Vanadium(IV) oxide

Vanadium(IV) oxide
IUPAC name Vanadium(IV) oxide
Other names Vanadium dioxide Vanadium tetroxide
Identifiers
CAS number	12036-21-4 Y
PubChem	82849
Properties
Molecular formula	VO2
Molar mass	82.94 g/mol
Appearance	Deep Blue Powder [1]
Density	4.571 g/cm3 (monoclinic) 4.653 g/cm3 (tetragonal)
Melting point	1967 °C
Structure
Crystal structure	Distorted rutile (<70 ºC, monoclinic) Rutile (>70 ºC, tetragonal)
Hazards
EU Index	Not listed
R-phrases	36/37/38
S-phrases	26-36/37/39
NFPA 704	0 2 0
Flash point	Non-flammable
Related compounds
Other anions	Vanadium disulfide Vanadium diselenide Vanadium ditelluride
Other cations	Niobium(IV) oxide Tantalum(IV) oxide
Related vanadium oxides	Vanadium(II) oxide Vanadium(III) oxide Vanadium(V) oxide
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

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

Structure

At room temperature VO₂ has a distorted rutile structure with shorter distances between pairs of V atoms indicating metal-metal bonding. ^[2] 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".^[2] The precise origin of this metal to insulator transition remains controversial, and is of particular interest in condensed matter physics.

Uses

Tungsten-doped vanadium dioxide (W:VO₂) with 1.9% tungsten content has been investigated for use as a "spectrally-selective" window coating to block infrared transmission and reduce the loss of building interior heat through windows. This material behaves like a semiconductor at temperatures below 29 °C, allowing more transmission, and like a conductor at higher temperatures, providing much greater reflectivity.^[3][4] Varying the amount of tungsten allows regulating the phase transition temperature. However, the coating has a slight yellow-green color.^[5]

Nanostars of Vanadium(IV) oxide

Vanadium dioxide can act as an extremely fast optical shutter. The thermochromic phase transition between the transparent semiconductive and reflective conductive phase, occurring at 68 °C, can happen in times as short as 100 femtoseconds.^[6]

Vanadium dioxide, especially in its nanocrystalline form, may find use in glazing applications, extremely fast optical shutters, optical modulators, infrared modulators for missile guidance systems, cameras, data storage, and other applications.

See also

Vanadium redox battery

References

1. ^ Chemistry of the Elements 2nd Ed. - Greenwood p. 981
2. ^ ^{a b c} Greenwood, Norman N.; Earnshaw, A. (1984). Chemistry of the Elements. Oxford: Pergamon. pp. 1144–45. ISBN 0-08-022057-6. 
3. ^ Sol-Gel Vanadium oxide
4. ^ Intelligent Window Coatings that Allow Light In but Keep Heat Out - News Item
5. ^ oe magazine - Eye on Technology
6. ^ Timing nature’s fastest optical shutter