Tungsten Oxide Rare-Earth Doping

Rare-earth doping methods can affect the microstructure, phase structure, nonlinear electrical properties, and dielectric properties of tungsten oxide. According to related studies, the main conclusions of the influence of rare earth doping on tungsten oxide are:

（1）Rare-earth doping affects the growth of tungsten oxide grains. A small amount of doping of gallium and germanium limits grain growth, and large amounts of doping can promote grain growth. Doping with germanium and antimony can promote the growth of tungsten oxide grains. Gallium doping can inhibit the growth of tungsten oxide grains. The grain size of the sample is basically between 10 and 20μm. The energy spectrum analysis showed that the dopants mainly segregated at the grain boundaries.

（2）Rare-earth doping can significantly suppress the formation of triclinic tungsten oxide, which makes tungsten oxide single phase, and thus improves the electrical stability of tungsten oxide ceramics under high electric field. Rare earth doping can reduce ion mobility in the depletion layer, making the sample also have stable electrical properties at low electric fields. This shows that tungsten oxide has a good application prospect in the low voltage area.

（3）Rare-earth-doped tungsten oxide ceramics have a low varistor voltage and barrier voltage, so tungsten oxide is particularly suitable for low-voltage varistors.

（4）Rare-earth doping does not increase the nonlinear coefficient of tungsten oxide ceramics. The nonlinear coefficient is basically within 2-5.

（5）Rare-earth doping can increase the dielectric constant of tungsten oxide to a certain degree, and can be increased by about one order of magnitude. The increase in dielectric constant makes tungsten oxide more suitable for capacitive-pressure-sensitive bifunctional materials.

（6）The samples doped with scandium and yttrium have a special grain boundary phase and a porous material appears at grain boundaries in the scandium-doped sample. This material is less conductive and forms the Schottky barrier. Therefore, the sample exhibits nonlinear voltammetry characteristics. A bar-like material appears at the grain boundary of the germanium-doped sample. This rod-like material has good conductivity, so that the barrier between crystal grains disappears. The sample therefore exhibits linear volt-ampere characteristics. The grain boundary resistance and grain resistance of the antimony-doped sample are not much different. However, it still has a large dielectric constant. This shows that the conventional grain boundary layer barrier capacitor model does not explain the phenomenon of high dielectric constant of the doped sample.

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