Estudo dos sistemas cerâmicos multifuncionais CaCu3-xSrxTi4O12 (x=0,00; 0,15; 0,30 e 3,00) na forma de pós, bulks e filmes finos
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Data
2019-03-29
Autores
Cortés Suárez, Johan Alexander
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Universidade Estadual Paulista (Unesp)
Resumo
Os sistemas cerâmicos à base de CaCu3Ti4O12 (CCTO) possuem alta potencialidade pelas várias aplicações tecnológicas como: capacitores, memórias resistivas, fotoluminescência, varistores e mais recentemente em sensores de gás. Estas múltiplas aplicações fazem com que este material seja de grande interesse científico e tecnológico. Portanto, o objetivo deste trabalho foi estudar sistemas cerâmicos com fórmula estequiométrica CaCu3-xSrxTi4O12 sendo x = 0,00; 0,15; 0,30 e 3,00; na forma de pó e bulk, preparados por reação em estado sólido, assim como na forma de filmes depositados por RF-sputtering. A partir da difratometria de raios X e refinamento Rietveld dos pós encontrou-se que a amostra com x = 0,00 apresentaram a fase CCTO, e amostras com x = 3,00 a fase Sr0,75Ca0,25TiO3 (SCTO), cuja estrutura é ortorrômbica com grupo espacial Ibmm coeficiente de ajuste (χ2) e fator de estrutura do refinamento Rietveld próximos aos relatados pela literatura. Os pós com x = 0,15 e x = 0,30 apresentaram mistura das fases CCTO, CTO e SCTO. A resposta fotoluminescente mostrou emissão na região azul para as amostras na forma de pós com x =0,00, associada a defeitos profundos dentro do band-gap, a introdução de Sr2+ levou a emissão na região do amarelo- laranja-vermelho, produto de aumento de defeitos rasos e também levou a diminuição no tamanho de partícula, em parte responsável da diminuição na emissão no verde. Espectroscopia Raman foi usada para auxiliar na interpretação da resposta fotoluminescente. Nas cerâmicas na forma de bulk também foi estudada a estrutura cristalina com ajuda do refinamento Rietveld nestas houve combinações das fases CCTO e SCTO em diferentes RESUMO vi proporções com pequenas alterações na estequiometria. A microscopia eletrônica de varredura mostrou que a amostra com x = 0,15 apresentou um significativo crescimento de grão, o qual contribuiu para a elevada constante dielétrica (327979). A diminuição da perda dielétrica obtida para amostras com x = 3,00 foi produto do crescimento da resistência do contorno de grão conforme simulação de circuitos elétricos, este aumento na resistência do contorno de grão fez este sistema apresentar baixa corrente de fuga (81µA) e um coeficiente de não linearidade α=10. Por outro lado, os filmes finos densos mostraram permissividade dielétrica (10), equivalente as relatadas por outros autores com filmes de espessura maior e com baixas perdas dielétricas. A resposta sensora dos filmes porosos mostrou um melhor sinal para o filme preparado com o alvo de x = 0,15. Os filmes foram mais seletivos para o CO. O filme de CCTO (x= 0,00) apresentou um comportamento tipo-n, e o de SCTO (x = 0,15) comportamento tipo p. Os tempos de resposta e de recuperação foram próximos aos de sensores comerciais, porém, estes incrementaram com o número de ciclos realizados.
