Electrical properties of tin oxide based varistors with PbO addition in humid air

In order to decrease the humidity sensitivity of SnO2–Co3O4–Nb2O5–Cr2O3 varistor ceramics, lead oxide was added and the electric characteristics of synthesized materials with the PbO concentration of 0, 0.1, 0.5, 0.7, 1 and 2 mol.% in the air with relative humidity of 10–86% were investigated. All tested samples have non-linear current–voltage characteristics with large values of the nonlinearity coefficient of 38–51. The optimal concentration of PbO addition in ceramics is 0.5–0.7 mol.%. The addition of such quantity of lead oxide to the ceramics leads to the decrease of the breakdown electric field up to 4390 V/cm and the humidity sensitivity coefficient up to 172. The increase of the PbO concentration provides the increase of the electrical conductivity of samples at low fields. The barrier mechanism of electrical conductivity of the studied ceramics is proved by the obtained values of potential barrier heights of 0.85–0.90 еV on the SnO2 crystallite boundaries.