David Cobden, UW Physics
The phase diagram of vanadium dioxide
The metal-insulator transition (MIT) in vanadium dioxide is a candidate for numerous optical and electrical switching applications. However, it is a first-order solid-state phase transition, making it notoriously challenging to study reproducibly in any detail. The combination of the change in unit cell shape, the long range of elastic distortion, and latent heat, leads to domain structure, hysteresis, and cracking of even the highest quality samples. It is known that at the MIT two or more insulating phases (M1 and M2) occur in addition to the metallic phase (R), but the phase diagram relating these phases was not known. To determine it we studied single-crystal nanobeams of VO2 in a purpose-built nanomechanical strain apparatus. We were able to measure the transition temperature accurately for the first time to be 65.0 ± 0.1 °C, and found the surprising and suggestive result that the transition occurs precisely at the solid-state triple point of the metallic and two insulating phases.