Síntese e caracterização estrutural, dielétrica e magnética dos compósitos cerâmicos multifuncionais (1-x)K0,5Na0,5Nb0,7Ta0,3O3- xCoFe2O4 (0≤x≤0,3)

• Autor(a) principal: Carvalho, Fernando Marques
• Data de Publicação: 2016
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Repositório Institucional da UFG
• Texto Completo: http://repositorio.bc.ufg.br/tede/handle/tede/6821
• topic: KNNT; CFO; Magnetismo; Constante dielétrica; Compósito; KNNT; CFO; Magnetism; Dieletric constant; Composite; FISICA::FISICA DA MATERIA CONDENSADA

Lead-free multifunction composites are of great interest to the scientific community as they have several potential applications. Such composites were produced from the ferroelectric compound free of lead niobate and potassium sodium tantalate (KNNT) and the magnetic nanoparticles of cobalt ferrite (CFO). A particulate composite was then produced with the ferroelectric matrix and magnetic nanoparticles. First, the influence of the sintering temperature (950 and 1100 °C) on the ceramic densification process was investigated. Ceramics sintered at 950 °C showed very low density, unlike those sintered at 1100 °C, which have a density of 90%. The microstructure of the composites and how the magnetic particles are distributed in the matrix were investigated. The composites presented the perovskite, spinel and tungsten bronze structural phases; The lattice constant of all crystalline phases remained constant, so there was no migration of cations between the distinct phases. The value of the relative dielectric constant of the pure KNNT is 700, which is comparable to the values found in the literature. In the composites, the dielectric constant value decreases coherently with the amount of cobalt ferrite. The coercivity of the nanoparticles before and after the sintering is 1494 and 675 Oe, respectively, in the composites the value of coercivity remains constant. On the other hand, the saturation magnetization of nanoparticles before and after sintering is 63 and 68 emu/g, respectively. The value of the saturation magnetization reduces coherently with the amount of ferrite present in the other composites. In this way, it was shown that the electrical and magnetic properties coexist in the composite, since the magnetic properties depend exclusively on the cobalt ferrite.