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Master's Dissertation
DOI
10.11606/D.76.1994.tde-14012009-093345
Document
Author
Full name
Jesiel Freitas Carvalho
Institute/School/College
Knowledge Area
Date of Defense
Published
São Carlos, 1994
Supervisor
Committee
Andreeta, José Pedro (President)
Carvalho, Rene Ayres
Sochaczewsky, Jaime Frelich
Title in Portuguese
Crescimento e caracterização de monocristais fotorreativos: BSO e BTO
Keywords in Portuguese
BSO
BTO
Método de Rietveld
Monocristais
Abstract in Portuguese
Neste trabalho crescemos monocristais de Bi12SiO20 (BSO) e de Bi12TiO20 (BTO). Os cristais de BSO foram crescidos pela técnica de Czochralski a partir da fase líquida com composição molar 6Bi2O3:1SiO2. Os melhores resultados foram obtidos para taxas de puxamento entre 1 e 2,5mm/h, a velocidade de rotação foi mantida constante em 20rpm. Os cristais de BTO foram crescidos pelo método top-seeded solution Growth (TSSG) a partir da composição molar 10Bi2O3:1SiO2, com taxas de puxamento menores que 0,3mm/h e velocidade de rotação entre 16 e 30 rpm. A qualidade dos cristais foi avaliada utilizando microscopia óptica e eletrônica, corrosão seletiva e raios-x. Por microscopia óptica identificamos os defeitos macroscópicos e discutimos sua natureza e possíveis causas. Utilizando a técnica de ataque químico seletivo, analisamos a morfologia das figuras de ataque e estimamos a densidade de deslocações. Visando identificar defeitos de estequiometria, fizemos medidas de composição por microanálise eletrônica. Para a caracterização cristalográfica, calculamos o parâmetro de rede por difração de raios-x usando o método do pó e confirmamos a estrutura cristalográfica através do método de Rietveld. E, ainda, medimos a atividade óptica que é uma constante característica dos cristais.
Title in English
Growth and characterization of BSO and BTO photorefractive single crystals
Keywords in English
BSO
BTO
Rietveld method
Single crystals
Abstract in English
In this work we grew Bi12SiO20 (BSO) and Bi12TiO20 single crystals. The BSO crystals have been grown from the melt composition of 6Bi2O3:1SiO2 by the Czochralski method. The best results were obtained at pulling rates from 1 to 2.5m/h, the rotation rate of 20rpm was constant. The BTO crystals have been grown by the top-seeded solution growth technique from a 10Bi2O3:1SiO2 solution with pulling rates less than 0.3mm/h and rotation rates from 16 to 30rpm. The crystal quality was examined by optical and scanning electron microscopy, selective etching, and x-ray diffraction. We identified the macroscopic defects by optical microscopy and discussed their nature and probable origin. Using selective etching, we analyzed the etching pits morphology and evaluated the dislocation density. To identify stoichiometric defects, composition measurements by electron probe microanalysis were made. To obtain crystallographic characterization, we calculated the cell parameter by powder method x-ray diffraction and used the Rietveld method to verify the crystallographic structure. And, also, we measured the optical activity, a constant of the crystals.
 
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Publishing Date
2009-01-19
 
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