Switching VO2 Single Crystals and Related Phenomena: Sliding Domains and Crack Formation

Abstract

VO2 is the prototype material for insulator–metal transition (IMT). Its transition at TIMT = 340 K is fast and consists of a large resistance jump (up to approximately five orders of magnitude), a large change in its optical properties in the visible range, and symmetry change from monoclinic to tetragonal (expansion by 1% along the tetragonal c-axis and 0.5% contraction in the perpendicular direction). It is a candidate for potential applications such as smart windows, fast optoelectronic switches, and field-effect transistors. The change in optical properties at the IMT allows distinguishing between the insulating and the metallic phases in the mixed state. Static or dynamic domain patterns in the mixed-state of self-heated single crystals during electric-field induced switching are in strong contrast with the percolative nature of the mixed state in switching VO2 films. The most impressive effect—so far unique to VO2—is the sliding of narrow semiconducting domains within a metallic background in the positive sense of the electric current. Here we show images from videos obtained using optical microscopy for sliding domains along VO2 needles and confirm a relation suggested in the past for their velocity. We also show images for the disturbing damage induced by the structural changes in switching VO2 crystals obtained for only a few current–voltage cycles.

Investigating Metal–Insulator Transition and Structural Phase Transformation in the (010)-VO2/(001)-YSZ Epitaxial Thin Films

“…This amplitude of MIT is comparable with the cases of the VO 2 /Al 2 O 3 and VO 2 /TiO 2 epitaxial thin films [ 21 , 26 ]. Additionally, the temperature of MIT is about 342 K in the heating cycle, which is consistent with the temperature of 340 K for the bulk VO 2 [ 27 ]. It is known that the VO 2 is an n -type semiconductor in the insulating phase (M1).…”

Magnetic irreversibility in VO2/Ni bilayers

“…The irreversibility observed in the VO 2 R versus T characteristics may be attributable to the formation of nanoscale cracks as VO 2 goes through its SPT [29][30][31][32][33][34][35][36]. Cracks have been observed in VO 2 single crystals as well as in thin films [37][38][39]. During the heating process, cracks form as a method of thermal stress relaxation.…”

Elucidating the Crystallite Size Dependence of the Thermochromic Properties of Nanocomposite VO2 Thin Films

“…The pronounced near-room-temperature metal–insulator transition of VO 2 provides a means to modulate solar heat gain in a spectrally selective manner. Nanocrystals provide distinct advantages over continuous thin films in being able to better accommodate strains arising from thermal cycling and in affording a higher visible-light transmittance, mitigating the thermal-cycling-induced pulverization of large crystals. , However, the use of nanocrystals requires elucidation of optimal crystallite dimensions, refractive-index matching, and the appropriate dispersion of the nanocrystals within a low-refractive-index medium. EMA and FEA + GO optical simulations indicate a pronounced size dependence of the visible-light transmittance for VO 2 nanocomposite thin films.…”