Bi-Er-O pre-synthesized phase (Bi1-xErx)2O3 doped ZnO varistors with high nonlinear coefficient and low leakage current

The content of free oxygen O-ad at the ZnO grain boundaries has an important impact on the double Schottky barrier and electrical properties of ZnO varistors. In this work, Bi-Er-O pre-synthesized (BE) phase (Bi1-xErx)(2)O-3 (0.25 < x < 0.455) with high conductivity of O-ad was prepared using Bi2O3 and Er2O3 as raw materials, and the effects of the BE phase doping on the phase, grain boundary properties, and electrical properties of ZnO-Bi2O3-Sb2O3-Co2O3-MnO2-Cr2O3-SiO2 varistors were studied. XRD analysis shows that the lattice constant of the BE phase (Bi1-xErx)(2)O-3 is between (Bi0.75Er0.25)(2)O-3 and BiErO3. With increasing doping content of the BE phase from 0 to 0.75 wt%, part of Er3+ still exists in the form of the BE phase (Bi1-xErx)(2)O-3 at the ZnO grain boundaries, and its content increases with increasing doping content of the BE phase. The conductivity of O-ad in (Bi1-xErx)(2)O-3 is much higher than that in Bi2O3, resulting in the generation of a large number of negative O ' and O '' at the ZnO grain boundaries, and decreasing concentration of the intrinsic point defect zinc interstice Zn-i. So the donor concentration N-d decreases, the height of the grain boundary barrier increases, the depletion layer widens, and the electrical properties are improved. By analyzing the low-temperature permittivity spectra, it was calculated that with increasing doping content of the BE phase from 0 to 0.75 wt%, the concentration of oxygen vacancy V-O(center dot) decreases inappreciably, but the concentration of zinc interstice Zn-i(center dot center dot) decreases by about 23%. When the doping amount of the BE phase is 0.75 wt%, the nonlinear coefficient alpha of the obtained ZnO varistors is 73.9 +/- 0.6, and the leakage current density J(L) is only 0.3 +/- 0.1 mu A/cm(2). This study provides an important reference for improving the electrical properties of ZnO varistors by manipulating the Bi-rich phase structure to improve the double Schottky barrier characteristics.