Influence of Cr2O3 on highly nonlinear properties and low leakage current of ZnO–Bi2O3 varistor ceramics

Abstract ZnO–Bi 2 O 3 –Sb 2 O 3 –Co 2 O 3 –MnO 2 – x Cr 2 O 3 (ZBSCM– x Cr 2 O 3 , 0≤ x ≤0.6 mol%) varistors were fabricated through the conventional solid state method, and the effects of Cr 2 O 3 on the microstructures and electrical properties were investigated. Results showed that the secondary phases CrBi 18 O 30 and Co 2 Cr 0.5 Sb 0.5 O 4 emerged when x ranges from 0.2 to 0.4. In these compositions, Cr 2 O 3 acted as a donor and decreased the electrical properties of ZBSCM. For samples with x =0.5, the secondary phases transformed to MnCr 2 O 4 and the electrical properties increased significantly: the nonlinear coefficient α sharply increased up to 80.71 and the barrier height ϕ b reached 3.88 eV. This indicates that the donor effect of Cr 2 O 3 disappeared. In addition, with the increase of Cr 2 O 3 , the average grain size of ZnO decreased from 7.48 μm to 5.46 μm, which in turn resulted in an increase of breakdown voltage E 1mA from 216.17 V/mm to 362.50 V/mm. Besides, all the samples showed the low value of leakage current of lower than 0.1 μA. This varistor might be a promising candidate for highly effective applications.