Fases nanoscópicas de manganitas magnéticas
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Data
2013-03-22
Autores
Mazini, Melânia Cristina [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
A compreensão do comportamento estruturas, magnético e eletrônico para estes materiais ainda permanece um problema em aberto e tem exigido grandes esforços, principalmente, quando se refere aos diferentes estados de oxidação apresentados pelos elementos metálicos que as compõem. A flutuação de valência apresentada pelos ínos metálicos e a correspondente variação da estequiometria de oxgiênio nesses compostos são variáveis fundamentais para a correta interpretação de suas respostas físicas. Condições de preparo, como rota de síntese, tratamentos térmicos, razões de aquecimento e resfriamento, condições atmosféricas, são fatores a serem considerados nos estudos desses materiais, pois influenciam diretamente em suas composições estequiométricas. As manganitas aqui estudadas foram sintetizadas pela rota de síntese baseada no Método dos Precursores Poliméricos Modificados (MPPM), uma variação do Método Pechini (MP). Trata-se de um método químico para o preparo de amostras de óxidos metálicos e tem sido utilizado como uma excelente alternativa às tradicionais rotas físicas de síntese, como a rota de Reação em Estado Sólido (RES), pois permitem produzir amostras de excelente homogeneidade, bastante superiores às amostras convencionais preparadas via RES, maior controle no tamanho de partícula, por requerer temperaturas menoes para obtenção da fase cristalográfica do material, dentre outros fatores. Para a caracterização estrutural das amostras sintetizadas técnicas de Difração de Raios X (DRX) associada ao Método de Refinamento Rietveld (MRR) e Microscopia Eletrônica de Varredura (MEV) foram empregadas. Através da análise de DRX e refinamento Rietveld foi verificado a formação da fase cristalográfica dos materiais sintetizados, bem como foi possível identificar presença de fases secundárias para as manganitas...
In this work, NiMn2O4, CuMn2O4, CoMn2O4, Ni1-xCuMn2O4 and Ni1-xCoxMn2O4 (x=0,2; 0,4;0,6 e 0,8) oxide manganites with spinel structure were studied. The understangind of structural, magnetic and electrical response to these materials still remains an open question and requires large efforts, especially considering the valence fluctuation presented by metallic ions that compose these samples. The valence fluctuation presented by the metallic ions and the corresponding deficient oxygen stoichiometry are crucial factors to the correct description of the physical response in this material. Some factors, such as synthesis route, thermal history, heat and cooling rates, atmospheric gas flux, must be considered since they are directly responsible for the stoichiometric composition exhibited by these materials. In this study, manganite samples were synthesized by the Modified Polymeric Precursor Method (MPPM), a Pechini Method (PM) variation. MPPM is a chemical method to prepare metallic oxides samples and has been used as an excellent alternative to physical traditional synthesis routes, such as Solid State Reaction (SSR). MPPM allows to produce excellent homogeneous samples, with higher quality if compared to traditional ceramic routes, since this method is able to control the particle size considering heat-treatment lower tempeartures to obtain the crystallographic phase, among other advantages. The structural characterization was done by X Ray Diffraction (XRD) associated to Rietveld Refinament Method and Scanning Electron Micrograph (SEM). By the XRD and Rietveld refinament was observed the crystallographic phase was obtained, was also observed that the CoM2O4 and Ni-xCuxMn2O4 (with x > 0,6) manganites presented secondary phases. Magnetic behavior studies were also developed to these materials by DC magnetic measures... (Complete abstract click electronic access below)
In this work, NiMn2O4, CuMn2O4, CoMn2O4, Ni1-xCuMn2O4 and Ni1-xCoxMn2O4 (x=0,2; 0,4;0,6 e 0,8) oxide manganites with spinel structure were studied. The understangind of structural, magnetic and electrical response to these materials still remains an open question and requires large efforts, especially considering the valence fluctuation presented by metallic ions that compose these samples. The valence fluctuation presented by the metallic ions and the corresponding deficient oxygen stoichiometry are crucial factors to the correct description of the physical response in this material. Some factors, such as synthesis route, thermal history, heat and cooling rates, atmospheric gas flux, must be considered since they are directly responsible for the stoichiometric composition exhibited by these materials. In this study, manganite samples were synthesized by the Modified Polymeric Precursor Method (MPPM), a Pechini Method (PM) variation. MPPM is a chemical method to prepare metallic oxides samples and has been used as an excellent alternative to physical traditional synthesis routes, such as Solid State Reaction (SSR). MPPM allows to produce excellent homogeneous samples, with higher quality if compared to traditional ceramic routes, since this method is able to control the particle size considering heat-treatment lower tempeartures to obtain the crystallographic phase, among other advantages. The structural characterization was done by X Ray Diffraction (XRD) associated to Rietveld Refinament Method and Scanning Electron Micrograph (SEM). By the XRD and Rietveld refinament was observed the crystallographic phase was obtained, was also observed that the CoM2O4 and Ni-xCuxMn2O4 (with x > 0,6) manganites presented secondary phases. Magnetic behavior studies were also developed to these materials by DC magnetic measures... (Complete abstract click electronic access below)
Descrição
Palavras-chave
Quimica - Sintese, Compostos metalicos, Oxidação, Polimeros, Oxidos metalicos, Chemistry - Synthesis
Como citar
MAZINI, Melânia Cristina. Fases nanoscópicas de manganitas magnéticas. 2013. 124 f. Dissertação (Mestrado) - Universidade Estadual Paulista Júlio de Mesquita Filho, Faculdade de Ciências de Bauru, 2013.