Vanadium(IV) oxide

Vanadium(IV) oxide

Names
IUPAC name Vanadium(IV) oxide
Other names Vanadium dioxide Vanadium tetroxide
Identifiers
CAS Number	12036-21-4
ECHA InfoCard	100.031.661
PubChem	82849
Properties
Chemical formula	VO2
Molar mass	82.94 g/mol
Appearance	Deep Blue Powder
Density	4.571 g/cm^3 (monoclinic) 4.653 g/cm^3 (tetragonal)
Melting point	1,967 °C
Structure
Crystal structure	Distorted rutile (<70 °C, monoclinic) Rutile (>70 °C, tetragonal)
Hazards
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
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Vanadium(IV) dioxide is an inorganic compound with the formula VO₂. It is a dark blue solid. Vanadium(IV) dioxide is amphoteric, dissolving in non-oxidising acids to give the blue vanadyl ion, [VO]²⁺ and in alkali to give the brown [V₄O₉]²⁻ ion, or at high pH [VO₄]⁴⁻.^[1] VO₂ has a phase transition very close to room temperature(~66 °C). Electrical resistivity, opacity, etc, can change up several orders. Due to these properties, it has been widely used in surface coating,^[2] sensors,^[3] and imaging.^[4] Potential applications include use in memory devices.^[5]

Properties

Structure

At temperatures below T_c=340 K, VO
2 has a monoclinic (space group P2₁/c) crystal structure. Above T_c, the structure is tetragonal, like rutile TiO
2. In the monoclinic phase, the V⁴⁺ ions form pairs along the c axis, leading to alternate short and long V-V distances of 2.65 Å and 3.12 Å. In comparison, in the rutile phase the V⁴⁺ ions are separated by a fixed distance of 2.96 Å. As a result, the number of V⁴⁺ ions in the crystallographic unit cell doubles from the rutile to the monoclinic phase.^[6]

The equilibrium morphology of rutile VO
2 particles is acicular, laterally confined by (110) surfaces, which are the most stable termination planes.^[7] The surface tends to be oxidized with respect to the stoichiometric composition, with the oxygen adsorbed on the (110) surface forming vanadyl species.^[7] The presence of V⁵⁺ ions at the surface of VO
2 films has been observed by x-ray photoelectron spectroscopy (XPS) measurements.^[8]

Electronic

At the rutile to monoclinic transition temperature, VO
2 also exhibits a metal to semiconductor transition in its electronic structure: the rutile phase is metallic while the monoclinic phase is semiconducting.^[9] The optical band gap of VO₂ in the low-temperature monoclinic phase is about 0.7 eV.^[10]

Synthesis and structure

Following the method described by Berzelius, VO
2 is prepared by comproportionation of vanadium(III) oxide and vanadium(V) oxide:^[11]

V
2O
5 + V
2O
3 → 4 VO
2

At room temperature VO₂ has a distorted rutile 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".^[1][12] The origin of this insulator to metal transition remains controversial and is of interest in condensed matter physics.

Infrared reflectance

VO
2 expresses temperature-dependent reflective properties. When heated from room temperature to 80 °C, the material's thermal radiation rises normally until 74 °C, before suddenly appearing to drop around 20 °C. At room temperature VO
2 is almost transparent to infrared light. As its temperature rises it gradually changes to reflective. At intermediate temperatures it behaves as a highly absorbing dielectric.^[13][14]

A thin film of vanadium oxide on a highly reflecting substrate (for specific infrared wavelengths) such as sapphire is either absorbing or reflecting, dependent on temperature. Its emissivity varies considerably with temperature. When the vanadium oxide transitions with increased temperature, the structure undergoes a sudden decrease in emissivity – looking colder to infrared cameras than it really is.^[13]

Varying the substrate materials e.g., to indium tin oxide, and modifying the vanadium oxide coating using doping, straining and other processes, alter the wavelengths and temperature ranges at which the thermal effects are observed.^[13]

Nanoscale structures that appear naturally in the materials' transition region can suppress thermal radiation as the temperature rises. Doping the coating with tungsten lowers the effect's thermal range to room temperature.^[13]

Uses

Infrared radiation management

1.9% tungsten-doped material 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.^[15][16] Varying the amount of tungsten allows regulating the phase transition temperature. The coating has a slight yellow-green color.^[17]

Other potential applications of its thermal properties include passive camouflage, thermal beacons, communication or to deliberately speed up or slow down cooling – which could be useful in a variety of structures from homes to satellites.^[13]

Nanostars of Vanadium(IV) oxide

Vanadium dioxide can act as extremely fast optical shutters, optical modulators, infrared modulators for missile guidance systems, cameras, data storage, and other applications. 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.^[18]

Phase change computing and memory

The insulator-metal phase transition in VO₂ can be manipulated at the nanoscale using a biased conducting atomic force microscope tip,^[19] suggesting applications in computing and information storage.^[20]

