研究目的
To review the literature on the new varistor ceramic composition based on tungsten oxide (WO3), focusing on how structural and electrical properties of these systems vary with and without doping of metal oxides, as well as the type of thermal treatment used and the atmosphere in which the material was sintered.
研究成果
Unlike varistors based on SnO2, ZnO, and TiO2, the varistor based on WO3 presents non-linear behavior when pure due to the phases formed during sintering. These phases are also responsible for the non-linearity of doped systems, sometimes presenting an abnormal negative resistance behavior. The mechanism of non-linearity of WO3 varistors can be explained by the presence of defects responsible for the formation of the Schottky-type potential barrier and by oxygen species adsorbed at the grain boundary.
研究不足
The non-linearity coefficients obtained in all the studied systems are still low, although the breakdown electric fields indicate an application in low voltage.