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.

Because of the larger radius of oxygen atoms, poor mobility. Therefore, in the sintering process of oxide ceramics, the transmission rate of oxygen atoms determines the sintering performance of tungsten oxide ceramics.

The graph below shows the volt-ampere characteristics of tungsten oxide ceramics sintered at different holding temperatures. The electrical non-linear behavior of varistors typically occurs at current densities in the region of 1-10 mA. From the figure we can see that at 1050 ℃ 1100 ℃ and insulation for two hours of tungsten oxide ceramics, in the current density of 1-10mA region has a non-linear volt-ampere curve. That is, the pressure sensitive characteristics are exhibited.

The figure is a diagram of tungsten oxide ceramics sintered at different holding temperatures. Since the crystal structure of tungsten oxide ceramics is very complicated, we narrow down the scanning angle to 20-30 ° to observe the change of the triple peak of tungsten oxide ceramics. From the figure, we can see that the crystal structure of the tungsten oxide ceramic does not change substantially when it is sintered at a temperature of 900-1000°C. However, the XRD peak of the tungsten oxide ceramic moves to a small angle when sintering at a temperature of 1050-1100°C, and the blue shift occurs.

It can be clearly seen from the figure that as the soaking temperature increases, the grain size of the tungsten oxide ceramic increases. When the holding temperature is 900-1000°C, there are many small-sized grains in the sample. When the holding temperature is 1050-1150 ℃, the small grains in the tungsten oxide ceramics disappear, and the grains increase obviously. Also found at 1150 ℃ insulation tungsten oxide ceramics, although the larger grain size. However, its porosity is also significantly increased, the densification of tungsten oxide ceramics worsened.