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 Cr 3+ , Y 3+ or Ho 3+ 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

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... prevent poor densification. The obtained optimal samples with a diameter of about 14 mm have a nonlinear coefficient (α) of about 60, threshold electric field (Eb) of about 380 V/mm, and the withstanding peak current of 8/20 μs 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.