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Seminários do CCMC - Growth of single crystal fibers of strontium titanate: a study of persistent photoconductivity for optical applications

Persistent photoconductivity was observed in strontium titanate single crystals when vacancies are produced in it. At paper recent, it present an annealed method for create titanium vacancies, that increases free-electron concentration significantly after illuminating of the sample. Then with turn-off light a high conductivity persistent was observed at room temperature. The persistent photoconductivity is attributed to the excitation of an electron from a vacancy into the conduction band, with a low recapture rate. The SrTiO3 is an oxide semiconductor that has interest for it is fundamental properties and new application fields, for example, at the development of active optical memories. In this way, the "Laser-Heated Pedestal Growth (LHPG)” method allow growth to single-crystalline fibers of millimeter and sub-millimeter dimensions. The LHPG technique compared with the conventional crystal growth methods has significant advantages, such as high pull rate (mm/min),  not used crucible, allow crystals growth with high melting point ( ³1500°C) and melting zone has its reduced size (<1mm3).  In previous work, it reports on the influence of the ceramic feed rod treatment on SrTiO3 fiber quality and optimization of ceramic pedestal processing that allows improvements to be made on the final quality in a simple manner. The other hand, the oxygen vacancies produce a wide range of colors, from yellow or light brown to blue-violet or black. Very small amounts of oxygen vacancies can produce these color changes. Pure SrTiO3 is colorless, transparent in the visible region, and is an insulator when it contains stoichiometric amounts of oxygen (band gap = 3.2 eV). We observed that the LHPG technique might be an alternative method to create vacancies in the fiber to generate persistent photoconductivity, where the vacancies depending of the pulling rate. In this work, we present growth result of the single-crystal strontium titanate fiber. 

Minicurso sobre História da Ciência, Meio ambiente e Energia é finalizado a alunos de Ensino Médio da E.E. Sebastião de Oliveira Rocha

Na última semana, foi finalizado na E.E. Professor Sebastião de Oliveira Rocha, da cidade de São Carlos-SP, o minicurso “História da Ciência e Meio Ambiente: as demandas por Energia através da História”, ministrado pela pesquisadora do Laboratório de Difusão Científica (LaDiC) do CCMC, Amanda Murgo. O minicurso é resultado de uma pesquisa desenvolvida por Murgo sob orientação do Prof. Antonio Carlos Hernandes.


Synthesis, characterization, structural refinement and optical absorption behavior of PbWO4 powders

The present paper describes the synthesis, characterization, structural refinement and optical absorption behavior of lead tungstate (PbWO4) powders obtained by the complex polymerization method heat treated at different temperatures for 2 h in air atmosphere. PbWO4 powders were characterized by X-ray diffraction (XRD), Rietveld refinement, Fourier transform Raman (FT-Raman) spectroscopy and ultraviolet–visible (UV–vis) absorption spectroscopy measurements. XRD, Rietveld refinement and FT-Raman revealed that PbWO4 powders are free of secondary phases and crystallizes in a tetragonal structure. The UV–vis absorption spectroscopy measurements suggest the presence of intermediary energy levels into the band gap of structurally disordered powders.

Laécio Santos Cavalcante, Júlio César Sczancoski, Viviane Cristina Albarici, J.M.E. Matos, José Arana Varela, Elson Longo

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XXXVIII Congresso del Chimici Teorici di Esspresione Latine (Quitel 2012)


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Pesquisadores do CCMC apresentam trabalhos na 4ª SIFSC e 22º SIICUSP


Doutorado desenvolvido no CCMC recebe prêmio CAPES de melhor tese – edição de 2014


Seminários do CCMC - História da Ciência e Meio Ambiente: as demandas por Energia no Mundo Contemporâneo



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