Microstructure study and crystalline phase formation on Nb2O5-Ba9Ti2O20 microwave resonators

We report on the development of barium nanotitanate (Ba2Ti9O20) dielectric resonators (DRs) for microwave applications and their characterization regarding ceramic and high-frequency dielectric properties. Those DRs should meet the requirements of the dielectric constant as well as the quality factor high values and frequency high stability; for application as local oscillator of an INPE Communication Satellite. The ceramic were prepared using suitable powder mixtures composed of 0.818 BaCO3-0.182 TiO2 without and with addition of some contents of Nb2O5 (0.1, 0.2 and 0.4 mol), compacted by isostatic pressing with 300 MPa and sintering at 1360 degreesC in appropriate atmosphere. The initial powders and the sintered ceramics were characterized by X-rays diffraction and scanning electronic microscopy. The values of dielectric constant, resonance frequency, loaded quality factor due to the dielectric losses, and coefficient of frequency variation with the temperature was obtained using a special metallic box for these measurements. The comparative analyses of these results showed that the Nb2O5 content increases the amount of the formed phase Ba2Ti9O20 and the ceramic densification degree.