Microstructure and varistor properties of ZnO–V2O5–MnO2 ceramics with Ta2O5 addition

The effect of Ta2O5 addition on microstructure, electrical properties, and dielectric characteristics of the quaternary ZnO–V2O5–MnO2 vaistor ceramics was investigated. Analysis of the microstructure indicated that the quaternary ZnO–V2O5–MnO2–Ta2O5 ceramics consisted of mainly ZnO grain and minor secondary phases such as Zn3(VO4)2, ZnV2O4, TaVO5, and Ta2O5. As the amount of Ta2O5 increased, the sintered density increased from 94.8 to 97.2% of the theoretical density (5.78 g/cm3 for ZnO), whereas the average grain size decreased from 7.7 to 6.0 μm. The ceramics added with 0.05 mol% Ta2O5 exhibited the highest breakdown field (2715 V/cm) and the highest nonlinear coefficient (20). However, further increase caused α to abruptly decrease. The Ta2O5 acted as a donor due to the increase of electron concentration in accordance with the amount of Ta2O5. The donor concentration increased from 1.97×1018 to 3.04×1018cm−3 with increasing the amount of Ta2O5 and the barrier height exhibited the maximum value (0.95 eV) at 0.05 mol% Ta2O5.

► Quaternary ZnO–V2O5–MnO2–Ta2O5 ceramics have minor secondary phases such as Zn3(VO4)2, ZnV2O4, and TaVO5.
► Ta2O5 enhances the densification.
► Proper amount of Ta2O5 improves nonlinear properties.
► Ta2O5 acts as a donor.