Preparação de filmes finos ferroelétricos de SrBi2'('TA IND.1-x''NB IND.x)ÍND.2 'O IND.9' puro e dopado com tungstênio, obtidos pelo método dos precursores poliméricos
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2007-04-23
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Universidade Estadual Paulista (Unesp)
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Neste trabalho, filmes finos de SrBi2(Ta1-xNbx)2O9 (SBTN) puros e modificados com tungstênio foram preparados através do método dos precursores poliméricos. Os reagentes básicos utilizados na preparação foram: complexo amoniacal de nióbio, carbonato de estrôncio, óxido de bismuto, etóxido de tântalo e óxido de tunstênio. O ácido cítrico foi utilizado como agente complexante e o etilenoglicol e etilenodiamina como agente polimerizante. Os filmes foram depositados sobre substrato de Pt/Ti/SiO2/Si(100). As propriedades estruturais e microestruturais foram avaliadas por difratometria de raios-X (DRX), microscopia de força atômica (MFA) e microscopia eletrônica de varredura (MEV). Loops de histerese foram obtidos para avaliar as propriedades ferroelétricas. As propriedades dielétricas foram determinadas através das medidas de capacitância em função da frequência. DRX dos pós de SBTN mostraram que a fase perovisquita forma a uma temperatura acima de 600 ?C e que abaixo desta temperatura existe uma fase secundária tipo fluorita. O refinamento pelo método de Rietveld indicou uma estrutura ortorrômbica com grupo espacial 2A1ma. Os filmes cristalizados segundo a rota de cristalização intermediária amorfa mostrou-se mais promissora aos obtidos pela rota de cristalização intermediária cristalina. A razão Ta/Nb foi avaliada no sistema SBTN onde foi observado grãos menores com adição de tântalo. Os filmes multicamadas apresentaram uma microstrutura densa, livres de trincas e com tamanho médio de grãos da ordem de 100 nm. A adição de tungstênio no sistema SBTN melhorou as propriedades ferroelétricas. Filmes mofidicados com 2,0 mol% de tungstênio mostrou polarização remanescente e campo coercitivo de 8,0 ?C/cm2 e 165 kV/cm, respectivamente e constante dielétrica e fator de dissipação de 114 e 0,03, respectivamente.
In this work, pure and tungsten doped SrBi2(Ta1-xNbx)2O9 (SBTN) thin films and powders were synthesized by the polymeric precursor method. Niobium ammonium complex, strontium carbonate, tantalum ethoxide, tungsten oxide and bismuth oxide were used as cation sources. Citric acid was used as complexing agent and ethylene glycol and ethylenediamine as polymerization agent. The films were deposited successfully on Pt/Ti/SiO2/Si(100) substrates by spin-coating technique. The structural and microstructural properties of the films were characterized by X-Ray Diffraction (XRD), Atomic Force Microscopy (AFM) and Scanning Electronic Microscopy (SEM) techniques. Histeresis loops were obtained to evaluate the ferroelectric properties. The dielectric properties were evaluated by capacitance analyses as function of frequency. XRD analysis of the SBTN powders showed that perovskite phase forms at temperature as low as 600 ?C through an intermediate fluorite phase. Rietveld refinement indicated an orthorhombic structure with 2A1ma space group. the films crystallized by intermediate amorphous route is more promising than intermediate crystalline route. Ta/Nb ratio were evaluated in the SBTN thin films and showed decrease of grain size when tantalum was added. The multilayered films presented a dense and crack free with spherical grains around 100 nm. Tungsten addition in the SBTN system improved the ferroelectric properties. 2.0 mol% in W6+ in the SBTN thin film showed remanent polarization and coercive field values of 8.0 ?C/cm2 and 165 kV/cm, respectively and dielectric constant and dissipation factor values of 114 and 0.030, respectively. Tungsten doped SBTN thin films were annealing at 700 ?C in oxygen atmosphere to improve the ferroelectric properties. The films showed good ferroelectric and dielectric properties. The remanent polarization and coercive field values of 8.2?C/cm2 and 85 kV/cm, respectively, were found for the 2.0 %mol tungsten doped SBTN film
In this work, pure and tungsten doped SrBi2(Ta1-xNbx)2O9 (SBTN) thin films and powders were synthesized by the polymeric precursor method. Niobium ammonium complex, strontium carbonate, tantalum ethoxide, tungsten oxide and bismuth oxide were used as cation sources. Citric acid was used as complexing agent and ethylene glycol and ethylenediamine as polymerization agent. The films were deposited successfully on Pt/Ti/SiO2/Si(100) substrates by spin-coating technique. The structural and microstructural properties of the films were characterized by X-Ray Diffraction (XRD), Atomic Force Microscopy (AFM) and Scanning Electronic Microscopy (SEM) techniques. Histeresis loops were obtained to evaluate the ferroelectric properties. The dielectric properties were evaluated by capacitance analyses as function of frequency. XRD analysis of the SBTN powders showed that perovskite phase forms at temperature as low as 600 ?C through an intermediate fluorite phase. Rietveld refinement indicated an orthorhombic structure with 2A1ma space group. the films crystallized by intermediate amorphous route is more promising than intermediate crystalline route. Ta/Nb ratio were evaluated in the SBTN thin films and showed decrease of grain size when tantalum was added. The multilayered films presented a dense and crack free with spherical grains around 100 nm. Tungsten addition in the SBTN system improved the ferroelectric properties. 2.0 mol% in W6+ in the SBTN thin film showed remanent polarization and coercive field values of 8.0 ?C/cm2 and 165 kV/cm, respectively and dielectric constant and dissipation factor values of 114 and 0.030, respectively. Tungsten doped SBTN thin films were annealing at 700 ?C in oxygen atmosphere to improve the ferroelectric properties. The films showed good ferroelectric and dielectric properties. The remanent polarization and coercive field values of 8.2?C/cm2 and 85 kV/cm, respectively, were found for the 2.0 %mol tungsten doped SBTN film
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Filmes finos - Materiais, Precursores poliméricos, Ferroelétrico
Como citar
AMSEI JÚNIOR, Norberto Luiz. Preparação de filmes finos ferroelétricos de SrBi2'('TA IND.1-x''NB IND.x)ÍND.2 'O IND.9' puro e dopado com tungstênio, obtidos pelo método dos precursores poliméricos. 2007. 103 f. Tese (doutorado) - Universidade Estadual Paulista, Instituto de Química., 2007.