High thermal stability of RF dielectric properties of BiVO_4 matrix with added ZnO

摘要

In this work, a complex impedance spectroscopy study of bismuth vanadate (BiVO_4) ceramics with different additions of ZnO (25, 50, and 75 wt %) was performed. BiVO_4 (BVO) was synthesized by the reaction method in solid-state and calcined at 500 °C and BVO-ZnO composites were moulded in sintered ceramic pellets at 700 °C. X-ray diffraction (XRD) was used to analyse the crystal structure of BVO and the BVO-ZnO composites; none spurious phase was observed during the synthesis. Analysis by complex impedance spectroscopy (CIS) showed that increasing the concentration of ZnO reveals increased activation energy due to thermo-activated charge transfer for the sample with 25 wt % ZnO. At room temperature, the increase in the ZnO concentration in the BVO matrix maintained a high value for the dielectric constant (ε), in the order of 10~4 at a frequency of 1 Hz. Average normalized change (ANC) was used to identify the temperature at which the available density of trapped charge states vanishes in each sample. The temperature coefficient of capacitance was positive for BVO and negative for composites. The adjustment through the equivalent circuit presented excellent electrical response for the composites, and identified an association with three resistors, each in parallel a constant phase element, showing the influence of grain and grain boundary on the process of thermo-active conduction.