Abstract
In this study, the impact of CaO doping on the microstructure, phase and electrical properties of the ZnO–Bi2O3 system was studied. The powder was synthesized by the solution combustion route. Reduction in the crystallite size of ZnO from 23 nm to 17 nm of the powder sample with CaO doping was noted. Conventional sintering was used to consolidate the powders. Solid state reacted compositions revealed, from X-ray diffraction, formation of two phases (a) Ca4Bi6O13 at 750 °C and (b) Ca0.89Bi3.11O5.56 at 900 °C. An increase in density from 4.21 to 5.45 gcc−1 and a decrease in grain size from 4.50 to 1.54 μm with increasing CaO doping were also observed. A grain growth mechanism in the ZnO–Bi2O3–CaO system was proposed. The breakdown field increased up to 1 wt % CaO (27 kV cm−1) and after that decreased. Impedance spectroscopic investigation, in the temperature range of 100300 °C and frequency range of 0.1 Hz -1M Hz, exhibited two relaxations. These were attributed to defects formed. The two-stage activation energy of conductivity was noticed, which was similar to that observed in complex ZnO varistor systems.
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