The Impact of Sintering Temperature on the Microstructure and Electrical Characteristics of Varistor Ceramics Containing V2O5-doped ZnO-Bi2O3-Sb2O3 and MnO2 Additives

Abstract

This study explores the enhancement of ZnO varistor ceramics as voltage surge protectors for electronic components by incorporating various metal oxides, including Bi₂O₃, as varistor-forming agents. The investigation focuses on the impact of V₂O₅ doping in ZnO-Bi₂O₃-Sb₂O₃-MnO₂ varistor ceramics to achieve maximum nonlinearity and low leakage current. A mixture of powdered materials (98.1 mol% ZnO, 0.7 mol% Bi₂O₃, 0.3 mol% Sb₂O₃, 0.7 mol% MnO₂, and x mol% V₂O₅) underwent a 24-hour ball milling process, drying, and grounding. The resulting powder was uniaxially pressed into 10 mm diameter, 1 cm thick disks, then sintered at 1240 °C for 4 hours, with a heating and cooling rate of 5°C/min for all compositions. Electrical and microstructural properties were examined for varying V₂O₅ doping levels (x = 0.0 to 0.6 mol%) in ZnO-Bi₂O₃-Sb₂O₃ and MnO₂ varistor ceramics. The maximum barrier height observed was 0.68 eV, corresponding to the highest nonlinearity coefficient 11.25. Minimal leakage current, approximately 1×10^-4 mA/cm², was observed for doping levels of 0, 0.08, 0.20, 0.40, and 0.60 mol%. The highest relative density of the prepared ceramics was 91.31% and 87.23% for ceramics with 0.2 and 0.4 mol% content of doping respectively, this approached the theoretical density of ZnO (5.78 g/cm³). Microstructural characteristics were examined using SEM attached to EDX. The XRD patterns revealed primary phases of ZnO, with secondary phases including ZnSb₂O₄, Zn₇Sb₂O₁₂, MnVO₃, BiVO₄, and Zn₃(V₄)₂ polymorphs.