Tungsten Oxide Doped with Antimony and Tellurium

Both tantalum and tantalum doped tungsten oxide ceramics have relatively high dielectric constants. It is generally believed that there is a high-resistance insulating layer between the crystal grains and grains of these oxide ceramics, that is, a so-called grain boundary layer barrier capacitor, and therefore has a high dielectric constant.

In germanium-doped tungsten oxide, there is a barrier between grains and grains, so the dielectric constant of tungsten oxide can also be explained by the grain boundary layer barrier capacitor model. However, for the high-content doped samples, the grain boundary resistance is small and the potential barrier disappears, but they also have almost the same high dielectric constant. This obviously cannot be explained by the grain boundary layer barrier capacitor model.

This may be because: On the one hand, the germanium-rich phase in the grain boundary is a crystalline phase. This crystalline phase has a very strong dielectric polarization. On the other hand, a small portion of the doped germanium enters the tungsten oxide lattice, increasing the intrinsic dielectric constant of the tungsten oxide crystal. Tungsten oxide has a high dielectric constant. Both yttria and erbium doping can promote tungsten oxide grain growth.

In the germanium-doped tungsten oxide, a porous substance appears at grain boundaries. This material is less conductive and forms the Schottky barrier. Therefore, the sample exhibits nonlinear voltammetry characteristics. Rod-like substances appear at the grain boundaries of the cerium-doped samples. This rod-like substance has good conductivity, so that the barrier between crystal grains disappears. Therefore, tungsten oxide exhibits linear voltammetry characteristics. In different doped samples, the main crystalline phases are monoclinic tungsten oxide. Compared to cerium ions, cerium ions more easily enter the crystal lattice of tungsten oxide. As a result, the tungsten oxide crystal lattice expands. Both doping and antimony doping can significantly increase the dielectric constant of tungsten oxide ceramics. The grain boundary resistance and grain resistance of the antimony-doped samples are not much different, but they still have a large dielectric constant. This shows that the conventional grain boundary layer barrier capacitor model does not explain well the fact that germanium-doped tungsten oxide has a high dielectric constant.

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