Two stage sintering behaviour of Er2O3 doped high performance ZnO varistors

High performance Er₂O₃ doped ZnO-V₂O₅ based varistors were prepared by two stage sintering (TSS) method at T₁ = 1050 °C for 1/6 h and T₂ = 750 and 800 °C for 2.5, 10, 20 and 40 h duration. The microstructural features and electrical properties were studied by XRD, SEM, EDS and a high voltage source unit. The combined effect of TSS and Er₂O₃ doping is very beneficial to restrain the grain coarsening of varistors. The effect of grain size reduction on nonlinear electrical properties was investigated. The results showed that superior electrical properties were obtained in doped samples via TSS than single stage one. A typical fine-grained (1.7 μm, 97.5 %TD) varistor with sufficiently high nonlinear exponent (α = 154), breakdown field (E_B = 15.2 kV cm^?1) and reasonably low leakage current density (J_L = 0.13 mA cm^-2) could be prepared with 0.5 mol.% Er₂O₃ doping at an optimum sintering condition of T₁/T₂ = 1050/750 °C for 40 h.