Preparação pelo método poliol modificado, caracterização estrutural e espectroscópia de nanopós de niobato de potássio e neodímio e de suas condições sólidas dopadas em európio

• Ano de defesa: 2015
• Autor(a) principal: Namikuchi, Eliane Ayumi [UNESP]
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Estadual Paulista (Unesp)
• Palavras-chave em Português: Físico-química; Niobatos - Estrutura; Cerâmica - Propriedades elétricas; Dialétricos; Análise spectral
• Link de acesso: http://hdl.handle.net/11449/127830

This work is based on preparation and structural and spectroscopic characterization of potassium neodymium niobate oxide semiconductors nanopowders and their Eu-doped solid solutions K2Nd(1-x)EuxNb5O15, where x = 0; 0.0025; 0.025; 0.05 and 0.1, prepared by chemical synthesis, using the Modified Polyol method. Precursor powders of K2NdNb5O15 and their Eu-doped solid solutions were investigated by Thermogravimetry (TG) and Differential Scanning Calorimetry (DSC), proposing a chemical formula for each precursor. The structural characterization was carried out by X-ray diffraction. The structural parameters were determined by Rietveld method using the FullProf program. Structural-parameter refinements by the Rietveld method were performed by taking into account the noncentrosymmetric space group P4bm. The best theoretical adjustment for the K2NdNb5O15 was obtained assuming that each pentagonal site (4c (x, x + 1/2, z)) is occupied by K + cátions, the tetragonal sites (2a (0,0, z)) are occupied by Nd3+ and octahedral sites by Nb5+ cations. For solid solutions, pentagonal sites are occupied by cations K+ and Eu3+. From crystallographic parameters systems unit cells were built, and derived the atomic displacement (Δz) of niobium atom in the z-plane, from the central position of the [NbO6] octahedron. The addition of europium in the K2NdNb5O15 host structure led to changes in lattice parameters and the decrease in the unit cell volume, consistent with the distortion degree of [NbO6] octahedra. The average crystallite size of the investigated systems varied from 18.25 to 26 nm. The chemical bonds of K2NdNb5O15 and their solid solutions were analyzed by Infrared spectroscopy (FTIR) and Nb-O bond characteristic bands were observed. Electronic transitions of neodymium were analyzed by diffuse reflectance spectroscopy in the UV-Vis region. The band gap values were also determined and they are close to the values of semiconductors found in the...