Contact-Free Electrical Measurements of VO2 Powder

Vanadium dioxide (VO$_{\mathrm{2}})$ is a strongly correlated transition metal oxide with a metal-insulator transition at 67o C (in bulk). Researchers have often attempted to manipulate this transition through electrochemical gating, doping, and other processes. Because strain can strongly affect the transition, we examine VO2 in comparatively strain-free powder form, though this is complicated by the difficulty of testing a powder's electronic properties. We study the transition by building small inductors and filling them with VO2 powder, then using an AC inductance bridge setup to test for changes in inductance proportional to identical, empty inductors. The resulting figures clearly show a transition at temperatures similar to those found experimentally in nanowires, though some of the more intricate details of the plots remain surprising. Notably, the inductance of the VO2 filled solenoid exhibits a peak when warming through the transition (rather than a step function change), and a dip upon cooling through the transition (again, rather than a step function change). We discuss these observations.