Two-Step Synthesis of VO₂ (M) with Tuned Crystallinity

Abstract

Highly crystallized monoclinic vanadium dioxide, VO (M), is successfully synthesized by a two-step thermal treatment: thermolysis of vanadyl ethylene glycolate (VEG) and postannealing of the poorly crystallized VO powder. In the first thermolysis step, the decomposition of VEG at 300 °C is investigated by X-ray diffraction and scanning electron microscopy (SEM). A poorly crystallized VO powder is obtained at a strict time of 3 min, and it is found that the residual carbon content in the powder played a critical role in the post crystallization of VO (M). After postannealing at 500 and 700 °C in an oxygen-free atmosphere, VO particles of various morphologies, of which the crystallite size increases with increasing temperature, are observed by SEM and transmission electron microscopy. The weight percent of crystalline VO, calculated using the Fullprof program, increases from 44% to 79% and 100% after postannealing. The improved crystallinity leads to an improvement in metal-insulator transition behaviors demonstrated by sharper and more intense differential scanning calorimetry peaks. Moreover, VO and VO with novel and particular microstructures are also successfully prepared with a similar two-step method using postannealing treatment under reductive or oxidizing atmospheres, respectively.

Synthesis of Tungsten-Doped Vanadium Dioxide Using a Modified Polyol Method Involving 1-Dodecanol

“…The appearance of the oxidized V 6 O 13 peaks originates from the increase in oxygen contents in W-VEG as the molar ratio of 1-dodecanol increases. It appears that excess oxygen atoms incorporated into the VO 2 structure chemically interact with vanadium atoms to form a new oxidation state of V 6 O 13 , as stated in literature [23].…”

Carbon-reduction as an easy route for the synthesis of VO2 (M1) and further Al, Ti doping

“…According to our previous study, [26] V2O3 powder can be obtained by annealing the VEG precursor directly in inert atmospheres or vacuum environment. V2O3 is synthesized when the VEG is annealed at 500°C for 5 h in sealed vacuum system, which is due to the reducibility of carbon from the VEG (VC2H4O3).…”

“…The process has already been described in details in our previous work. [26] After being heated at 300°C for 90 minutes in air, nano V2O5 is prepared. Then various molar ratios of soot are mixed with the as-synthesized V2O5 (i.e.…”

“…Interestingly, it was found that the carbon acts as a reducing agent on the formation of VO2 (M1). [26] Inspired by these observations, herein soot (carbon) is chosen for a direct reduction of nano V2O5. The comparison of dynamic and sealed vacuum systems associated with an accurate control of the carbon contents allows further understanding of the reductive mechanism.…”

One-step hydrothermal synthesis and thermochromic properties of chlorine-doped VO2(M) for smart window application

“…The use of a physical process such as magneton sputtering, 19 pulsed laser deposition, 20 crystal vapor deposition, 12,21 high power impulse magnetron sputtering (HIPMIS), 22 colloidal lithography, 23 chemical solution deposition 24 can result in thin film with desirable quantity. The chemical methods such as sol-gel method, chemical vapor deposition, polymer-assisted deposition [25][26][27][28] solvothermal and hydrothermal method [29][30][31] have been widely known to give the result of high-quality nanoscale VO 2 (M) with the easiness of phase and morphology control. The hydrothermal reaction is a cost-effective and facile reaction for the synthesis of VO 2 (M) nanoparticle with lower critical temperature.…”