CCTO. In addition, an equivalent circuit of CaSiO3-CCTO including domain, domain boundary, grain boundary, and electrode contact is proposed.

碩士
國立成功大學
資源工程學系碩博士班
95
CaCu3Ti4O12 which exhibits a large dielectric constant and the dielectric constant is weakly varying in the temperature range 100~400K. The mechanism for inducing the huge dielectric response of CaCu3Ti4O12 still remains unresolved. The existence of domains provides a reasonable explanation for dielectric behavior of single crystal and polycrystal CaCu3Ti4O12. In order to find more evidences about existence of domains, we try to discuss effects of CaSiO3-doped CaCu3Ti4O12 in this research.

碩士
國立成功大學
材料科學及工程學系碩博士班
96
CaCu3Ti4O12 is a remarkable dielectric material which exhibits a large dielectric constant and its dielectric constant is weakly sensitive to temperature range 100~400K. The purpose of this research is try to discuss effects to the dielectric constant and microstructure of CaCu3Ti4O12 by Ni doping and (Ni, Si) co-doping. According to the result, if the quantity of Ni doping or (Ni, Si) co-doping increases, the whole resistivity decreases, also the dielectric constant. But actually speaking, (Ni, Si) co-doping still enhances the dielectric constant larger than pure CaCu3Ti4O12, and more effective than Ni doping.

