Insulator to Metal Transition in WO$_3$ Induced by Electrolyte Gating

TL;DR

This study demonstrates that electrolyte gating can induce an insulator-to-metal transition in WO$_3$ films through hydrogen intercalation, significantly altering their electrical properties.

Contribution

It reveals hydrogen intercalation as the doping mechanism behind the transition, advancing understanding of electrochemical control in transition metal oxides.

Findings

Resistivity of WO$_3$ films changed by over five orders of magnitude.

Insulator-to-metal transition observed via electrolyte gating.

Hydrogen intercalation identified as the doping mechanism.

Abstract

Tungsten oxide and its associated bronzes (compounds of tungsten oxide and an alkali metal) are well known for their interesting optical and electrical characteristics. We have modified the transport properties of thin WO$_3$ films by electrolyte gating using both ionic liquids and polymer electrolytes. We are able to tune the resistivity of the gated film by more than five orders of magnitude, and a clear insulator-to-metal transition is observed. To clarify the doping mechanism, we have performed a series of incisive operando experiments, ruling out both a purely electronic effect (charge accumulation near the interface) and oxygen-related mechanisms. We propose instead that hydrogen intercalation is responsible for doping WO$_3$ into a highly conductive ground state and provide evidence that it can be described as a dense polaronic gas.