Growth and characterization of BSO and BTO photorefractive single crystals

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.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

Growth and characterization of BSO and BTO photorefractive single crystals

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.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

Jogos de tabuleiro e apropriação de ambientes: o círculo mágico e a suspensão tática do cotidiano

Jogos de tabuleiro são um verdadeiro portal para um mundo mágico. Os preparativos necessários para jogá-lo são quase ritualísticos, onde todos sentam em volta da mesa e estão envolvidos naquela atividade, seja para ser o melhor estrategista ou apenas para dar boas risadas. É inegável que os jogos de tabuleiro estão presentes na humanidade há séculos e que fizeram parte da infância de muitos brasileiros e brasileiras. No entanto, um fenômeno diferente surgiu há alguns anos e está tomando as prateleiras das casas e fazendo lojas especializadas e eventos de jogos de tabuleiro se multiplicarem. Estamos falando dos jogos de tabuleiro modernos. Este trabalho busca traçar um breve panorama sobre a formação deste cenário e tentar entender melhor como estes jogos são jogados em ambientes que a princípio não foram pensados para eles, como a praça de alimentação de um shopping, por exemplo. Entender o papel e que lugar os jogos de tabuleiro modernos ocupam na estrutura do cotidiano contemporâneo é mais uma das questões levantadas nesta dissertação.Board games are a true gateway to a magical world. The necessary preparations to play it are almost ritualistic, where everyone sits around the table and is engaged in that activity, whether to be the best strategist or just to have a good time. It is undeniable that board games have been present in humanity for centuries and were part of the childhood of many Brazilians. However, a different phenomenon has emerged a few years ago and is taking over the shelves of the houses and making specialty shops and board games events multiply. We are talking about modern board games. This work seeks to draw a brief overview of the formation of this scenario and try to better understand how these games are played in environments that were not originally intended for them, such as the food court of a mall, for example. Understanding the role and place of modern board games occupy in the structure of contemporary everyday life is one of the issues raised in this dissertation.105

Photoinduced Schottky Barrier in Photorefractive Materials

LGEP 2010 ID = 604International audienc

Photoinduced schottky barrier in photorefractive materials

Submitted by Franciele Moreira ([email protected]) on 2018-07-09T15:39:25Z No. of bitstreams: 2 Artigo - Jaime Frejlich - 2010.pdf: 653504 bytes, checksum: 5f410545191ea512cd4e1b1838db70e0 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5)Approved for entry into archive by Luciana Ferreira ([email protected]) on 2018-07-10T12:11:18Z (GMT) No. of bitstreams: 2 Artigo - Jaime Frejlich - 2010.pdf: 653504 bytes, checksum: 5f410545191ea512cd4e1b1838db70e0 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5)Made available in DSpace on 2018-07-10T12:11:18Z (GMT). No. of bitstreams: 2 Artigo - Jaime Frejlich - 2010.pdf: 653504 bytes, checksum: 5f410545191ea512cd4e1b1838db70e0 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2010-03We report on the first experimental evidence of a Schottky barrier effect produced by the action of light in an otherwise purely Ohmic contact between a nominally undoped photorefractive titanosillenite Bi12TiO20 crystal and a transparent conductive SnO2 electrode. The photorefractive crystal is sandwiched between two transparent electrodes and a Schottky barrier is built up in the illuminated crystal-electrode interface under the action of light with photonic energy large enough to excite charge carriers from the Fermi level into the conduction band. The contact remains purely Ohmic under illumination with photonic energy below that of the Fermi gap and the photoinduced barrier almost disappears if the photonic energy is large enough to produce electron-hole pairs

Electron Paramagnetic Resonance Study of Ternary CuII Compounds with Glycine and Phenanthroline

We report electron paramagnetic resonance (EPR) measurements at 9 and 34 GHz, and room temperature (T), in powder and single crystal samples of the ternary compounds of copper nitrate or copper chloride with glycine and 1,10-phenanthroline [Cu(Gly)(phen)(H2O)]∙NO3∙1.5H2O (1) and [Cu(Gly)(phen)Cl]2∙7H2O (2). In compound 1 the copper ions are arranged in 1-D chains along one of the crystal axes connected by syn-anti carboxylate ligands, while in 2 the array is nearly 3-D and the connections involve H-bonds and stacking interactions. The angular variation of the squared g-factor and the line width were measured as a function of orientation of the magnetic field (B0) in three orthogonal crystal planes. In both compounds we observed one resonance without hyperfine structure for any magnetic field orientation which we attribute to the collapse of the hyperfine coupling and of the resonances of two chemically identical but rotated coppers in the unit cell, produced by exchange interactions. We analyze the results in terms of the structures of the compounds and of the chemical paths connecting neighbor copper ions which support the exchange interactions between neighbor spins in the lattice. Considering the collapse of the EPR signals of rotated sites in the lattices we are able to set lower  limits to the exchange interactions, which are supported by weak equatorial-apical carboxylate bridges in 1, and by paths containing hydrogen bonds and aromatic interactions in 2. Broadening due to dipole dipole couplings and hyperfine interactions are strongly reduced by these exchange couplings and their role in the EPR line width is more difficult to recognize.Fil: Santana, Ricardo C.. Universidade Federal de Goias; BrasilFil: Araújo, Anderson B. C.. Universidade Federal de Goias; BrasilFil: Carvalho, Jesiel F.. Universidade Federal de Goias; BrasilFil: Calvo, Rafael. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Física del Litoral; Argentina. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Física; Argentin