Sub-stoichiometric Tungsten Oxide

Sub-stoichiometric tungsten oxide (WO_3-x) is a tungsten oxide structure containing many oxygen defects in the crystal lattice. Partial depletion of oxygen in tungsten oxide affects its electron band structure and increases its conductivity. Tungsten oxide reduction reaction is usually accompanied by structural changes.

Some common sub-stoichiometric tungsten oxides are WO_2.9, WO_2.83, WO_2.72 and the like. These structures are alternately formed by the tungsten oxide octahedron common corners or common sides and oxygen atoms are eliminated by the crystal shear mechanism. As x increases, the co-edge tungsten oxide octahedra form a shear plane pocket, and when x is close to 0, these shear planes are extended defects if they are in an isolated or disordered state.

For tungsten oxide, the electrical and optical properties of tungsten oxide are controlled by local electrons including polaron when 0 <x <0.1. The quasiparticles consist of carriers and polarized fields in the lattice. When x = 0.1, the tungsten oxide undergoes a metal-insulator transition and the local polarization wave functions begin to overlap and form a delocalized state. When x> 0.1, the electrical and optical properties of tungsten oxide are controlled by free electrons. Unlike the yellow of tungsten oxide, an extra broad absorption peak appears between 480 and 700 nm. Tungsten oxide is light green. And this additional absorption peak is due to the existence of oxygen vacancies in the conduction band under the new discrete energy band caused. In addition, tungsten oxide shows light absorption in the near-infrared region comparable to that of bandgap absorption due to the induction of local surface plasmon resonance.

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