Tailoring morphological and electrical properties of nanoplate-ZnO varistors via sintering temperature†

In this study, ZnO nanoplates (crystallite size: 100 nm, thickness: 15 nm) were synthesized via a hydrothermal route. Varistors were then fabricated using these ZnO nanoplates incorporated with five oxide dopants (Bi₂O₃, Sb₂O₃, MnO₂, Co₃O₄, and Cr₂O₃) and sintered at 1000, 1100, and 1200 °C. A control varistor sample using micro-sized ZnO was also prepared. The effects of sintering temperature on the structural, mechanical, and electrical properties of ZnO-based varistors were systematically studied. Increasing the sintering temperature from 1000 °C to 1200 °C enlarged the grain size (1.7–6.8 μm), enhanced hardness (200–280 HV), and resulted in 17–19% shrinkage. At 1100 °C, the varistor achieved a balance of high nonlinearity (α = 48.5), low leakage current (J_L = 9.7 μA cm⁻²), and high breakdown threshold (E_b = 689 V mm⁻¹). Impedance analysis showed a resistive–capacitive transition at higher frequencies, while grain boundary resistivity at low frequencies (10^6.5–10⁸ Ω m) aligned with DC resistivity at the low applied electric fields. These results highlight the advantages of ZnO nanoplates in enhancing the electrical performance of varistors, making them promising for high-voltage applications.