Theoretical Study on the Structures and Electronic Properties of Tungsten Fluorides at High Pressures.

Transition metal fluorides are a series of strong oxidizing agents. Tungsten (W) fluorides, particularly WF 6 , have shown broad applications such as luminescence and fluorinating agent. However, other stoichiometries of W fluorides have rarely been studied. It is well-known that pressure can induce structural phase transition, stabilize new compounds, and produce novel properties. In this work, the high-pressure phases of W-F were searched systematically at the pressure range of 0-200 GPa through first-principles swarm-intelligence structural search calculations. A new stoichiometry of WF 4 has been predicted to be stable under high pressures. On the other hand, two new high-pressure phases of WF 6 with the symmetries of P 2 1 ${{P2}_{1}}$ /m and P ${P}$ -1 were found with decahedral structural units. The electronic properties of the W-F compounds were then investigated. The predicted stable WF 6 high-pressure phases maintain semiconducting features, since the W atom provides all its valence electrons to fluorine. We evaluated the oxidizing ability of WF 6 by calculating its electron affinity potential. The high pressure P 2 1 ${{P2}_{1}}$ /m WF 6 molecular phase shows higher oxidation capacity than the ambient phase. The built pressure-composition phase diagram and the theoretical results of W-F system provide some useful information for experimental synthesis.