Structural and electronic properties of tungsten oxides under high pressures.

Tungsten (W) oxides have shown broad applications such as photocatalyst and cathode of lithium ion batteries. It is well-known that pressure can induce structural phase transition, producing novel properties. On the other hand, the study of W oxides under high pressures is beneficial for the control of the oxygen fugacity. In this work, we built the high-pressure phase diagram of W-O binary compounds through first-principles swarm-intelligence structural search calculations. WO2 and WO3 are stable in the whole considered pressure range from 0 to 300 GPa. Besides reproducing the known structures, we identify two new phases of WO2 (e.g. C2/m and Cmca) and three ones for WO3 (e.g. Pnma, Cmcm, and Pm-3n), associating with the evolution of polyhedron (i.e. octahedron  →  distorted octahedron for WO2, and octahedron  →  hendecahedron  →  tetradecahedron  →  icosahedron for WO3). More interestingly, the Pm-3n-structured WO3 shows the highest coordination number of 12. Electron structure calculations indicate that pressure-induced nonmetal  →  metal transition occurs for WO2 and WO3. Our study provides an opportunity to understand the structures and electronic properties of W-O system under high pressure.