Chromism in Ferroelectric ε-WO₃: Single-Layer Solid-State Color-Changing Devices and Displays

WO3 is well known for its electrochromic γ and hexagonal phases, which are used to produce inorganic electrochromic devices (ECDs). This study explores a phenomenon observed in the ferroelectric ε-WO3 polymorph, which we have named ferroelectric chromism. Evidence presented here supports the claim that the ferroelectric nature of ε-WO3 plays a key role in the color change observed upon the application of the electric potential to this material. A mechanism for the observed ferroelectric color changing effect is provided in this study as elucidated by X-ray photoelectron spectroscopy analysis. As coloration appears in a single solid-state layer of ε-WO3 by this chromic effect, developing the next generation of ECDs is possible using this ferroelectric polymorph of WO3.