Análise da estabilidade térmica e das propriedades elétricas da matriz Ba²TiSi²O8, com adição de TiO², para aplicações em alta frequência (Banda C)

Abstract

This work studied the dielectric properties in the radio frequency and microwave region of the Ba2TiSi2O8 ceramic (BTS) with additions of TiO2 and its possible applications as capacitive components or dielectric resonator antenna. X-ray diffraction was used for the structural characterization of the materials and Rietveld refinement to confirm the phases. The morphological analysis of the materials was carried out using scanning electron microscopy (SEM). Using Complex Impedance Spectroscopy (EIC), the relationships between the electrical properties and the microstructure of the matrix and composites were studied. The applied model that best describes the behavior found in the samples is the Havriliak-Negami model. From the EIC it was observed that the relative dielectric permittivity presented high values in BTS10 (ε’r = 2,6∙104) and BTS20 (ε’r = 2,5∙104), which allows them to be classified as materials with colossal permittivity. This is an important result due to the potential for applications in new storage systems, capacitive devices and microelectronics. Nyquist diagrams were used to evaluate the contribution of grain and grain boundary to the electrical response of the samples and adjusted using an equivalent circuit with two R-CPE associations. All samples presented grains (380 º - 460 ºC) with a conductive character. Grain boundaries are resistive for all composites in the temperature range studied. The temperature capacitance coefficient (TCC) values were also obtained for all samples, with an increase in the TCC value being observed for the compounds at all frequencies. Furthermore, EIC demonstrated that the activation energy of heat-activated processes decreases with addition, indicating a decrease in the resistive character of the materials. Regarding the analysis of dielectric properties in the microwave region, an increase in the dielectric permittivity (εr) and a decrease in the loss tangent (tg δ) of the samples were revealed, while the resonant frequency temperature coefficient (τf) showed a variation of - 47.0 ppm/°C to + 16.5 ppm/°C. In this analysis, the BTS30 sample stands out, which obtained τf = - 8.41 ppm/°C in the range required for technological applications. The numerical simulation presented good adjustments to the experimental data, with emphasis on gain and directivity, ranging from 4 dBi to 6 dBi and radiation efficiency above 80%. The results demonstrate that the samples can operate on C-band electronics, Wi-Fi devices, weather radar systems, etc.