Ceramics and polymer-ceramic composites associated with high dielectric constants are of both scientific and industrial interest as these could be used in devices such as capacitors, resonators and filters. High dielectric constant facilitates smaller capacitive components, thus offering the opportunity to miniaturize the electronic devices. Hence there is a continued interest on high dielectric constant materials over a wide range of temperatures. Recently, CaCu3Ti4O12 (CCTO) ceramic which has centro-symmetric body centered cubic structure has attracted considerable attention due to its large dielectric constant (ε ~104-105) which is nearly independent of frequency (upto 10 MHz) and low thermal coefficient of permittivity (TCK) over 100-600K temperature range. Apart from the high dielectric ceramics, high dielectric polymer-ceramic composites have also become promising materials for capacitor applications. By combining the advantages of high dielectric ceramics and low leakage behaviour of polymers, one can fabricate new hybrid materials with high dielectric constants, and high breakdown field to achieve high volume efficiency and energy storage density for capacitor applications. The CCTO polycrystalline powders were generally prepared by the conventional solid-solid reaction route with CaCO3, TiO2 and CuO as the starting materials. This method of preparation often requires high temperatures and longer durations. To overcome these difficulties, in the present investigations, an attempt has been made to synthesize CCTO by adopting microwave assisted heating technique and wet chemical synthesis routes. Also the CCTO crystallites (size varying from nano to micrometers) incorporated in the Polyvinyliden fluoride (PVDF) and Polyaniline (PANI) matrix and several composites with high dielectric constants were fabricated and investigated. Further, the high dielectric constant glasses in the system (100-x)TeO2-xCaCu3Ti4O12, (x=0.5 to 3) were fabricated by the conventional melt-quenching technique and their structural and dielectric properties were studied. The results obtained pertaining to these aforementioned investigations are classified as follows. Chapter 1 is intended to give basic information pertaining to the dielectrics and various mechanisms associated with high dielectric constants. Brief exposure to the high dielectric constant materials is also given. The structural aspects of CCTO, various synthetic routes adopted for the synthesis and the origin of the dielectric anomaly in CCTO are elaborated. In addition, basic information about the high dielectric polymer-ceramic composites and glasses are provided. In chapter 2 the various experimental techniques that were employed to synthesize and characterize the materials under investigation were discussed. Chapter 3 reports the synthesis and characterization of CaCu3Ti4O12, (CCTO) powders by microwave assisted heating at 2.45 GHz, 1.1kW. The processing and sintering were carried out at different temperatures for varied durations. The optimum calcination temperature using microwave heating was found to be 950oC for 20 minutes to obtain cubic CCTO powders. This is found to be fast and energy efficient as compared to that of the conventional methods. The structure, morphology and dielectric properties of the CCTO ceramic processed by microwave assisted heating were studied via X-ray diffraction, Scanning electron microscopy (SEM) and impedance analyser. These studies revealed that, the microwave sintered (MS) samples were less porous than that of the conventional ones. Relative density of about 95% was achieved for the MS pellets (1000oC/60min) while for the conventional sintered (CS) pellets (1100oC/2h) it was only 91%. The dielectric constants for the microwave sintered (1000oC/60min) ceramics were found to vary from 11000 to 6950 in the 100 Hz to 100 kHz frequency range. The presence of larger grains (6-10μm) in the MS samples contributed to the higher dielectric constants. Chapter 4 deals with the synthesis of complex oxalate precursor, CaCu3(TiO)4(C2O4)8 • 9H2O, by the wet chemical route. The various trials and the different reaction schemes involved for the preparation of complex oxalate precursor were highlighted. The oxalate precipitate thus obtained was characterized by the wet chemical analyses, X-ray diffraction, FTIR absorption and TG/DTA analyses. The complex oxalate precursor, CaCu3(TiO)4(C2O4 )8.9H2O was subjected to thermal oxidative decomposition and the products of thermal decomposition were investigated employing XRD,TGA, DTA and FTIR techniques. Nanocrystallites of CaCu3Ti4O12 with the size varying from 30-200 nm were obtained at a temperature as low as 680oC. The nanocrystallites of CaCu3Ti4O12 were characterized using Electron Spin Resonance (ESR) and optical reflectance techniques. The selected area electron diffraction (SAED) pattern with the zone axis [012] and spot pattern in electron diffraction (ED) indicate their single-crystalline nature. The optical reflectance and ESR spectra indicate that the Cu (II) coordination changes from distorted octahedra to nearly flattened tetrahedra (squashed) to square planar geometry with increasing heat treatment temperature. The powders derived from the oxalate precursor have excellent sinterability resulting in high density ceramics which exhibited giant dielectric constants upto 40,000 (1 kHz) at 25oC, accompanied by low dielectric loss < 0.07. The effect of calcium content on the dielectric properties of CaxCu3Ti4O12 (x=0.90, 0.97, 1.0, 1.1 and 1.15) derived from the oxalate route was described in Chapter 5. The structural, morphological and dielectric properties of the ceramics were studied using X-ray diffraction, Scanning Electron Microscope along with Energy Dispersive X-ray Analysis (EDX), and Impedance analyzer. The X-ray diffraction patterns obtained for the x= 0.97, 1.0 and 1.1 ceramics could be indexed to a body– centered cubic perovskite related structure associated with the space group Im3. The microstructural studies revealed that the grains are surrounded by exfoliated sheets of Cu-rich phase. The microstructure that is evolved for the Ca0.97 ceramic more or less resembles that of the Ca1.0 ceramic, but the density of such exfoliated sheets of cu-rich phase is lesser for the Ca0.97 ceramic and none for Ca1.1 ceramic. The sintered pellet (x=0.97) was ground and thinned to the required thickness (~ 20nm) and analyzed using Transmission Electron Microscopy (TEM). The current-voltage (I-V) characteristics of the ceramics exhibited non-linear behaviour. The dielectric properties of these suggest that the sample corresponding to the composition x=0.97, has a reduced dielectric loss while retaining its high dielectric constant. Chapter 6 illustrates the results concerning the fabrication and characterization of nanocrystal composites of Polyaniline (PANI) and CaCu3Ti4O12 (CCTO). These were prepared using a simple procedure involving in-situ polymerization of aniline in dil. HCl. The PANI and the PANI-CCTO composites were subjected to X-ray diffraction, Fourier Transform Infrared (FTIR), Thermo gravimetric, Scanning Electron Microscopic (SEM) and Transmission electron microscopic analyses. The FTIR spectra recorded for the composites was similar to that of pure PANI unlike in the case of X-ray diffraction wherein the characteristics of both PANI and CCTO were reflected. The TGA in essence indicated the composites to have better thermal stability than that of pure PANI. The composite corresponding to 50%CCTO-50%PANI exhibited higher dielectric constant (4.6x106 @100Hz). The presence of the nano crystallites of CCTO embedded in the nanofibers of PANI matrix was established by TEM. The AC conductivity increased slightly upto 2kHz as the CCTO content increased in the PANI which was attributed to the polarization of the charge carriers. The value of dielectric constant obtained was higher than that of the other PANI based composites reported in the literature. Chapter 7 deals with the fabrication and characterization of diphasic Poly(vinylidene fluoride) (PVDF)-CCTO composite. The CCTO crystallites (size varying from nano to micrometers) incorporated in the Polyvinylidene fluoride (PVDF) and composites with varying CCTO content were fabricated. The structural, morphological and dielectric properties of the composites were studied using X-ray diffraction, Thermal analysis, Scanning Electron Microscope (SEM), Transmission Electron Microscopic (TEM) and Impedance analyzer. The room temperature dielectric constant as high as 95 at 100Hz has been realized for the composite with 0.55 Vol.fraction of CCTO (micro sized crystallites), which has increased to about 190 at 150oC. Whereas, the PVDF/CCTO nanocrystal composite with 0.13Vol.fraction of CCTO has exhibited higher room temperature dielectric constant (90 at 100Hz). The PVDF/CCTO nanocrystal composite was further investigated for the breakdown strength and electric modulus. The breakdown strength plotted against the dielectric constant evidenced an inverse relationship of breakdown voltage with the dielectric constant. The relaxation processes associated with these composites were attributed to the interfacial polarization or Maxwell-Wagner-Sillars (MWS) effect. Various theoretical models were employed to rationalize the dielectric behavior of these composites. The fabrication and characterization details of optically clear colored glasses in the system (100-x)TeO2-xCaCu3Ti4O12, (x=0.5 to 3 mol%) are reported in Chapter 8. The color varies from olive green to brown as the CaCu3Ti4O12 (CCTO) content increased in TeO2 matrix. The X-ray powder diffraction and differential scanning calorimetric analyses that were carried out on the as-quenched samples confirmed their amorphous and glassy nature respectively. The optical transmittance of the glasses exhibited typical band-pass filter characteristics. The dielectric constant and loss in the 100 Hz-1MHz frequency range were monitored as a function of temperature (323K673K). The dielectric constant and the loss increased as the CCTO content increased in TeO2 at all the frequencies and temperatures under study. Further, the dielectric constant and the loss were found to be frequency independent in the 323-473 K temperature range. The value obtained for the loss at 1MHz was 0.0019 which was typical of low loss materials, and exhibited near constant loss (NCL) contribution to the ac conductivity in the 100Hz-1MHz frequency range. The electrical relaxation was rationalized using the electrical modulus formalism. These glasses are found to be more stable (a feature which may be of considerable interest) as substrates for high frequency circuit elements in conventional semiconductor industries. Thesis ends with summary and conclusions, though each chapter is provided with conclusions and complete list of references.