Fabrication of high voltage gradient ZnO nanoparticle-Bi 2 O 3 -Mn 2 O 3 -based thick film varistors at various sintering temperature

In this research, 20 nm zinc oxide nanoparticles were utilized to fabricate significant voltage gradient zinc oxide nanoparticle-Bi 2 O 3 -Mn 2 O 3 -based thick film varistors (TFVs) by applying screen printing method. Different low temperatures during the sintering process had a considerable effect on the zinc oxide nanoparticle-based TFVs. In particular, the low temperatures improved the growth of ZnO grains, which was obvious even at 550 °C. The huge surface area of the 20 nm zinc oxide encouraged an intense surface interaction even at minimal sintering temperatures. The sintering technique also enhanced the internal structure of the crystal. Minimizing the fundamental compressive stress depended on the XRD lattice constant and the FWHM analysis. The variable temperatures of the sintering process considerably impacted the electrical behaviours of the samples. A remarkable increase in the voltage gradient of the varistor sintered up to 5732.5 V/mm at 700 °C was observed. The electrical resistivity dropped dramatically from 621.8 kΩ.cm (varistor at 550 °C) to 147.3 kΩ.cm at 800 °C sintering temperature. The small size of grains with perfect boundaries was the main reason for the enhancement of the voltage gradient. The optimal electrical characteristics with a 63 nonlinearity coefficient and 103 μA leakage current were achieved in the varistor sintered at 700 °C. Moreover, maximum permittivity and minimum dissipation factor were attained through the minimal frequency range. Therefore, the sintering process could be applied as a novel technical approach for the dominant voltage gradient of zinc oxide nanoparticle-based TFVs with enhanced microstructural and electrical behavior and good nonlinearity.