Estudo numérico e experimental da matriz Sr2CoNbO6 adicionado com TiO2 para aplicações com ressoadores dielétricos de alta frequência

• Autor(a) principal: Morais, José Eduardo Vasconcelos de
• Data de Publicação: 2018
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Repositório Institucional da Universidade Federal do Ceará (UFC)
• Texto Completo: http://www.repositorio.ufc.br/handle/riufc/32662
• topic: Teleinformática; Microondas; Propriedades dielétricas; Dielectric properties; Radiofrequency; Thermal stability; Microwave

The search for new materials with useful electrical properties in areas of telecommunications engineering that use the microwave and radiofrequency region has intensified in recent years. Metal oxides belonging to the double perovskite family such as Sr2CoNbO6 (SCNO) and titanium oxide have interesting dielectric characteristics (low loss and high dielectric permissivity) and are widely applied in electro-electronic devices due to their dielectric characteristics. However, the dielectric properties variations of these two oxides on temperature effect show oposite variations. For the formation of the SCNO-TiO2 composite, the SCNO was synthesized via solid state reaction. Various concentrations of TiO2 in the composite formulation ranging from 0 to 80 wt% of TiO2 were used. The results of X-ray diffraction showed that the phases present after the sintering process were crystalline phases of SCNO, SrTiO3 and CoNbO4. The relative densities obtained by Picnometry and the densification obtained by scanning electron microscopy showed an increase up to the concentration of 20 wt% TiO2. The dielectric properties in the microwave range were investigated by the Hakki-Coleman technique, which showed an increase in dielectric permittivity (22-67) due to increased densification and formation of SrTiO3. For the dielectric loss a decrease was observed up to 20wt% of TiO2 influenced by the densification of the composite. The thermal stability of these composites showed that the TiO2 inserted greatly improved the thermal stability of the composites, since a signal inversion of τf was observed. The analysis of the dielectric and electrical properties of the composites by impedance spectroscopy in the frequency range analyzed at 1Hz-10MHz and at a temperature range of 30º-450ºC showed that the all samples showed that they have a heat transfer active transfer process and that through the Arrhenius relationship the studied composites showed a considerable increase of the activation energy with the increase of the added TiO2 concentration. The electrical responses obtained were adjusted using an R-CPE equivalent circuit model, showing the same profile in all samples. The dielectric resonators formed from the composites were tested as dielectric resonance antennas (DRA) and the performance of this material as antenna showed a reflection coefficient below -10dB, gain above 4.03dBi and efficiency above 60%.