Doubling of the Phase Transition Temperature of VO₂ by Fe Doping

Abstract

Vanadium dioxide (VO 2 ) undergoes a fully reversible first-order metal− insulator transition from the M1 monoclinic phase (P2 1 /c) to a high-temperature tetragonal phase (P4 2 /mnm) at around 68 °C. Modulation of the phase transition of VO 2 by chemical doping is of fundamental and technological interest. Here, we report the synthesis of highly crystallized Fe-doped VO 2 powders by a carbo-thermal reduction process. The impact of Fe doping on the structural and phase transition of VO 2 is studied. The as-prepared Fe-doped VO 2 samples crystallize in the M2 monoclinic form (C2/m), which is linked to segregation of the doping ions in the V2 zigzag chains. A large increase in the transition temperature to 134 °C is observed, which does correspond to a breakthrough in VO 2 -type thermochromic materials.

Element doping: a marvelous strategy for pioneering the smart applications of VO2

“…86,87 Fe is the most efficient element for increasing T MIT ; the highest transition temperature of 118 °C is reported in the available literature for VO 2 . 88 Actually, T MIT could be increased to 134 °C for the 12.6 at% doping sample, 2 times higher than the original value, but Fe 2 O 3 impurities are found. Rietveld refinement reveals that Fe has a strong influence on the structural phase transition of VO 2 .…”

Dispersed VO2 phases in a flexible sensor for recognizing tensile and compressive stress

“…In contrast to the M1 phase of VO 2 , the M2 phase transformed by internal and external stresses had higher resistivity and phase transition temperature. [45][46][47] It was documented that the conductivity and band gap were directly related to the gap between p* and bonding orbitals d II in VO 2 of insulator state. 48,49 Under a tensile stress, the bond length increased and affected the dimerization of V-V atoms, inducing an increased gap and attenuated conductance while under compressive stress, the shortened V-V chain pushed the formation of the R phase of VO 2 , 50 which resulted in a decreased resistance.…”

In Situ Three-Dimensional Electron Diffraction for Probing Structural Transformations of Single Nanocrystals

“…What differs from the previous reports is that, instead of 341 K, the phase transition temperature ( T c ) of VO 2 displayed from the temperature controller of the in situ heating holder here is approx . 373 K. The shift of T c is not uncommon in VO 2 . − For example, there are reports that doping with heterogeneous elements would incur a T c shift of VO 2 material, enabling a lower ( e.g ., W) or higher ( e.g ., Fe and Ge) phase transition temperature. Besides, according to Yoon, T c would vary as much as 26.1 K with the decrease of the microcrystal sizes of the VO 2 specimen.…”