Estudos de materiais ferroelétricos por espectroscopia no infravermelho

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Transições de fases estruturais do sistema PZT, estudados por espectroscopia no infravermelho

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Obtenção de niobato de chumbo e zinco (PZN) com fase e microestrutura controladas

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Filmes finos ferroelétricos do tipo PBCT, PBST e PCST: estudo experimental e teórico

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Modelagem computacional de óxidos da família das perovskitas

Pós-graduação em Ciência e Tecnologia de Materiais - FC

Influence of a co-substituted A-site on structural characteristics and ferroelectricity of (Pb, Ba, Ca)TiO3 complex perovskites: analysis of local-, medium- and long-range order

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Titanium K-edge XAS study on local structure of Pb1-xCaxTiO3 ferroelectric ceramics

In order to characterize the local structure of Pb1-xCaxTiO3 (PCT) samples, Ti K-edge XANES measurements were performed and showed that Ca incorporation to PbTiO3 structure leads to a decreasing of local distortion of Ti atoms in relation to oxygen atoms at the TiO6 octahedra. Moreover, according to EXAFS measurements, the local structure around Ti atoms exhibits tetragonal symmetry with P4mm space group for samples with x <= 0.475, whereas orthorhombic symmetry with Pbnm space group was observed for x equals to 0.50 and 0.55.

Local structure around Fe ions on multiferroic Pb(Fe1/2Nb1/2)O-3 ceramics probed by x-ray absorption spectroscopy

Local structure around Fe ions on Pb(Fe1/2Nb1/2)O-3 ceramics was probed by x-ray absorption spectroscopy in order to settle the controversies about its structure. It is observed that the shell structure around Fe atoms exhibits a monoclinic local symmetry at 130 and 230 K, tetragonal local symmetry at room temperature, and cubic local symmetry at 410 K. Independently of the coordination, temperature, or symmetry, Fe-O mean bond-length does not vary significantly. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4709490]

Grain size effect on the structural and dielectric properties of Pb0.85La0.15TiO3 ferroelectric ceramic compound

This paper presents a study of the influence of particle size on the structural and dielectric properties of Pb0.85La0.15TiO3 (PLT15) ferroelectric ceramic samples. The samples were prepared with average grain size of 1.69 +/- 0.08 mu m and 146 +/- 8 nm using, respectively, conventional and spark plasma sintering techniques. A decrease in the tetragonality degree as the crystallite size decreased was explained by an internal stress caused by the existence of a large amount of grain boundaries. The local structure exhibited no significant modification and the dielectric measurements showed a diffuse phase transition and a reduction in the permittivity magnitude at T-m as the average grain size decreased. The nanostructured ceramic sample prepared at a relatively lower temperature and sintering time presented a dielectric constant value of approximately 2000 at room temperature. (c) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Pb0.90Ba0.10Zr0.40Ti0.60O3 Nanostructured Ferroelectric Ceramics Prepared by Spark Plasma Sintering

Nanostructured Pb0.90Ba0.10Zr0.40Ti0.60O3 dense ceramics presenting an average grain size of 62 +/- 5 nm was prepared by the polymeric precursor method and using the spark plasma sintering technique. The dielectric permittivity curves versus temperature exhibit broad anomaly, indicative of a diffuse phase transition. This result can be explained by the spread of Curie temperatures which are expected to depend on the degree of tetragonality related to the grain size distribution. A pronounced decrease in the maximum of the dielectric permittivity value is attributed to the existence of a large amount of grain boundaries which are non-ferroelectric regions.

Influence of Ba-substitution on the structural and ferroelectric properties of Pb1-xBaxZr0.40Ti0.60O3 ceramic materials

This work presents a comprehensive study about the influence of Ba-substitution on the structural and ferroelectric properties of Pb1-xBaxZr0.40Ti0.60O3 (PBZT) ceramic system. Pb1-xBaxZr0.40Ti0.60O3 ceramic samples were then prepared by solid state reaction method and characterized as a function of composition and temperature by X-ray diffraction (XRD) and impedance spectroscopy techniques. The dielectric measurements show that the substitution of Pb2+ for Ba2+ ions leads to a diffuse behavior of the dielectric permittivity curves for all samples and that only the x = 0.50 sample presents a typical relaxor behavior. In good agreement with dielectric measurements, the structural phase transition study showed a phase transition from a tetragonal structure with P4mm space group to a cubic structure with Pm-3m space group for all samples, except for the x = 0.50 sample were a cubic structure was observed in the complete temperature interval measured.