Dielectrical and structural studies of composite matrix BiVO4–CaTiO3 and temperature effects by impedance spectroscopy
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In this work, we have analysed the effects of adding CaTiO3 (CTO) and changing the temperature on the dielectric and electric properties of ceramic matrix BiVO4 (BVO) in the radiofrequency range. BVO was synthesized by a calcination process at 500 °C and ceramic composites were prepared by the addition of CTO (8, 16, 24, 28 and 32 wt%). These composites were moulded in ceramic pellets and sintered at 800 °C. The crystal structures of BVO and composites were analysed by X-ray diffraction and no spurious phase was detected in the synthesized BVO. Complex impedance spectroscopy observed the presence of a thermo-activated charge transfer process with activation energy increasing with CTO concentration in the samples. The dielectric constant (ε) measured in radio frequency for ceramic composites presented high values that ranged from 26 to 9 k for BVO to BV32, respectively, at room temperature and a frequency of 1 Hz. The electrical response obtained by composites were fitted through an equivalent circuit composed of three associations in parallel with the resistance of a constant phase element, which showed minor deviations between the fitted and experimental data. The temperature coefficient of capacitance displayed negative and positive values in CTO-based composites and pure BVO, respectively; these characteristics are favourable for the application of composites in the radio frequency band.
The authors are grateful to CNPq (402045/2013-0), the US Air Force Office of Scientific Research (AFOSR) (FA9550-16-1-0127) and CNPq (Process: 402561/2007-4, Edital MCT/CNPq nº 10/2007) for providing financial support.
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