Epitaxial stabilization and phase instability of VO2 polymorphs

TL;DR

This study successfully synthesizes and stabilizes various VO2 polymorphs as high-quality thin films, revealing their distinct properties and phase stability, which paves the way for advanced electronic and energy applications.

Contribution

It demonstrates the epitaxial stabilization of all VO2 polymorphs, including rarely studied phases, and investigates their phase stability and physical properties.

Findings

Distinct physical properties of VO2 polymorphs identified

VO2 polymorphs can undergo phase transitions at ~400°C

Epitaxial growth enables phase-pure VO2 polymorphs

Abstract

The VO2 polymorphs, i.e., VO2(A), VO2(B), VO2(M1) and VO2(R), have a wide spectrum of functionalities useful for many potential applications in information and energy technologies. However, synthesis of phase pure materials, especially in thin film forms, has been a challenging task due to the fact that the VO2 polymorphs are closely related to each other in a thermodynamic framework. Here, we report epitaxial stabilization of the VO2 polymorphs to synthesize high quality single crystalline thin films and study the phase stability of those metastable materials. We selectively deposit all the phases on various perovskite substrates with different crystallographic orientations. By investigating the phase instability, phonon modes and transport behaviours, not only do we find distinctively contrasting physical properties of the VO2 polymorphs, but that the polymorphs could be on the verge of phase transitions when heated as low as ~400 oC. Our successful epitaxy of both VO2(A) and VO2(B) phases, which are rarely studied due to the lack of phase pure materials, will open the door to the fundamental studies of VO2 polymorphs for potential applications in advanced electronic and energy devices.