Thermochromic characteristics of WO 3-doped vanadium dioxide thin films prepared by sol–gel method (original) (raw)
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Thin Solid Films, 2013
A simple and cost effective sol-gel process for producing vanadium dioxide thin films was developed via thermolysis of V 2 O 5 ·nH 2 O (n≈ 2) V V precursors prepared by dissolving vanadium powder or V 2 O 5 powder in 30% hydrogen peroxide solutions. After spin-coating on fused silica substrates and annealing at 750°C in vacuum, without any intermediate gas reducing step, the major phase VO 2 (M, monoclinic phase) was found in both of the films based on V-H 2 O 2 and V 2 O 5 -H 2 O 2 precursor, exhibiting large transmittance changes (>40%) in the IR region (>2000 nm) and small hysteresis loop width (b 5°C) which were comparable to reported epitaxial VO 2 films. The two films have similar metal-to-insulator transition temperature τ C =62.5°C, lower than the classical value of 68°C for VO 2 thin films. In addition, the method enables simple doping, as found for 0.56 at.% W-doped VO 2 films. This intrinsically simple solution process followed by one-step annealing makes it potentially useful in smart window applications.
The Effect of Alkali Metal (Na, K) Doping on Thermochromic Properties of VO 2 Films
This work reports the synthesis of undoped and alkali metal doped thermochromic vanadium dioxide thin films by sol-gel spin coating and subsequent low-temperature annealing at 450 °C in N 2-H 2 atmosphere. The effect of sodium and potassium on the phase transition temperature as well as on the solar modulations were investigated. A dopant concentration of 0.3 at% resulted in a reduction of the critical transition temperature (T c) from 62 °C to 57 °C and 47 °C for the sodium and potassium doped films, respectively. Moreover, both dopants improved the solar modulations (ΔT sol) of the undoped VO 2 films from 3.81 to 9.44 and 5.43 %, respectively.
Journal of Materials Chemistry, 2005
Atmospheric pressure chemical vapour deposition of V 22x M x O 2 (M = Mo, Nb; X = 0.01-0.003) thin films was achieved on glass substrates from the reaction of VOCl 3 , H 2 O and MCl 5 . Comparable reactions with SnCl 4 formed SnO 2 : VO 2 composites. The ease with which solid solutions or composite films formed was related to the relative reaction rates. The films were characterised by X-ray diffraction, Raman, X-ray photoelectron spectroscopy and scanning electron microscopy. Doping of the VO 2 phase was shown to affect both the growth morphology and the thermochromic properties of the films. The Mo-doped VO 2 films showed a thermochromic switch of 47 uC with a narrow hysteresis (4-6 uC).
Materials
Vanadium dioxide (VO2) with an insulator-to-metal (IMT) transition (∼68 °C) is considered a very attractive thermochromic material for smart window applications. Indeed, tailoring and understanding the thermochromic and surface properties at lower temperatures can enable room-temperature applications. The effect of W doping on the thermochromic, surface, and nanostructure properties of VO2 thin film was investigated in the present proof. W-doped VO2 thin films with different W contents were deposited by pulsed laser deposition (PLD) using V/W (+O2) and V2O5/W multilayers. Rapid thermal annealing at 400–450 °C under oxygen flow was performed to crystallize the as-deposited films. The thermochromic, surface chemistry, structural, and morphological properties of the thin films obtained were investigated. The results showed that the V5+ was more surface sensitive and W distribution was homogeneous in all samples. Moreover, the V2O5 acted as a W diffusion barrier during the annealing sta...
Thin Solid Films, 2004
This work deals with high efficient optical switching properties at 68 8C of thermochromic vanadium dioxide (VO) thin films 2 deposited on amorphous silica substrates. VO thin films were deposited by radio frequency reactive sputtering process. Conditions 2 of deposition were optimized making use of parameters such as film thickness, gas ratio and substrate temperature. Process was optimized adjusting the distance between target and substrate, and dimensions of target and substrates, to obtain a good uniformity and reproducibility of the layers. X-Ray diffraction patterns and scanning electron microscopy convincingly illustrated that VO 2 thin films could grow on amorphous silica substrates with a specific preferential crystal orientation: the w001x crystallographic M direction of oxygen octahedral chains is parallel to the substrate plane and corresponds with vanadium-vanadium links (insulating state) or with a maximum of electron delocalization (metal state). Optical switching properties in the mid-infrared range are discussed: transmittance, reflectance and emissivity values are strongly modified at the thermochromic transition temperature (Tcs68 8C). A maximum of optical transmittance contrast is observed for a thickness of 120-nm, then interpreted in terms of absorption law. Using a specific software, the n and k optical indices are determined and used to simulate the variation of transmittance vs. film thickness.
