Tungsten Oxide Ceramic

Tungsten oxide varistor ceramics refers to semiconducting ceramics in which the resistance value changes significantly with the applied voltage. It has non-linear volt-ampere characteristics. At a certain critical voltage, the resistance of the varistor ceramic is very high and there is almost no current. But when this threshold voltage is exceeded, the resistance will change drastically. And there is current through. With a little increase in voltage, the current will increase rapidly.

The sintering atmosphere has a great influence on the microstructure and electrical properties of tungsten oxide ceramics. Vacuum and atmosphere sintering in anoxic atmosphere can promote the production of more oxygen vacancies in the tungsten oxide ceramics, resulting in the increase of the spacing of the crystal planes in the crystal lattice and the diffraction peaks in the spectrum to move toward a small angle.

Oxygen vacancies can change the angle between tungsten and oxygen bonds in the tungsten oxide lattice. The main difference between several phase structures is the difference between the keys. This may be the reason why the tungsten oxide ceramics coexist at a room temperature or coexist in two phases. Oxygen atoms missing in the tungsten oxide ceramic are not supplemented when sintered in an oxygen-deficient atmosphere. Making tungsten oxide ceramic grain growth and densification is inhibited. Oxygen vacancies generated by tungsten oxide make the conductivity higher, making it conductive behavior in line with Ohm's law. The second sintering of the tungsten oxide ceramic sintered in an oxygen-deficient atmosphere is further performed in an atmosphere of air or oxygen, and the crystal grains of the tungsten oxide ceramic can be regrown.

In this process, the oxygen adsorbed by the grain boundary is combined with the electrons in the tungsten oxide ceramic to form a depletion layer of a certain width. That is, the Schottky barrier is formed at the grain boundaries to make the tungsten oxide ceramics appear pressure-sensitive. The oxidized tungsten ceramic samples obtained by sintering in an oxygen-deficient atmosphere and then placed in air or oxygen atmosphere for the second time, the varistor significantly increases, the leakage current decreases, and the nonlinear coefficient increases.

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