• JoomlaWorks Simple Image Rotator
  • JoomlaWorks Simple Image Rotator
  • JoomlaWorks Simple Image Rotator
  • JoomlaWorks Simple Image Rotator
  • JoomlaWorks Simple Image Rotator
  • JoomlaWorks Simple Image Rotator
  • JoomlaWorks Simple Image Rotator
  • JoomlaWorks Simple Image Rotator
  • JoomlaWorks Simple Image Rotator
  • JoomlaWorks Simple Image Rotator
 
  Bookmark and Share
 
 
Doctoral Thesis
DOI
10.11606/T.54.1991.tde-02042015-151449
Document
Author
Full name
Guillermo Guzman Martel
Institute/School/College
Knowledge Area
Date of Defense
Published
São Carlos, 1991
Supervisor
Committee
Aegerter, Michel Andre (President)
Andreeta, Jose Pedro
Campos, Milton Soares de
Casarini, Jose Roberto
Souza, Dulcina Maria Pinatti Ferreira de
Title in Portuguese
Síntese e caracterização de cerâmicas ferroelétricas Pb (Mg1Nb2/3)O3
Keywords in Portuguese
Não disponível
Abstract in Portuguese
Neste trabalho foram estudadas as propriedades dielétricas do relaxador ferroelétrico Pb (Mg1Nb2/3)O3. O pó PMN puro foi preparado por métodos clássicos (moagem e calcinação) e por coprecipitação em solução aquosa. A reatividade do magnésio, que influi no aparecimento da fase pirocloro deletérea Pb3Nb4O13, foi estudada usando óxidos , carbonatos e nitratos. A reatividade do Chumbo também foi estudada usando as duas formas halotrópicas do PbO. Foi observada a influência da distribuição do tamanho de partículas dos óxidos de chumbo e de nióbio na formação do PMN. O PMN quase-puro foi preparado com o uso de nitrato de magnésio, óxido de chumbo tipo ortorrômbico e óxido de nióbio, estes dois últimos, com tamanho médio de partículas de 2,5μm e 1μm respectivamente. A sinterização do PMN foi realizada a 950°C durante 4h. Aditivos tais como 4% PbO e 2%MgO são fundamentais para se obter cerâmicas PMN com densidade aparente þ > 0,9 þ teórico. Estudou-se também a dependência da constante dielétrica em função da proporção de fase perovskita, da densidade aparente e do tamanho de grão e para amostras contendo 100% PMN, esta dependência pode ser descrita qualitativamente pelo modelo de Looyenga. Com base neste modelo, a otimização das propriedades deilétricas do PMN deveriam ser obtidas para cerâmicas contendo 100% de fase perovskita, densidade aparente e do tamanho de grão da ordem de 5 a 8μm.
Title in English
Not available
Keywords in English
Not available
Abstract in English
In this work we have studied the synthesis of the ferroelectric relaxor Pb (Mg1Nb2/3)O3 (called PMN), its dielectric properties 9K(t, ν) and tanδ (T, ν) and their dependences with the apparent density and grain size. PMN powders have been prepared by classical method (milling and calcination of precursors) and by coprecipitation method in aqueous solution. The reactivity of the magnesium, which strongly influences the formation of the magnesium, which strongly influences the formation of a deleterious pyrochlore phase (Pb3Nb4O13), has been studied using oxide, carbonates and nitrates; the reactivity of lead has been determined for the two allotropic forms: PbO red and yellow. Concentration of PMN phase higher than 96% has been best obtained with the use of magnesium nitrate, orthorrombic lead oxide and niobium oxide, the mean particle size of the last two compounds being ,5μm and 1μm respectively. The PMN ceramics have been sintered at 950°C during 4h. However, addition of 4 wt% PbO and 2 wt% MgO were found fundamental to obtain a 100% PMn ceramics with apparent density þ > 0,9 þ th. The original synthesis pf PMN by coprecipitation I aqueous solution allowed the preparation of a 100% PMN powder; the occurrence of the parasitic pyrochlore phase was never observed during the various steps of the process. The dielectric properties (K and tanδ) have been studied as a function of the frequency an temperature. Dielectric constant Kmax = 17200 and 15400 at the Curie temperature (T ± 10°C) have been measured for sintered ceramics obtained with powders prepared classically and by coprecipitation respectively. The dependence of the dielectric constant on the percentage of the perovskite phase (PMN), the apparent density ρ and the grain size d, for ceramics containing 100% PMN, was shown to follow qualitatively, the Looyengas model. Consistent with this model, it was found that the optimum dielectric properties were attained for ceramics having 100% PMN perovskite phase, apparent density close to the theoretical density, and grain size between 5 to 8μm
 
WARNING - Viewing this document is conditioned on your acceptance of the following terms of use:
This document is only for private use for research and teaching activities. Reproduction for commercial use is forbidden. This rights cover the whole data about this document as well as its contents. Any uses or copies of this document in whole or in part must include the author's name.
Publishing Date
2015-04-07
 
WARNING: Learn what derived works are clicking here.
All rights of the thesis/dissertation are from the authors
Centro de Informática de São Carlos
Digital Library of Theses and Dissertations of USP. Copyright © 2001-2019. All rights reserved.