Estudo da correlação entre propriedades não-ôhmicas, processos de relaxação dielétrica e microestrutura de cerâmicas policristalinas do tipo (Ca IND. 1/4 Cu IND. 3/4)TiO IND. 3
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Data
2010-02-12
Autores
Ribeiro, Willian Campos [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Neste trabalho buscou-se estabelecer uma correlação entre as propriedades nãoôhmicas e dielétricas do CaCu3Ti4O12 (CCTO) considerando a influência da microestrutura obtida pela variação do tempo de sinterização (3, 12, 24, 48 ou 72 h). Em virtude dos modelos descritos na literatura não contemplarem todas as características elétricas apresentadas pelo CCTO, um modelo chamado NBLC (Nanosized Barrier Layer Capacitor) foi delineado, discutido e aplicado sobre os resultados obtidos. Além disso, a adição de SnO2 no CCTO foi realizada para validar o modelo NBLC. As medidas de difração de raios-X (DRX) e microscopia eletrônica de varredura (MEV) mostraram que as medidas elétricas não possuem relação com a formação de precipitados ou fase secundária dentro do limite das técnicas. A diminuição do campo elétrico de ruptura r E e do coeficiente de não linearidade a , além do aumento da corrente de fuga f I , exibiram a degradação da propriedade não-ôhmica com o aumento do tempo de sinterização que foram relatados a dessorção de oxigênio. Como consequência, as resistências do grão e do contorno de grão diminuíram, assim como a quantidade de cargas no contorno de grão. Para verificar a origem da constante dielétrica, foram analisados os processos de relaxação dielétrica e condutiva que apresentaram 3 processos: cargas espaciais no contorno de grão (baixa frequência), cargas espaciais nas nanobarreiras capacitivas (frequência intermediária) e polarização hopping de polarons (alta frequência). A energia de ativação para o fenômeno em alta frequência foi calculada, indicando a presença de polarons na estrutura. Para estabelecer a relação entre tempo de sinterização e quantidade de defeitos no material, medidas de colorimetria foram efetuadas. O modelo NBLC conciliou a elevada constante dielétrica com baixa resistência que, a princípio...
The goal of this work was established a correlation between non-ohmic and dielectric behavior in CaCu3Ti4O12 (CCTO) polycrystalline ceramics in that was verified the influence of microstructure obtained in several sintering time (3, 12, 24, 48 or 72 h). The NBLC model (Nanosized Barrier Layer Capacitor) was described and applied over the results obtained here. This model showed to be better than the literature models because can join high dielectric constant and low resistivity. The CCTO ceramics was doping by SnO2 to valid NBLC model. X-ray diffraction (XRD) and scanning electronic microscopy (SEM) measurements showed that secondary phase or precipitated has no relation with electrical behavior. Switch electric field r E and nonlinear coefficient a increased while leakage current f I diminished function of sintering time. These facts were related of oxygen desorption and as a consequence the grain and grain boundary resistivity decreased. The origin of dielectric behavior was discussed based on relaxation process amount, obtained 3 processes: space charge in grain boundary (low frequency), space charge in nanosized barriers (medium frequency) and hopping polarization of polaron (high frequency). Activation energy of the high frequency phenomenon was a clue of polaron existence. To establish a relationship between sintering time and defect amount in the material, colorimetric measurements were carried out. The incoherencies of CCTO electrical features present in the literature were explained by NBLC model. The SnO2 doping CCTO was carried out to support NBLC model. Thus, the non-ohmic property improved when no stacking faults had. The grain and grain boundary resistivity increased and dielectric constant diminished two fold orders. The defect amount control is important to point the better application: high frequency dielectric or varistor device
The goal of this work was established a correlation between non-ohmic and dielectric behavior in CaCu3Ti4O12 (CCTO) polycrystalline ceramics in that was verified the influence of microstructure obtained in several sintering time (3, 12, 24, 48 or 72 h). The NBLC model (Nanosized Barrier Layer Capacitor) was described and applied over the results obtained here. This model showed to be better than the literature models because can join high dielectric constant and low resistivity. The CCTO ceramics was doping by SnO2 to valid NBLC model. X-ray diffraction (XRD) and scanning electronic microscopy (SEM) measurements showed that secondary phase or precipitated has no relation with electrical behavior. Switch electric field r E and nonlinear coefficient a increased while leakage current f I diminished function of sintering time. These facts were related of oxygen desorption and as a consequence the grain and grain boundary resistivity decreased. The origin of dielectric behavior was discussed based on relaxation process amount, obtained 3 processes: space charge in grain boundary (low frequency), space charge in nanosized barriers (medium frequency) and hopping polarization of polaron (high frequency). Activation energy of the high frequency phenomenon was a clue of polaron existence. To establish a relationship between sintering time and defect amount in the material, colorimetric measurements were carried out. The incoherencies of CCTO electrical features present in the literature were explained by NBLC model. The SnO2 doping CCTO was carried out to support NBLC model. Thus, the non-ohmic property improved when no stacking faults had. The grain and grain boundary resistivity increased and dielectric constant diminished two fold orders. The defect amount control is important to point the better application: high frequency dielectric or varistor device
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Físico-química, Dieletricos, Varistores, Physical chemistry, Dielectrics
Como citar
RIBEIRO, Willian Campos. Estudo da correlação entre propriedades não-ôhmicas, processos de relaxação dielétrica e microestrutura de cerâmicas policristalinas do tipo (Ca IND. 1/4 Cu IND. 3/4)TiO IND. 3. 2010. 103 f. Dissertação (mestrado) - Universidade Estadual Paulista, Instituto de Química, 2010.