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Oliveira R.G.M.,Caixa Postal 6007 | Romeu M.C.,Caixa Postal 6007 | Costa M.M.,Laboratorio Of Telecomunicacoes | Costa M.M.,Federal University of Mato Grosso | And 5 more authors.
Journal of Alloys and Compounds | Year: 2014

The effects of different additions of Bi2O3 (0, 2, 5 and 10 wt.%) on Na2Nb4O11 ceramics have been studied by complex impedance spectroscopy analysis. The structural and dielectric properties of Na2Nb4O11ceramics with Bi2O3 additions are also discussed as a possible material for microwave and radio frequency applications. Solid state reaction method was used for producing the target compound. The present work also reports on sample preparation, where polyvinyl alcohol was used as a binder to reduce the brittleness and the organic binder was burnt out during sintering process. X-ray diffraction at room temperature was used to identify phases formed as well as optimum calcinations conditions the production of Na2Nb 4O11 powder. Analysis was carried out to identify the pure-phase specimen by Rietveld refinement method. Based on this method a structure with the lattice parameters (a = 10.840 Å, b = 6.162 Å and c = 12.745 Å; α = 90, β = 106.4 and γ = 90) was found. The dielectric and electrical properties of Na2Nb4O 11 for appropriate amounts of Bi2O3 additions has showed a considerable enhancement and overriding applications for microwave and radio frequency communications. The electrical behavior (complex impedance Z*, complex modulus M*) were studied over a frequency range (1 Hz to 1 MHz) and temperature (553-713 K). © 2013 Elsevier B.V. All rights reserved.


Romeu M.C.,Federal University of Ceará | Romeu M.C.,Laboratorio Of Telecomunicacoes | Oliveira R.G.M.,Federal University of Ceará | Oliveira R.G.M.,Laboratorio Of Telecomunicacoes | And 9 more authors.
Journal of Materials Science: Materials in Electronics | Year: 2013

In this paper a study of TiO2 addition (0, 2, 5 and 10 wt%) and its effects in the impedance spectra of Na2Nb4O 11 ceramic matrix was carried out. The structural, dielectric properties of the addition in the Na2Nb4O11 matrix were discussed. In the preliminary structural studies, X-ray diffractograms of the samples were recorded at room temperature with X-ray diffractometer with Cu-kα. The Rietveld refinement method was used and confirmed the monoclinic structure for pure sample. A study based on complex impedance spectroscopy was carried and the dielectric properties were obtained over a frequency range (100 Hz-1 MHz) in room temperature (300 K). In the dielectric analysis at 1 MHz was observed relative permittivity of 99.46 for pure sample and 84.37 to sample added with 5 wt% of TiO2, those samples showed losses 3.55 × 10-2 and 9.22 × 10 -2, respectively. In relation to relaxation phenomenon, Cole-Cole function was used for fitting pure and added samples data. © 2013 Springer Science+Business Media New York.

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