The ion migration process and cyclic stability of voltage-induced vanadium dioxide phase transition

Abstract

The metal-to-insulator transition (MIT) of vanadium dioxide (VO₂) has been widely researched. However, the high phase transition temperature (PTT) and the single thermal phase transition severely limit its application. Hereby, the dynamic phase transition of VO₂ with a thermal–electrical dual response was achieved by voltage-induced ion gating. Unfortunately, the stability of ion migration is affected by ion capture, which greatly reduces the VO₂ phase transition capability. In this work, we introduced a LiF layer, which improved the cyclic stability due to the following two reasons. Firstly, the VO₂ film would not fall off with the support of the high modulus and electrochemically stable LiF layer. Secondly, the barrier of a low diffusion rate for Li⁺ induced the ordered and rapid migration of Li⁺ in the grain boundaries of LiF uniformly, which effectively restricted the accumulation of Li⁺ in the VO₂ lattice. As a result of the contribution of these two factors, the cyclic stability can reach up to 50 cycles. Moreover, the gating time just only needs 2.5 min for the phase transition, which was shorter than proton gating (over 60 min). This study provides a stable, dual-response VO₂ composite film and also could be guidance for some potential applications in smart windows.