Effect of oxidizing and reducing atmospheres on the electrical properties of dense SnO2-based varistors

• Published in: Journal of the European Ceramic Society Vol. 21; no. 2; pp. 161 - 167
• Main Authors: SANTOS, Maria R. C, BUENO, Paulo R, LONGO, Elson, VARELA, José A
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier 01.02.2001
• Subjects: Applied sciences; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Conductivity of specific materials; Conductors, resistors (including thermistors, varistors, and photoresistors); Electronic equipment and fabrication. Passive components, printed wiring boards, connectics; Electronic transport in condensed matter; Electronics; Exact sciences and technology; Physics; Grain boundaries; Varistors; Inorganic compounds; Electrical properties; Transition element compounds; Tantalum oxides; Controlled atmospheres; Cobalt oxides; Reducting atmosphere; Experimental study; Oxidizing atmosphere; Tin oxides; Chromium oxides; Microstructure; IV characteristic
• ISSN: 0955-2219; 1873-619X
• DOI: 10.1016/S0955-2219(00)00177-1

SnO2-based varistor systems have a promising potential in commercial applications. Experimental evidence shows that there is a dependence of nonlinear constant values with thermal treatment under different atmospheres. Thermal treatments in oxygen and nitrogen rich atmospheres at 900C prove this dependence, indicating that the nonlinear constant values are significantly lower when the material is submitted to a nitrogen atmosphere. Moreover, electrical properties can be restored when the varistor is subjected to thermal treatment at the same temperature in an oxygen atmosphere, indicating that the mechanism seems to be reversible. This behaviour is discussed focusing on the grain boundary region. Ta2O5 mol% additive concentrations were also analysed and the results indicate an optimum Ta2O5 concentration of 0.05 mol% for the electrical properties (alpha = 44 and EB = 6150 V/cm). 42 refs.