The ceramic systems based on CaCu3Ti4O12 (CCTO) have high potential for various technological applications such as: capacitors, resistive memories, photoluminescence, varistors and more recently in gas sensors. These multiple applications make this material of great scientific and technological interest. Therefore, the objective of this work was to study ceramic systems with stoichiometric formula CaCu3-xSrxTi4O12 where x = 0.00; 0.15; 0.30 and 3.00; in the form of powder and bulk, prepared by reaction in solid state, as well as in the form of films deposited by RF-sputtering. From the X-ray diffraction powder and Rietveld refinement we found that the sample with x = 0.00 presented the CCTO phase, and samples with x = 3.00 the Sr0.75Ca0.25TiO3 (SCTO) phase, whose structure is orthorhombic with spatial group Ibmm adjustment coefficient (χ 2 ) and Rietveld refinement structure factor close to those reported in the literature. The powders with x = 0.15 and x = 0.30 showed a mixture of the CCTO, CTO and SCTO phases. The photoluminescent response showed emission in the blue region for the samples in the form of powders with x = 0.00, associated with deep defects within the band gap, the introduction of Sr2+ led to the emission in the region of yellow-orange-red, product of increase in shallow defects and also led to decrease in particle size, partly responsible for the decrease in emission in green. Raman spectroscopy was used to aid in the interpretation of the photoluminescent response. In the ceramics in the form of bulk also the crystal structure was studied with the help of the Rietveld refinement in these there were combinations of the ABSTRACT viii CCTO and SCTO phases in different proportions with small changes in the stoichiometry. Scanning electron microscopy showed that the sample with x = 0.15 showed a significant grain growth, which contributed to the high dielectric constant (327979). The reduction of the dielectric loss obtained for samples with x = 3.00 resulted from the growth of the grain boundary resistance as simulated by electric circuits, this increase in grain boundary strength caused the system to have a low leakage current (81μA) and a coefficient of non-linearity α = 10. On the other hand, dense thin films showed dielectric permissiveness (10), equivalent to those reported by other authors with films of higher thickness and with low dielectric losses. The sen09oip-0000, .sory response of the porous films showed a better signal for the film prepared with the target of x = 0.15. The films were more selective for the CO. The CCTO film (x = 0.00) presented a n-type behavior, and that of SCTO (x = 0.15) p-type behavior. Response and recovery times were close to those of commercial sensors, however, these increased with the number of cycles performed
The ceramic systems based on CaCu3Ti4O12 (CCTO) have high potential for various technological applications such as: capacitors, resistive memories, photoluminescence, varistors and more recently in gas sensors. These multiple applications make this material of great scientific and technological interest. Therefore, the objective of this work was to study ceramic systems with stoichiometric formula CaCu3-xSrxTi4O12 where x = 0.00; 0.15; 0.30 and 3.00; in the form of powder and bulk, prepared by reaction in solid state, as well as in the form of films deposited by RF-sputtering. From the X-ray diffraction powder and Rietveld refinement we found that the sample with x = 0.00 presented the CCTO phase, and samples with x = 3.00 the Sr0.75Ca0.25TiO3 (SCTO) phase, whose structure is orthorhombic with spatial group Ibmm adjustment coefficient (χ 2 ) and Rietveld refinement structure factor close to those reported in the literature. The powders with x = 0.15 and x = 0.30 showed a mixture of the CCTO, CTO and SCTO phases. The photoluminescent response showed emission in the blue region for the samples in the form of powders with x = 0.00, associated with deep defects within the band gap, the introduction of Sr2+ led to the emission in the region of yellow-orange-red, product of increase in shallow defects and also led to decrease in particle size, partly responsible for the decrease in emission in green. Raman spectroscopy was used to aid in the interpretation of the photoluminescent response. In the ceramics in the form of bulk also the crystal structure was studied with the help of the Rietveld refinement in these there were combinations of the ABSTRACT viii CCTO and SCTO phases in different proportions with small changes in the stoichiometry. Scanning electron microscopy showed that the sample with x = 0.15 showed a significant grain growth, which contributed to the high dielectric constant (327979). The reduction of the dielectric loss obtained for samples with x = 3.00 resulted from the growth of the grain boundary resistance as simulated by electric circuits, this increase in grain boundary strength caused the system to have a low leakage current (81μA) and a coefficient of non-linearity α = 10. On the other hand, dense thin films showed dielectric permissiveness (10), equivalent to those reported by other authors with films of higher thickness and with low dielectric losses. The sen09oip-0000, .sory response of the porous films showed a better signal for the film prepared with the target of x = 0.15. The films were more selective for the CO. The CCTO film (x = 0.00) presented a n-type behavior, and that of SCTO (x = 0.15) p-type behavior. Response and recovery times were close to those of commercial sensors, however, these increased with the number of cycles performed
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Palavras-chave
CCTO, SCTO, Filmes finos, Refinamento Rietveld, Sensor de gás, Thin films, Rietveld refinement, Gas sense