Effect of multi-donor doping on structure and electrical properties of DC ZnO varistor ceramics

Abstract

Direct-current ZnO varistor ceramic samples were prepared by traditional ceramic sintering process with B2O3, In2O3 and Al2O3multi-donor doping. The effects of B2O3 doping ratio (0.1%-0.4%, molar fraction) on the microstructure and electrical properties of direct-current ZnO varistor ceramics were investigated. The phase, morphology, composition and electrical properties of the samples were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and digital source meter. The results show that the co-doping of multi-donor dopants (Al2O3, In2O3 and B2O3) can significantly improve the comprehensive properties of direct-current ZnO varistor ceramics. Al3+ improves the conductivity of the samples and reduces the residual voltage ratio of the samples; In3+ restricts the growth of grains through pinning effect and improves the voltage gradient of the samples; the doping of B3+ improves the surface state density of the sample, increases the barrier height and effectively suppresses the increase in leakage current. When the doping amount of B2O3 is 0.3%, the comprehensive performance of the sample is the best: the voltage gradient is 486 V/mm, the leakage current density is 0.58 μA/cm2, the nonlinear coefficient is 85, and the residual voltage ratio is 1.55.

Keywords

• surface state density
• grain
• conductivity
• residual voltage ratio