SnO2-based varistors capable of withstanding surge current

SnO2-based varistor material was fabricated by doping of CoO, Nb2O5, Cr2O3, and Y2O3 or Ho2O3. The microstructure, nonlinear I-V characteristic and surge current performances have been investigated. The average grain boundary voltage of the obtained materials is close to that of ZnO varistors. Similar to Cr3+, Y3+ or Ho3+ acts as the acceptor in the grain boundaries and the depletion layers. Moderate co-doping Y2O3 or HO2O3 with Cr2O3 is helpful to improve the electrical performances and to prevent poor densification. The obtained optimal samples with a diameter of about 14 mm have a nonlinear coefficient (alpha) of about 60, threshold electric field (E-b) of about 380 V/mm, and the withstanding peak current of 8/20 mu s wave is about 2400 A. Higher surge current will cause failure but no visual damage happen. This kind of failure mode is helpful for safety use of varistors. (C) 2009 The Ceramic Society of Japan. All rights reserved.