Studying Tungsten Trioxide Structural Phase Transition Law

Structural phase transition region is divided into two basic types: remodeling and displacement type. Such classification is based on the grid by the formation of chemical bonds through periodic phase change. Strictly speaking, the non-reconstruction-type structural phase transitions are classified as displacement. Obviously, this is difficult to include atoms, molecules, cells and equivalent groups in a deep potential. For the reconstruction phase transition, we can include structural changes in carbon, graphite and diamond, which including the reconstruction phase transition and displacement phase transition, order - disorder phase transition, hybrid phase transition, and electron-phonon interaction associated phase transition. Of course, it does not include the superconducting phase transition, because its system structure.

Structure of tungsten trioxide can be described as WO₆ octahedron vertices that sharing three-dimensional network structure, however, WO₃ symmetry is relatively low, because it is deformed over ReO₃ structure. The lattice phonons and electronic structure of the combined effect of the changes is produced by several crystalline phases, these types of crystalline phases are the evolution from low to high symmetry with increasing temperature.

By studying the structure of the tungsten trioxide phase transformation, the phase change can be found in its crystalline order: monoclinic Pc (ε- WO₃)→triclinic PT (ζ- WO₃)→orthogonal Pbcn (β- WO₃)  →quartet P4 / ncc (α- WO₃) → P4 / nmm, which presents different phase ramp in a different reaction temperature. In 2002, we found a new crystalline phase by continuous research. The high resolution neutron powder diffraction method confirms the existence of a new monoclinic phase at a temperature region of 720 ℃ to 790 ℃.

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