Tungsten trioxide (WO3) is an emerging semiconductor material, with a growing number of energy-related applications in Li-ion batteries, photocatalysis, gas sensors and electrochromic devices. As an electrochromic material, WO3 turns from transparent to blue upon doping with monovalent species (e.g., H and Li), accompanied by a drop in transmittance in the near-IR. Due to it having an empty A-site in the ABO3 perovskite structure, high doping concentrations are possible through intercalation, making the properties of WO3 highly tunable. Tungsten trioxide has been experimentally shown to transform from the ground-state monoclinic symmetry to cubic symmetry with increasing monovalent doping .
We use first-principles calculations to understand this transformation. First, we describe the phase transformations and structural distortions. Our calculations show that the addition of electrons to the conduction band is a primary driver of the phase transformation. We next quantify the energetics and structural aspects of this transformation using density functional theory, allowing us to elucidate the mechanism. Comparison with experiment, role of the dopant species as defects, and implications of structural changes and doping on electronic and optical properties for device applications will be discussed.
 Q. Zhong, J. Dahn, K. Colbow. Phys. Rev. B 46 2554 (1992).