Modulating the Hysteresis of an Electronic Transition: Launching Alternative Transformation Pathways in the Metal-Insulator Transition of Vanadium(IV) Oxide
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2017 American Chemical Society. 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.
