Modulating the Hysteresis of an Electronic Transition: Launching Alternative Transformation Pathways in the Metal–Insulator Transition of Vanadium(IV) Oxide

Materials exhibiting pronounced metal–insulator transitions such as VO₂ have acquired great importance as potential computing vectors and electromagnetic cloaking elements given the large accompanying reversible modulation of properties such as electrical conductance and optical transmittance. As a first-order phase transition, considerable phase coexistence and hysteresis is typically observed between the heating insulator → metal and cooling metal → insulator transformations of VO₂. Here, we illustrate that substitutional incorporation of tungsten greatly modifies the hysteresis of VO₂, both increasing the hysteresis as well as introducing a distinctive kinetic asymmetry wherein the heating symmetry-raising transition is observed to happen much faster as compared to the cooling symmetry-lowering transition, which shows a pronounced rate dependence of the transition temperature. This observed kinetic asymmetry upon tungsten doping is attributed to the introduction of phase boundaries resulting from stabilization of nanoscopic M₂ domains at the interface of the monoclinic M₁ and tetragonal phases. In contrast, the reverse cooling transition is mediated by point defects, giving rise to a pronounced size dependence of the hysteresis. Mechanistic elucidation of the influence of dopant incorporation on hysteresis provides a means to rationally modulate the hysteretic width and kinetic asymmetry, suggesting a remarkable programmable means of altering hysteretic widths of an electronic phase transition.