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 VO<sub>2</sub> 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 VO<sub>2</sub>. Here, we illustrate that
substitutional incorporation of tungsten greatly modifies the hysteresis
of VO<sub>2</sub>, 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 M<sub>2</sub> domains at
the interface of the monoclinic M<sub>1</sub> 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