Tungsten-doped Vanadium Dioxide Film Preparation

Vanadium dioxide (V0₂) is a typical temperature-controlled phase change material, which undergoes a reversible metal semiconductor phase transition from low temperature monoclinic phase (M phase) to high temperature rutile phase (R phase) at 68 ℃. However, in practical application, 68 is obviously not the appropriate temperature for human beings. Therefore, in order to make vanadium dioxide play a role, it is necessary to reduce the phase transition temperature of vanadium dioxide from 68 to the room temperature (25 ℃), in order to maximize the energy-saving efficiency of vanadium dioxide.

Among the various doped vanadium dioxides, the most effective and commonly used one is doped tungsten vanadium dioxide. Doping tungsten can significantly reduce the phase transition temperature of VO₂. By mole percentage, each phase of tungsten doped can reduce the phase transition temperature of vanadium dioxide by 28 ℃. However, doping tungsten vanadium dioxide also has some problems: for example, (1) the ability to reduce the phase transition temperature of vanadium dioxide by doping tungsten is unstable, and the results of different preparation systems are very different, metal tungsten or tungsten. Alkoxides are used as raw materials. These raw materials are not only expensive but also extremely unstable. The storage conditions are demanding. In short, this process is not a simple one, and the process of tungsten-doped vanadium dioxide film is first needed. An acid tungsten sol was prepared.

In the 25ml deionized water, 0.051g ammonium tungstate is added, and ammonium tungstate is not dissolved to form suspension. The suspension was heated to 20 ℃, then 0.5 mol/L hydrochloric acid was added drop by drop until the solution pH was 3.0, at which time all ammonium tungstate was dissolved. After natural cooling, the solution was fixed in a 50 ml capacity bottle with deionized water, and the cooled object was measured. The obvious Bundar effect was observed, i.e. the acidic tungsten sol with tungsten concentration of 0.004 mol/L was obtained.

Vanadium dichloride 50 ml deionized water and 3.8 g PVP were added into 250 ml beaker and stirred until blue transparent solution was obtained, in which the concentration of vanadium ion was 0.5 mol/L. According to the molar ratio of tungsten ion to vanadium ion is 0.05:1, acid tungsten doping agent is added to the above blue transparent solution, and a stable coating solution is obtained after stirring for one hour.

Quartz glass is cleaned by standard RCA to remove contaminated organic matter, dust and metal ion impurities on the surface of glass. Spin coating is used for coating for 10 minutes. Vanadium dioxide film can be obtained by holding at 500 ℃ for 0.5 hours in nitrogen atmosphere and then naturally decreasing the furnace temperature. The film thickness is 78 nm.

The preparation of acidic tungsten sol can provide stable tungsten source under acidic conditions. It can be widely used as tungsten source for vanadium trioxide and doped tungsten vanadium dioxide products. It is widely used in energy-saving films, energy-saving coatings, solar energy temperature control devices or energy information equipment. For example, micro photoelectric switching devices, thermistors, battery materials and optical information memory devices are easy to control, low cost and suitable for large-scale production.

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