Electrical Properties at Grain Boundaries Influenced by Cr³⁺Diffusion in SnO₂.ZnO.Nb₂O₅-Films Varistor Prepared by Electrophoresis Deposition

Abstract

SnO 2 -based varistors are strong candidates to replace the ZnO-based varistors due to ordering fewer additives to improve its electrical behavior as well as by showing similar nonlinear characteristics of ZnO varistors. In this work, SnO 2 -nanoparticles based-varistors with addition of 1.0 %mol of ZnO and 0.05 %mol of Nb 2 O 5 were synthesized by chemical route. SnO 2 .ZnO.Nb 2 O 5 -films with 5 μm of thickness were obtained by electrophoretic deposition (EPD) of the nanoparticles on Si/Pt substrate from alcoholic suspension of SnO 2 -based powder. The sintering step was carried out in a microwave oven at 1000 °C for 40 minutes. Then, Cr 3+ ions were deposited on the films surface by EPD after the sintering step. Each sample was submitted to different thermal treatments to improve the varistor behavior by diffusion of ions in the samples. The films showed a nonlinear coefficient (α) greater than 9, breakdown voltage (V R ) around 60 V, low leakage current (