Tungsten Trioxide Crystal Structure

Yellow tungsten oxide (YTO), an oxide of tungsten, with a yellow powder appearance and a chemical formula of WO₃, it is an important chemical raw material in the history of tungsten smelting in China.

The crystal structure of WO₃ is more complex, a very significant characteristic is often the existence of distortion and the oxygen vacancy in different degrees. People usually use WO₃-y as there are different degrees of WO₃ crystal molecular oxygen vacancy type. As the number of oxygen vacancies increases, their distribution in the crystal becomes orderly, forming the so-called shear surface. Some foreign scholars have used neutron powder diffraction technology to make detailed measurements on the triclinic structure of WO₃. The monoclinic and triclinic phases of WO₃ are the same except for the different projection. In both crystal phases, all of the tungsten atoms are displaced in the same way from their position in the octahedron to one side of the octahedron. Thus, each tungsten atom has two short, two medium and two long oxygen bonds. The average length of the tungsten-oxygen bond is essentially the same for both phases.

On the other hand, tungsten trioxide undergoes at least five structural phase transitions in a temperature range of 40 °C to 740 °C, and the corresponding crystal structures appear as follows: There are also hexagonal tungsten trioxide crystals in the low temperature monoclinic (α-W0₃) room temperature monoclinic (β-W0₃) phase and the tetragonal phase (α-W0₃) phase. These different structural transitions are not the recombination of tungsten atoms and oxygen atoms, but are caused by distortion and distortion of tungsten atoms in the original ideal crystal structure, these phase transitions from low to high temperatures indicate that stable phases of tungsten trioxide formed at high temperatures are also stable at low temperatures.

Therefore, by studying the crystal structure of tungsten trioxide, it can be found that the phase transition of tungsten trioxide does not depend solely on the temperature but also on other factors such as the grain size. This makes tungsten trioxide promising in the field of photo-induced densification, photocatalysis and gas-sensitive materials.

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