Effect of capacitance on ZnO-Bi₂O₃-Yb₂O₃ based varistor for nanosecond transients

Abstract

The microstructure and electrical properties of ZnO-ZnO-Bi₂O₃-Yb₂O₃ based varistor ceramics were investigated with various temperature effects from 900 °C to 1050 °C. From the results, it was observed that the increase of sintering temperature offers a reduced capacitive effect from 0.460 nF to 0.321 nF. Furthermore, the grain sizes of varistors were varied from 6.8 μm to 9.8 μm. The consequence of such smaller grain sizes provided a better voltage gradient of about 895 V/mm for the disc sintered at 900 °C and fallen drastically to 410 V/mm for the sample sintered at 1050 °C. In addition, there was an increase of non-linearity index to a maximum value of 36.0 and reduced leakage current of 0.026 mA/cm². However, the density of the varistor decreased with an increase of temperature from 5.41 g/cm³ to 5.24 g/cm³. With this base, the influence of varistor capacitance and high voltage gradient were scrutinized and it led an improved transition speed of the varistor assembly from non-conduction to conduction mode during intruding nanosecond transients.

Keywords

capacitance / metal oxide varistor / nanosecond transient / rare earth oxide / transition delay / ytterbium oxide

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