Tungsten Oxide Ceramics Varistor Performance

In 1994, it was first discovered that doped tungsten oxide varistors have varistor properties. Due to the lower varistor voltage, the varistor characteristics of tungsten oxide attract attention. Later, the effects of alumina and other dopants on the pressure sensitive properties were reported. However, the varistor characteristics of tungsten oxide varistor ceramics are extremely unstable, such as poor reproducibility of electrical behavior and negative resistance behavior, and the nonlinear coefficient is much smaller than that of zinc oxide. Therefore, there are few reports on tungsten oxide varistor ceramics in foreign countries, but there are many reports on the use of tungsten oxide varistors in gas sensors.

The domestic research on varistor tungsten oxide varistor ceramics is mainly doped to improve the nonlinear coefficient of varistor tungsten oxide varistor ceramics. However, the rare earth elements, alkali metal elements, divalent metal elements, and excessive element doping cannot improve the nonlinearity of the tungsten oxide varistor ceramic as they do. Some even lower their pressure-sensitive properties. Since tungsten oxide varistor ceramics are not doped, they also have pressure sensitive properties. It provides a relatively uncomplicated defect environment for the study of the grain boundary barrier model.

The main research now is to establish a mechanism model for pressure-sensitive characteristics and to improve the pressure-sensitive characteristics of oxygen based on the model. The tungsten oxide grain boundary potential barrier is the generation and migration of non-equilibrium defects in the tungsten oxide varistor ceramic during and after cooling. This is followed by the formation of a high-resistivity layer on the surface of the grains under the effect of oxygen adsorption.

Due to the large difference in resistance inside and outside the grain, tungsten oxide varistor ceramics can produce non-linear electrical properties. The pressure-sensitive characteristics decrease as the holding time of the tungsten oxide varistor ceramic increases during the high temperature phase. A corollary of its model is that the grain surface should be more highly oxidized with increasing holding time. At the same time, the resistance difference between the inside and outside of the grain should be greater, and the pressure sensitive characteristics should be more pronounced.

• < Prev
• Next >