Varistor performance of a SnO2-based system doped with low content of SrTiO3

Abstract

The search and design of new SnO2-ceramics with non-linear current-voltage behavior is quite an important task due to the possibility of their practical application as varistors, devices for the protection of electrical circuits against voltage surges. This work reports the doping impact of the low content of SrTiO3 (0, 0.05, 0.1, 0.2, and 0.4 mol%) on the microstructure and non-ohmic properties of the SnO2-Co3O4-Cr2O3-Nb2O5 system which is frequently used in varistor design. It is found that the SrTiO3-addition results in the increase of activation energy of electrical conduction and the decrease of the leakage current in obtained materials compared with undoped ceramics. The reported materials with SrTiO3-addition possess a smaller average grain size, higher porosity, and their density is lower than that of unmodified SnO2-Co3O4-Cr2O3-Nb2O5 ceramics. The highest non-linear coefficient (α = 17.24) is observed for material with 0.05 mol% SrTiO3 while for undoped ceramics it reaches only 2.68. Energy dispersive spectroscopy (EDS) revealed agglomeration of SrTiO3 which was observed in materials with 0.1–0.4 mol% of SrTiO3. The obtained results are discussed in terms of the known barrier model for varistors based on the information from dc and ac electrical measurements, scanning electron microscopy, X-ray diffraction patterns, and EDS-data.