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Made available in DSpace on 2014-10-09T12:52:09Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:58:11Z (GMT). No. of bitstreams: 0 / Vidros fosfatos são investigados desde a década de 50, sendo obtidos a partir da fusão de compostos inorgânicos em temperaturas relativamente baixas (1000- 1200oC), apresentando baixas temperaturas de transição vítrea. No entanto, estes vidros são sensíveis a ambientes com altas umidades relativas, mostrando certa fragilidade em relação à durabilidade química. Vidros fosfatos de ferro foram obtidos previamente a partir da fusão de precursores inorgânicos apropriados, tanto em fornos de indução, como em fornos elétricos convencionais. A presença de ferro promove o aumento da durabilidade química, suficiente para possibilitar o uso destes materiais como meio imobilizador de rejeitos radioativos ou como fibras de resistência mecânica, adequadas para aplicações específicas. O uso de microondas tem sido investigado exaustivamente, pois possibilita um aquecimento rápido e homogêneo dos materiais. A radiação de microondas interage diretamente com dipolos e íons presentes na estrutura do material promovendo o seu aquecimento. Vidros fosfatos contendo nióbio também já foram produzidos por meio do aquecimento de precursores em fornos de microondas. Outros vidros contendo ferro em sua estrutura foram produzidos por fornos convencionais e tiveram suas estruturas analisadas. Mas mesmo assim, ainda não foi reportada síntese de vidros fosfatos com ferro a partir da fusão de precursores em fornos de microondas. Neste trabalho, misturas de fosfato de amônia dibásico (NH4)2HPO4 e magnetita (Fe3O4) ou (NH4)2HPO4 e ferrita (Fe2O3) foram expostas às microondas, com radiação eletromagnética de 2,45 GHz. Propõe-se que a absorção desta radiação pelo material à temperatura ambiente cause o aquecimento até a completa fusão e homogeneização do material. Os vidros fosfatos de ferro obtidos foram caracterizados por espectroscopia Mössbauer, Difratometria de raios X e Análise térmica diferencial. Uma comparação é realizada com vidros obtidos por meio da fusão em fornos elétricos. / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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Open-framework inorganic materials constitute an important area of study in materials chemistry, because of their potential applications in areas such as sorption and catalysis. After the discovery of nanoporous aluminium phosphates by Flanigen et al in 1982, there has been a tremendous growth in the area of porous solids. Most of them are based upon oxygen containing materials especially phosphates, and they exhibit fascinating architectures with unusual bonding and coordination environment. Besides metal phosphates and phosphites, inorganic-organic hybrids constitute an important family of open-framework structures. In this thesis, results of investigations of a variety of open-framework metal phosphates, metal phosphites, as well as a new family of phosphite-oxalates are presented. More importantly, studies directed towards the synthesis and understanding of the magnetic properties of various transition metal phosphates, phosphites, phosphite-oxalates and the upconversion behavior of uranium phosphites are discussed at length. In Chapter 1 of the thesis an overview of inorganic open-framework materials is presented. In Chapter 2 and 3, the synthesis, structure of open-framework zinc (Part A of both Chapters) and synthesis, structure and magnetic properties of open-framework iron (Part B of both Chapters) are presented. Some of these compounds show unusual structure and interesting properties. For example, two-dimensional iron phosphate exhibits ferrimagnetism whereas three-dimensional iron phosphate with SBU-6 and SBU-2 is antiferromagnetic. The three-dimensional iron phosphite exhibits small polarization at low field. In Chapter 4, we present a new family of organically templated hybrid materials synthesized by partially substituting the phosphite by the oxalate ion in manganese, iron and cobalt phosphites. These exhibit a wide range of structures in which the oxalates play an unusual dual role. Some of these compounds show interesting magnetic properties. For example, manganese phosphite-oxalate shows magnetic polarizations on application of high field at low temperatures and iron phosphite-oxalate exhibit ferromagnetism at very low temperature. While a large number of organically templated transition and main-group element phosphites have been synthesized, research on lanthanide and actinide phosphites has been rare. Most of the reported open-framework phosphate and phosphite compounds of uranium possess uranium in +6 oxidation state. The possibility of building open architectures of uranium phosphites has been explored in Chapter 5. The results have been rewarding and both layered and three-dimensional structures have been prepared. Two of them contain uranium in +4 state and exhibit upconversion behavior.

Depuis la mise en évidence des potentialités du phosphate LiFePO4 comme électrode positive de batteries lithium-ion, un très fort regain d’intérêt pour les phosphates de fer est actuellement observé. Dans cette optique de recherche de nouveaux matériaux, notre intérêt s’est porté sur la phase Na3Fe3(PO4)4 et sur des monophosphates de fer et de manganèse de type alluaudite LiXNa1-XMnFe2(PO4)3. Leurs structures, respectivement en couche et en chaines, en font de bons candidats pour des applications en tant que matériau d’électrode pour des batteries au lithium ou au sodium. Notre étude porte donc, d’une part, sur la synthèse et la caractérisation structurale de ces phases, et d’autre part sur leurs propriétés physiques et électrochimiques. / Since the discovery of highly interesting properties for LiFePO4 as a positive electrode material in lithium ion batteries, the search for novel polyanion-based insertion hosts is intense. Actually, cathodic materials based on iron phosphates exhibit high stability and economical and environmental interests. In this context, we were interested in Na3Fe3(PO4)4 with a lamellar structure and in alluaudite-like iron and manganese phosphates LiXNa1-XMnFe2(PO4)3 which structure exhibits tunnels. This work deals, in one hand, on the synthesis and the structural characterisation of these materials and in the other hand on their physical and electrochemical properties as positive electrode for lithium and sodium batteries.