Vidros e vitrocerâmicas em sistemas oxifluoretos
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Data
2003
Autores
Bueno, Luciano Avallone [UNESP]
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
Este trabalho foi dividido em 5 etapas. Primeiramente, realizou-se um estudo estrutural de vidros e vitrocerâmicas no sistema PbGeO3-PbF2-CdF2 utilizando-se das técnicas de Ressonância Magnética Nuclear (RMN-19F) e condutividade iônica, juntamente com os resultados de absorção de raios-X e espectroscopia vibracional obtidos no trabalho de mestrado. Foi proposta uma estrutura para estes materiais em que “clusters” de íons fluoretos se encontram dispersos dentro da matriz vítrea do metagermanato. Numa segunda parte estudou-se a evolução da condutividade iônica destes materiais em função da composição dos vidros e vitrocerâmicas. Dependendo da concentração de PbF2 pode-se obter materiais com valores de condutividade próximos e superiores àqueles encontrados para o condutor superiônico PbF2, indicando uma possível aplicação destes materiais em baterias no estado sólido. Amostras vítreas foram então dopadas com diferentes concentrações de íons Tm3+ e codopadas com Tm3+/Ho3+ com o objetivo de se estudar as propriedades de emissão em 1,47 μm, relacionadas à transição radiativa 3H4→3F4 do Tm3+. Com o aumento da concentração de Tm3+ ocorre uma diminuição na eficiência da emissão em 1,47 μm devido a supressão por concentração. Este efeito é minimizado quando se adiciona íons Ho3+, que são utilizados para que ocorra transferência de energia entre estes íons e aumente a eficiência em 1,47 μm. Notou-se também, que há uma concentração ótima de Ho3+ para este processo ocorrer. Com o objetivo de se obter vitrocerâmicas transparentes dopadas com íons lantanídeos, foi estudado a influência destes no processo de nucleação da fase cúbica do PbF2 na matriz vítrea, com relação ao tamanho dos íons e a variação da concentração. Observou-se que com o aumento da concentração e também com o aumento dos íons introduzido...
In the present study the structure of glasses and glass-ceramics in the PbGeO3- PbF2-CdF2 system was studied using 19F-NMR and ionic conductivity techniques together with the EXAFS and Raman spectroscopy. Raman and EXAFS data lead to the suggestion of an heterogeneous structure at the molecular scale. A metagermanate chain similar to the one found in the monoclinic PbGeO3 is suggest to be the basic structural feature for the lead cadmium fluorogermanate glasses studied here. 19F NMR data analysis lead to F-F distances similar to the ones found in pure crystalline phases suggesting that fluorine rich regions should be present permeating the metagermanate chain. Dynamic parameter also obtained from NMR data indicate that these glasses are fairly good ionic conductors. The structural model proposed could well account for the high values of ionic conductivity found here and also by several researchers in related systems. High mobile fluorine atoms would find a diffusion path through the fluorine rich areas proposed to exist based in the spectroscopic study performed here. These areas also would display higher thermodynamic probabilities for the formation of nuclei which will evolve to the nanocrystalline domains found in transparent glass ceramics that can be prepared from these oxifluoride glasses. Emission at 1,47 μm due the radiative electronic transition of Tm3+ ions was investigated in Tm3+ and Tm3+-Ho3+ doped glasses. Increasing the Tm3+ contents a concentration quenching was observed. This effect is minimized when Ho3+ is added due to an energy transfer process. The nucleation effect in oxifluoride glasses was observed when lanthanide ions were added. The process of nucleation of cubic PbF2 was observed with the increase of the concentration and the size of ions. This characteristic was also evaluated through the values of the Tx-Tg thermal parameter. Transparent glass ceramics...(Complete abstract click electronic access below)
In the present study the structure of glasses and glass-ceramics in the PbGeO3- PbF2-CdF2 system was studied using 19F-NMR and ionic conductivity techniques together with the EXAFS and Raman spectroscopy. Raman and EXAFS data lead to the suggestion of an heterogeneous structure at the molecular scale. A metagermanate chain similar to the one found in the monoclinic PbGeO3 is suggest to be the basic structural feature for the lead cadmium fluorogermanate glasses studied here. 19F NMR data analysis lead to F-F distances similar to the ones found in pure crystalline phases suggesting that fluorine rich regions should be present permeating the metagermanate chain. Dynamic parameter also obtained from NMR data indicate that these glasses are fairly good ionic conductors. The structural model proposed could well account for the high values of ionic conductivity found here and also by several researchers in related systems. High mobile fluorine atoms would find a diffusion path through the fluorine rich areas proposed to exist based in the spectroscopic study performed here. These areas also would display higher thermodynamic probabilities for the formation of nuclei which will evolve to the nanocrystalline domains found in transparent glass ceramics that can be prepared from these oxifluoride glasses. Emission at 1,47 μm due the radiative electronic transition of Tm3+ ions was investigated in Tm3+ and Tm3+-Ho3+ doped glasses. Increasing the Tm3+ contents a concentration quenching was observed. This effect is minimized when Ho3+ is added due to an energy transfer process. The nucleation effect in oxifluoride glasses was observed when lanthanide ions were added. The process of nucleation of cubic PbF2 was observed with the increase of the concentration and the size of ions. This characteristic was also evaluated through the values of the Tx-Tg thermal parameter. Transparent glass ceramics...(Complete abstract click electronic access below)
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Compostos inorganicos, Vidro, Química inorgânica, Inorganic chemistry
Como citar
BUENO, Luciano Avallone. Vidros e vitrocerâmicas em sistemas oxifluoretos. 2003. 178 f. Tese (doutorado) - Universidade Estadual Paulista, Instituto de Química, 2003.