Estudo de transições de fases estruturais nos sistemas PZT e PMN-PT por espectroscopia no infravermelho e espectroscopia de impedância
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Data
2009-04-17
Autores
Guarany, Cristiano Alves [UNESP]
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
O Sistema ferroelétrico Pb'Z IND. 1-x''Ti IND. x''O IND. 3'(PZT) vem sendo amplamente estudado devido a interessantes propriedades físicas para composições próximas ao contorno de fase morfotrópico (CFM). No PZT o CFM se encontra em composições próximas a x = 0,50 no diagrama de fases, e separa a fase tetragonal da monoclínica. Nesta região é onde o PZT exibe elevado coeficiente eletromecânico. Comportamento e características similares também são exibidos no sistema 'Pb('Mg IND. 1/3''Nb IND. 2/3''O IND. 3) IND. (1-x)'Ti IND. x''O IND. 3' (PMN-PT), com propriedades eletromecânicas uma ordem de magnitude superior ao das cerâmicas de PZT. Desde a descoberta de uma fase ferroelétrica monoclínica nas proximidades do CFM para sistemas PZT e PMN-PT, estes ferroelétricos vem atraindo a atenção de diversos pesquisadores na tentativa de compreender a relação entre as características estruturais e as propriedades piezelétricas. Além disso, a descoberta de uma transição de fase estrutural induzida pela aplicação de um campo elétrico externo no PMN-PT realça o importante papel da fase intermediária monoclínica na alta resposta eletromecânica destes materiais. Nesta tese, transições de fases estruturais nos sistemas PZT e PMN-PT foram investigadas utilizando a técnica de espectroscopia de infravermelho em função da temperatura. Os estudos em função da temperatura foram centrados nos modos 'v IND. 1'-stretching, dos octaedros 'BO IND. 6' na estrutura 'AB IND. 3', e nas correspondentes larguras a meia altura 'W IND. i' para os sistemas PZT e PMN-PT. A ocorrência de anomalias no modo 'v IND. 1'-stretching foi associada à transição de fase estrutural. Um estudo suplementar, da influência de campos elétricos contínuos e alternados, nas propriedades dielétricas em função da temperatura para cerâmicas de PMN-35PT foi conduzido utilizando espectroscopia de impedância.
The Pb'Z IND. 1-x''Ti IND. x''O IND. 3'(PZT) ferroelectric system has been extensively studied because of its interesting physical proprieties close to the morphotropic phase boundary (MPB), the nearly vertical phase boundary between the tretragonal and monoclinic regions of the phase diagram to x = 0.50, where the material exhibits outstanding electromechanical proprieties. Similar behavior and features are also present in 'Pb('Mg IND. 1/3''Nb IND. 2/3''O IND. 3) IND. (1-x)'Ti IND. x''O IND. 3' (PMN-PT), with electromechanical proprieties sometimes one order of magnitude large than PZT ceramics. Since the discovery of a ferroelectric monoclinic phase in the PZT and PMN-PT system, for composition close to MPB that was not predicted on the original phase diagram, these ferroelectrics attained the attention of several researches due to the possibility of understanding the relatonship between structural features and piezoelectric properties. Moreover, interesting electric field induced phase transitions were discovered in PMN-PT highlighting the important role of the intermediate monoclinic phase for high electromechanical response of this material. In this thesis, structural phase transition was PZT and PMN-PT system were investigated by infrared spectroscopy as a function of temperature. Studies were centered on monitoring the behavior of the 'v IND. 1'-stretching modes and corresponding half width 'W IND. i' as a function of temperature in 'BO IND. 6' octahedron in 'AB IND. 3' structure of the PZT and PMN-PT. The occurrences of the anomalies in the 'v IND. 1'-stretching modes were associated to a structural phase transition. Additional temperature dependence of dielectric properties for PMN-0.35PT ceramics under different dc bias and ac driving electric fields were investigated by impedance spectroscopy.
The Pb'Z IND. 1-x''Ti IND. x''O IND. 3'(PZT) ferroelectric system has been extensively studied because of its interesting physical proprieties close to the morphotropic phase boundary (MPB), the nearly vertical phase boundary between the tretragonal and monoclinic regions of the phase diagram to x = 0.50, where the material exhibits outstanding electromechanical proprieties. Similar behavior and features are also present in 'Pb('Mg IND. 1/3''Nb IND. 2/3''O IND. 3) IND. (1-x)'Ti IND. x''O IND. 3' (PMN-PT), with electromechanical proprieties sometimes one order of magnitude large than PZT ceramics. Since the discovery of a ferroelectric monoclinic phase in the PZT and PMN-PT system, for composition close to MPB that was not predicted on the original phase diagram, these ferroelectrics attained the attention of several researches due to the possibility of understanding the relatonship between structural features and piezoelectric properties. Moreover, interesting electric field induced phase transitions were discovered in PMN-PT highlighting the important role of the intermediate monoclinic phase for high electromechanical response of this material. In this thesis, structural phase transition was PZT and PMN-PT system were investigated by infrared spectroscopy as a function of temperature. Studies were centered on monitoring the behavior of the 'v IND. 1'-stretching modes and corresponding half width 'W IND. i' as a function of temperature in 'BO IND. 6' octahedron in 'AB IND. 3' structure of the PZT and PMN-PT. The occurrences of the anomalies in the 'v IND. 1'-stretching modes were associated to a structural phase transition. Additional temperature dependence of dielectric properties for PMN-0.35PT ceramics under different dc bias and ac driving electric fields were investigated by impedance spectroscopy.
Descrição
Palavras-chave
Ciencia, Ferroelétricos, Ferroelectric
Como citar
GUARANY, Cristiano Alves. Estudo de transições de fases estruturais nos sistemas PZT e PMN-PT por espectroscopia no infravermelho e espectroscopia de impedância. 2009. 150 f. Tese (doutorado) - Universidade Estadual Paulista, Faculdade de Ciências de Bauru, 2009.