Filmes finos ferroelétricos do tipo PBCT, PBST e PCST: estudo experimental e teórico
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Data
2012-02-24
Autores
Pontes, Debora da Silva Lima [UNESP]
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
Perovisquita é a estrutura mais comum vista nos materiais ferroelétricos, a qual tem sido amplamente utilizado na indústria de dispositivos nas últimas décadas. Dentre essa classe de materiais o PbTiO3 é um dos materiais extensamente estudado devido a sua ampla faixa de aplicações como, por exemplo, capacitores, sensores piroelétrico e piezelétricos, memórias ferroelétricas. A substituição do Pb2+ pelos íons Ba2+/Ca2+, Ba2+/Sr2+ e Ca2+/Sr2+ no siste ma PbtiO3, a qual conduziu a formação de sistemas PBCT, PBST e PCST, produziu varias mudanças nas propriedades elétricas e estruturais desses materiais. No entanto, poucos trabalhos têm sido dedicados a esses sistemas baseado numa incorporação complexa de dois diferentes íons no sítio A, com relação a um profundo estudo teórico e experimental. A caracterização experimental por difração de raios X, espectroscopia micro-Raman e FT-IR mostram uma diminuição no grau de tetragonalidade para esses materiais. Essa alteração estrutural em função dos substituintes foi também responsável pela diminuição do grau de polarização. Nesta tese, foi aplicado também o método computacional dos primeiros princípios para estudar esta importante classe de materiais. A estrutura eletrônica, energia do banc gap, a densidade e estados (DOS) nos cristais ferroelétricos PBCT, PBST e PCST foram estudadas usando a teoria do funcional de densidade combinada com B3LYP. Os resultados teóricos foram correlacionados com os resultados experimentais para investigar e interpretar melhor a influência dos pares de íons Ba/Ca, Ba/Sr e Ca/Sr na ferroeletricidade do sistema PT. Pela análise teórica o grau de polarização bem como de tetragonalidade diminuiu no sistema PCST comparado ao PBCT e PBST, devido à presença agora de um forte caráter de ligações iônicas dentro...
Perovskites are the most commonly seen ferroelectrics, which have been widely used in the industry of devices in the last few decades. In addition, Lead titanate (PbTiO3) is an extensively studied material wich a wide range of application, for intance as capacitors, piezoeletric and pyroelectric sensors and ferroelectric memories. The substitution of Pb2+ ions Ba2+/Ca2+, Ba2+/Sr2+ e Ca2+/Sr2+ ions in the PbTiO3 system, which leads to the formation of the PBCT, PBST e PCST systems, induces several change in the electric and structural properties of these materials. However, PBCT, PBST and PCST systems based on the complex incorporation of two different ions at site A have not been thoroughly investigated and the literature contains few reports concerning their experimental and theoretical study of these materials. The characterization with X-ray diffraction, Raman spectroscopy and spectroscopy techniques on the infrared region of these samples showed a decrease of the tetragonality degree. These structural modifications were also responsible by the decrease in the polarization degree of these samples. In this thesis, we also have applied first-principles computational methods to the study this important class of materials. The electronic structure, energy band structure, and density of states (DOS) in ferroelectric crystal PBCT and PCST are studied by using density functional theory (DFT) combined with the B3LYP. The theoretical results were correlated with experimentals results to investigate and interpret better the influence of pairs of ions Ba/Ca, Ba/Sr and Ca/Sr on the ferroelectricity of the system PT. By theoretical analysis the degree of polarization as well as ferroelectricity in the PCST decreased compared with the systems PBCT and PBST, due to the presence of strong ionic character in this crystal... (Complete abstract click electronic access below)
Perovskites are the most commonly seen ferroelectrics, which have been widely used in the industry of devices in the last few decades. In addition, Lead titanate (PbTiO3) is an extensively studied material wich a wide range of application, for intance as capacitors, piezoeletric and pyroelectric sensors and ferroelectric memories. The substitution of Pb2+ ions Ba2+/Ca2+, Ba2+/Sr2+ e Ca2+/Sr2+ ions in the PbTiO3 system, which leads to the formation of the PBCT, PBST e PCST systems, induces several change in the electric and structural properties of these materials. However, PBCT, PBST and PCST systems based on the complex incorporation of two different ions at site A have not been thoroughly investigated and the literature contains few reports concerning their experimental and theoretical study of these materials. The characterization with X-ray diffraction, Raman spectroscopy and spectroscopy techniques on the infrared region of these samples showed a decrease of the tetragonality degree. These structural modifications were also responsible by the decrease in the polarization degree of these samples. In this thesis, we also have applied first-principles computational methods to the study this important class of materials. The electronic structure, energy band structure, and density of states (DOS) in ferroelectric crystal PBCT and PCST are studied by using density functional theory (DFT) combined with the B3LYP. The theoretical results were correlated with experimentals results to investigate and interpret better the influence of pairs of ions Ba/Ca, Ba/Sr and Ca/Sr on the ferroelectricity of the system PT. By theoretical analysis the degree of polarization as well as ferroelectricity in the PCST decreased compared with the systems PBCT and PBST, due to the presence of strong ionic character in this crystal... (Complete abstract click electronic access below)
Descrição
Palavras-chave
Dispositivos ferroelétricos, Filmes finos, Piezoelectric devices, Thin films
Como citar
PONTES, Debora da Silva Lima. Filmes finos ferroelétricos do tipo PBCT, PBST e PCST: estudo experimental e teórico. 2012. 140 f. Tese (doutorado) - Universidade Estadual Paulista, Faculdade de Ciências, 2012.