The properties of vanadium dioxide:

The molecular formula of vanadium dioxide is VO2, with a molecular weight of 82.94. It is a dark blue crystal powder with a monoclinic crystal structure. Insoluble in water, easily soluble in acid and alkali. When dissolved in acid, it cannot generate tetravalent ions, but generates positive divalent vanadium oxide ions. When heated to red heat in a dry hydrogen stream, it is reduced to vanadium trioxide, and can also be oxidized by air or nitric acid to produce vanadium pentoxide, which dissolves in alkali to form vanadate. It can be produced by reducing vanadium pentoxide with carbon, carbon monoxide, or oxalic acid. Used as a coloring agent for glass and ceramics.

Vanadium dioxide is a metal oxide with phase transition properties, with a phase transition temperature of 68 ℃. The structural changes before and after the phase transition result in a reversible transition of infrared light from transmission to reflection. Based on this characteristic, it has been applied in the field of intelligent temperature control thin films. Due to its excellent conductivity, it is also applied in electronic devices.

Vanadium oxide materials exhibit multiphase competition as insulators at relatively low temperatures. However, since the 1960s when research on vanadium dioxide began, this peculiar phase behavior has remained unknown to people. American scientists announced on November 23, 2010 that through systematic research on the phase transition of vanadium dioxide (from metal to insulator), they have uncovered a mystery that has plagued the academic community for decades. They found that the multiphase competition phenomenon of vanadium dioxide is purely caused by lattice symmetry, and believed that the vanadium dioxide lattice can undergo "folding" in different ways during cooling, so the phenomenon observed by people is the different folding forms of vanadium dioxide.

Several main applications of vanadium dioxide:

1. Wisdom Window

It is an optical device composed of a substrate (such as glass or other transparent materials) and a dimming substance. It can undergo coloring or fading reactions in certain sections of the solar spectrum under certain physical and chemical factors (such as light, electromagnetic radiation, electric field, gas, temperature), causing changes in the optical properties of the dimming substance. As a result, the spectrum selectively absorbs or reflects solar radiation, achieving the purpose of shielding ultraviolet rays, adjusting indoor sunlight intensity and indoor and outdoor heat exchange, reducing cooling and heating energy consumption, and reducing carbon emissions According to their different incentive methods, smart windows can be divided into three categories: thermally induced color change, gas induced color change, and electrically induced color change.

2. Terahertz metamaterials

The abrupt change in resistance before and after the phase transition of VO2 reaches the order of 104, and this change is reversible, making VO2 an excellent optoelectronic switch material. When the temperature is higher than the phase transition temperature, the resistance of VO2 is very small, almost like a conductor, which makes the circuit connected; When the temperature is below the phase transition temperature, the resistance of VO2 increases, causing the circuit to disconnect. This achieves intelligent control of temperature on the circuit. General VO2 thin film materials are suitable for working environments with lower currents, and the thermal hysteresis loop of the film material must be steep. However, block materials made of VO2 powder can withstand larger currents, making their application range more extensive.

3. Lithium battery cathode material

B-phase vanadium dioxide is mainly prepared by hydrothermal method, which has a high charge discharge specific capacity and great potential for application in lithium ion pool cathode materials. Synthesis of hydrated vanadium pentoxide nanoribbons modified with reduced oxidized alkenes via hydrothermal method. Then annealed at 300 ℃ in nitrogen to obtain the cathode electrode of the lithium battery. This VO2./RGO thin film grid structure provides an efficient conduction pathway for electrons, while also reducing the diffusion distance of lithium ions. Electrochemical tests have shown that the cathode membrane can provide high reversible specific capacity and good cycling stability.

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