See also

• Vanadium redox battery

References

1. Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements. Oxford: Pergamon Press. pp. 1144–45. ISBN 0-08-022057-6.
2. Li, Yamei; Ji, Shidong; Gao, Yanfeng; Luo, Hongjie; Kanehira, Minoru (2013-04-02). "Core-shell VO2@TiO2 nanorods that combine thermochromic and photocatalytic properties for application as energy-saving smart coatings". Scientific Reports. 3. doi:10.1038/srep01370. PMC 3613806. PMID 23546301.
3. Hu, Bin; Ding, Yong; Chen, Wen; Kulkarni, Dhaval; Shen, Yue; Tsukruk, Vladimir V.; Wang, Zhong Lin (2010-12-01). "External-Strain Induced Insulating Phase Transition in VO2 Nanobeam and Its Application as Flexible Strain Sensor". Advanced Materials. 22 (45): 5134–5139. doi:10.1002/adma.201002868. ISSN 1521-4095.
4. Gurvitch, M.; Luryi, S.; Polyakov, A.; Shabalov, A. (2009-11-15). "Nonhysteretic behavior inside the hysteresis loop of VO2 and its possible application in infrared imaging". Journal of Applied Physics. 106 (10): 104504. doi:10.1063/1.3243286. ISSN 0021-8979.
5. Xie, Rongguo; Bui, Cong Tinh; Varghese, Binni; Zhang, Qingxin; Sow, Chorng Haur; Li, Baowen; Thong, John T. L. (2011-05-10). "An Electrically Tuned Solid-State Thermal Memory Based on Metal–Insulator Transition of Single-Crystalline VO2 Nanobeams". Advanced Functional Materials. 21 (9): 1602–1607. doi:10.1002/adfm.201002436. ISSN 1616-3028.
6. Morin, F. J. (1959). "Oxides Which Show a Metal-to-Insulator Transition at the Neel Temperature". Physical Review Letters. 3 (1): 34–36. doi:10.1103/PhysRevLett.3.34. ISSN 0031-9007.
7. Mellan, Thomas A.; Grau-Crespo, Ricardo (2012). "Density functional theory study of rutile VO₂ surfaces". The Journal of Chemical Physics. 137 (15): 154706. doi:10.1063/1.4758319. ISSN 0021-9606.
8. Manning, Troy D.; Parkin, Ivan P.; Pemble, Martyn E.; Sheel, David; Vernardou, Dimitra (2004). "Intelligent Window Coatings: Atmospheric Pressure Chemical Vapor Deposition of Tungsten-Doped Vanadium Dioxide". Chemistry of Materials. 16 (4): 744–749. doi:10.1021/cm034905y. ISSN 0897-4756.
9. Goodenough, John B. (1971-11-01). "The two components of the crystallographic transition in VO2". Journal of Solid State Chemistry. 3 (4): 490–500. doi:10.1016/0022-4596(71)90091-0.
10. Shin, S.; Suga, S.; Taniguchi, M.; Fujisawa, M.; Kanzaki, H.; Fujimori, A.; Daimon, H.; Ueda, Y.; Kosuge, K. "Vacuum-ultraviolet reflectance and photoemission study of the metal-insulator phase transitions in VO 2 , V 6 O 13 , and V 2 O 3". Physical Review B. 41 (8): 4993–5009. doi:10.1103/physrevb.41.4993.
11. Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 1267.
12. http://phys.org/news/2015-04-insulator-to-metal-transition-vanadium-dioxide.html
13. "Natural metamaterial looks cooler when heated". physicsworld.com. Retrieved 2014-01-01.
14. Kats, M. A.; Blanchard, R.; Zhang, S.; Genevet, P.; Ko, C.; Ramanathan, S.; Capasso, F. (2013). "Vanadium Dioxide as a Natural Disordered Metamaterial: Perfect Thermal Emission and Large Broadband Negative Differential Thermal Emittance". Physical Review X. 3 (4). doi:10.1103/PhysRevX.3.041004.
15. "Sol-Gel Vanadium oxide". Solgel.com. Retrieved 2012-09-12.
16. "Intelligent Window Coatings that Allow Light In but Keep Heat Out - News Item". Azom.com. Retrieved 2012-09-12.
17. "Eye on Technology". oe magazine. 2009-11-03. Retrieved 2012-09-12.
18. "Timing nature's fastest optical shutter". Physorg.com. Retrieved 2012-09-12.
19. Jeehoon Kim; Ko, Changhyun; Frenzel, Alex; Ramanathan, Shriram; Hoffman, Jennifer E. (2010). "Nanoscale imaging and control of resistance switching in VO₂ at room temperature". Applied Physics Letters. 96: 213106. doi:10.1063/1.3435466.
20. Zhou, You; Ramanathan, S. (2015-08-01). "Mott Memory and Neuromorphic Devices". Proceedings of the IEEE. 103 (8): 1289–1310. doi:10.1109/JPROC.2015.2431914. ISSN 0018-9219.