Decoupling the metal insulator transition and crystal field effects of VO2

Abstract

VO2 is a highly correlated electron system which has a metal-to-insulator transition (MIT) with a dramatic change of conductivity accompanied by a first-order structural phase transition (SPT) near room temperature. The origin of the MIT is still controversial and there is ongoing debate over whether an SPT induces the MIT and whether the Tc can be engineered using artificial parameters. We examined the electrical and local structural properties of Cr- and Co-ion implanted VO2 (Cr-VO2 and Co-VO2) films using temperature-dependent resistance and X-ray absorption fine structure (XAFS) measurements at the V K edge. The temperature-dependent electrical resistance measurements of both Cr-VO2 and Co-VO2 films showed sharp MIT features. The Tc values of the Cr-VO2 and Co-VO2 films first decreased and then increased relative to that of pristine VO2 as the ion flux was increased. The pre-edge peak of the V K edge from the Cr-VO2 films with a Cr ion flux ≥ 1013 ions/cm2 showed no temperature-dependent behavior, implying no changes in the local density of states of V 3d t2g and eg orbitals during MIT. Extended XAFS (EXAFS) revealed that implanted Cr and Co ions and their tracks caused a substantial amount of structural disorder and distortion at both vanadium and oxygen sites. The resistance and XAFS measurements revealed that VO2 experiences a sharp MIT when the distance of V–V pairs undergoes an SPT without any transitions in either the VO6 octahedrons or the V 3d t2g and eg states. This indicates that the MIT of VO2 occurs with no changes of the crystal fields.

Towards Unlocking/Tuning the Mott Transition Temperature in Alkaline-Doped Vanadium Oxide Thermochromic Coatings and Potential Green Air-Conditioning via Room Temperature VxOy-V-VxOy Layered Coatings

“…This substantial lowering of the TMIT, which is the second prominent finding of this study, is likely to be ascribed to the above-mentioned interfacial diffusion and/or stress or strain as well as the alkaline diffusing elements. This parameter was found to be pivotal in significantly affecting the crystallographic properties but mostly the corresponding electronic response in view of the electronic orbitals' configuration [48]- [51]. As a preliminary conclusion, one might consider with provision that the investigated V2O5/V/V2O5 stacks (with 7 and 12 nm V layer's thickness) onto the borosilicate glass substrate behave as a hypothetic thermochromic VxOy phase.…”

Dual Mode Optoelectronic Devices Based on 2D Single Crystalline VO2 Films with Controlled Metallic Domain Regime Induced Variable Hysteresis

“…In recent years, vanadium dioxide (VO 2 ) has emerged as one of the most promising multifunctional materials because it undergoes a metal‐insulator transition (MIT), accompanied by a crystallographic phase transition from the tetragonal rutile (R) to monoclinic (M1) phase at a temperature of ≈68 °C. [ 11 − 13 ] To date, it has been established that external stimuli, such as light and electric fields, can effectively modulate the MIT behavior in VO 2 . [ 14 − 18 ] In particular, the electric field‐induced MIT (E‐MIT) of VO 2 has attracted attention due to its potential applications in memory and switching devices operating at room temperature.…”