Vanadium oxide is the chemical compound VO₂. It is formed in the contact process from V₂O₅, which acts as a catalyst.

Vanadium(IV) oxide is amphoteric, dissolving in non-oxidising acids to give the vanadyl ion

Vanadyl ion

The vanadyl or oxovanadium cation, [VO]2+, is a blue-coloured vanadium oxocation. It is one of the most stable diatomic ions known and forms a wide range of complexes.-Compounds containing the vanadyl ion:* vanadyl, VO2...

, [VO]²⁺ and in alkali to give the [V₄O₉]²⁻ ion, or at high pH [VO₄]⁴⁻.

Structure

At room temperature VO₂ has a distorted rutile

Titanium dioxide

Titanium dioxide, also known as titanium oxide or titania, is the naturally occurring oxide of titanium, chemical formula . When used as a pigment, it is called titanium white, Pigment White 6, or CI 77891. Generally it comes in two different forms, rutile and anatase. It has a wide range of...

 structure with shorter distances between pairs of V atoms indicating metal-metal bonding. Above 68°C the structure changes to an undistorted rutile structure and the metal-metal bonds are broken causing an increase in electrical conductivity and magnetic susceptibility as the bonding electrons are "released". The precise origin of this metal to insulator transition remains controversial, and is of particular interest in condensed matter physics

Condensed matter physics

Condensed matter physics deals with the physical properties of condensed phases of matter. These properties appear when a number of atoms at the supramolecular and macromolecular scale interact strongly and adhere to each other or are otherwise highly concentrated in a system. The most familiar...

.

Uses

Tungsten

Tungsten

Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...

-doped vanadium dioxide (W:VO₂) with 1.9% tungsten content has been investigated for use as a "spectrally-selective" window coating to block infrared

Infrared

Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

 transmission and reduce the loss of building interior heat through windows. This material behaves like a semiconductor

Semiconductor

A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...

 at temperatures below 29 °C, allowing more transmission, and like a conductor at higher temperatures, providing much greater reflectivity

Reflectivity

In optics and photometry, reflectivity is the fraction of incident radiation reflected by a surface. In general it must be treated as a directional property that is a function of the reflected direction, the incident direction, and the incident wavelength...

. Varying the amount of tungsten allows regulating the phase transition temperature. However, the coating has a slight yellow-green color.
Vanadium dioxide can act as an extremely fast optical shutter. The thermochromic phase transition

Phase transition

A phase transition is the transformation of a thermodynamic system from one phase or state of matter to another.A phase of a thermodynamic system and the states of matter have uniform physical properties....

 between the transparent semiconductive and reflective conductive phase, occurring at 68 °C, can happen in times as short as 100 femtoseconds.

Vanadium dioxide, especially in its nanocrystalline

Nanocrystalline

A nanocrystalline material is a polycrystalline material with a crystallite size of only a few nanometers. These materials fill the gap between amorphous materials without any longe range order and crystalline materials with a clear three dimensional long range order.X-ray diffraction is commonly...

 form, may find use in glazing applications, extremely fast optical shutters, optical modulator

Optical modulator

An optical modulator is a device which is used to modulate a beam of light. The beam may be carried over free space, or propagated through an optical waveguide. Depending on the parameter of a light beam which is manipulated, modulators may be categorized into amplitude modulators, phase...

s, infrared

Infrared

Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

 modulators for missile guidance

Missile guidance

Missile guidance refers to a variety of methods of guiding a missile or a guided bomb to its intended target. The missile's target accuracy is a critical factor for its effectiveness...

systems, cameras, data storage, and other applications.