Surface and Coatings Technology, 2007
The atmospheric pressure chemical vapour deposition reaction of vanadyl acetylacetonate and tungsten hexachloride led to the production of thin films of tungsten doped monoclinic vanadium dioxide on glass substrates. Scanning electron microscopy indicated that the films had a columnar island growth morphology. Transmission and reflectance measurements elucidated a significant change in properties in the IR portion of the spectrum either side of the metal to semiconductor transition. Variable temperature transmission studies show that the metal to semiconductor transition was lowered by doping tungsten into the films and that this effect was dependent on the amount of tungsten doping.
Spray deposition of V4O9 and V2O5 thin films and post-annealing formation of thermochromic VO2
Journal of Alloys and Compounds, 2017
Vanadium oxide (VO x) thin films were deposited at various substrate temperatures (T s) by spray pyrolysis technique using 0.05 M vanadyl acetylacetonate precursor. V 4 O 9 films are formed at T s = 300ºC, while mixed V 2 O 5 phases are formed at higher T s (400 and 500ºC). Annealing in forming gas of V 4 O 9 films shows the formation of higher content of thermochromic VO 2 phase than V 2 O 5 films. V 4 O 9 films show little higher electric resistivity (ρ), higher temperature coefficient of resistance (TCR), and higher thermal carrier activation energy (E a) than V 2 O 5 films. Annealed VO x films show a 2-3 order of magnitude change in ρ, optical transmission switch of 19-39%, and higher E a than to the as deposited films. Annealed films deposited at T s =500ºC presents a high TCR of-4.6%K-1. Optical absorption, electronic transitions, and energy gaps of the formed VO x phases have been discussed in relation to its electronic band structure.
Influence of doping on the properties of vanadium oxide gel films
Journal of Physics: Condensed Matter, 2008
Effect of doping with H and W on the properties of V2O5 and VO2 derived from V2O5 gel has been studied. It is shown that the treatment of V2O5 in low-temperature RF hydrogen plasma for 1 to 10 min. leads to either hydration of vanadium pentoxide or its reduction (depending on the treatment conditions) to lower vanadium oxides. For some samples, which are subject to plasma treatment in the discharge active zone, a non-ordinary temperature dependence of resistance, with a maximum at T ~ 100 K, is observed. For W-doped VO2 films, it is shown that substitution of V 4+ with W 6+ results in a decrease of the temperature of metal-insulator transition. Also, it has been shown that the doping of the initial films with ~3 at.% of W reduces the statistical scatter in the threshold parameters of the switching devices with S-shaped I-V characteristics on the basis of V2O5 gel films.
Effects of Aluminium and Tungsten Co-Doping on the Optical Properties of VO2 Based Thin Films
Tanzania Journal of Science, 2018
Aluminium and tungsten co-doped vanadium dioxide (VO 2 :W:Al) thin films were deposited by DC reactive magnetron sputtering technique. In this work we report on the effects of aluminium and tungsten co–doping on the optical properties of vanadium dioxide (VO 2 ) based thin films with a view of combining both increased luminous transmittance (T lum ) and lowered transition temperature (τ c ). The effect of aluminium and tungsten co-doping on semiconductor-metal transition of vanadium dioxide films was investigated and compared with tungsten doped and undopedVO 2 films. Spectral transmittances of the films were obtained using Shimadzu SolidSpec-3700 DUV UV-VIS-NIR spectrophotometer. The results revealed that the transmittance of tungsten and aluminium co–doped vanadium dioxide using two Al pellets showed a peak at about 54% in the visible spectral range with fairly good switching characteristics and a transition temperature of 61 o C. Keywords : Transition temperature, luminous transm...