Editing Tungsten trioxide

{{chembox
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 440453423
| Name = Tungsten trioxide
| ImageFile = Tungsten trioxide.png
| ImageName = Sample of Tungsten(VI) Oxide
| ImageSize = 270 px
| ImageFile1 = Kristallstruktur Wolfram(VI)-oxid.png
| IUPACName = Tungsten trioxide
| OtherNames = Tungstic anhydride<br />Tungsten(VI) oxide<br />Tungstic oxide
|Section1={{Chembox Identifiers
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo = 1314-35-8
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 940E10M08M
| RTECS = YO7760000
| PubChem = 14811
| InChI = 1S/3O.W
| SMILES = O=[W](=O)=O
}}
|Section2={{Chembox Properties
| Formula = WO<sub>3</sub>
| MolarMass = 231.84 g/mol
| Appearance = Canary yellow powder
| Density = 7.16 g/cm<sup>3</sup>
| Solubility = insoluble
| SolubleOther = slightly soluble in [[hydrofluoric acid|HF]]
| MeltingPtC = 1473
| BoilingPtC = 1700
| BoilingPt_notes = approximation
| MagSus = −15.8·10<sup>−6</sup> cm<sup>3</sup>/mol
}}
|Section3={{Chembox Structure
| Coordination = Octahedral (W<sup>VI</sup>)<br />Trigonal planar (O<sup>2– </sup>)
| CrystalStruct = [[Monoclinic]], [[Pearson symbol|mP32]]
| SpaceGroup = P12<sub>1</sub>/n1, No. 14
}}
|Section7={{Chembox Hazards
| ExternalSDS = [http://avogadro.chem.iastate.edu/MSDS/WO3.htm External MSDS]
| HPhrases = 
| PPhrases = 
| GHS_ref  = 
| MainHazards = Irritant
| NFPA-H = 
| NFPA-F = 
| NFPA-R = 
| NFPA-S = 
| FlashPt = Non-flammable
}}
|Section8={{Chembox Related
| OtherAnions = [[Tungsten trisulfide]]
| OtherCations = [[Chromium trioxide]]<br />[[Molybdenum trioxide]]
| OtherFunction = [[Tungsten(III) oxide]]<br />[[Tungsten(IV) oxide]]
| OtherFunction_label = [[tungsten]] [[oxide]]s
| OtherCompounds = 
}}
}}

'''Tungsten(VI) oxide''', also known as '''tungsten trioxide''' is a chemical compound of [[oxygen]] and the transition metal [[tungsten]], with [[chemical formula|formula]] WO<sub>3</sub>.  The compound is also called '''tungstic anhydride''', reflecting its relation to [[tungstic acid]] {{chem2|H2WO4}}.  It is a light yellow crystalline solid.<ref name=chri2011/>

Tungsten(VI) oxide occurs naturally in the form of [[hydrate]]s, which include minerals: [[tungstite]] WO<sub>3</sub>·H<sub>2</sub>O, [[meymacite]] WO<sub>3</sub>·2H<sub>2</sub>O and [[hydrotungstite]] (of the same composition as meymacite, however sometimes written as H<sub>2</sub>WO<sub>4</sub>). These minerals are rare to very rare secondary tungsten minerals.

==History==
In 1841, a chemist named Robert Oxland gave the first procedures for preparing tungsten trioxide and [[sodium tungstate]].<ref name=lass1999/> He was granted patents for his work soon after, and is considered to be the founder of systematic tungsten chemistry.<ref name=lass1999/>

==Structure and properties==
The crystal structure of tungsten trioxide is temperature dependent. It is [[tetragonal]] at temperatures above 740&nbsp;°C, [[orthorhombic]] from 330 to 740&nbsp;°C, [[monoclinic]] from 17 to 330&nbsp;°C, [[triclinic]] from −50 to 17&nbsp;°C, and monoclinic again at temperatures below −50&nbsp;°C.<ref name=wrie1989/> The most common structure of WO<sub>3</sub> is monoclinic with [[space group]] P2<sub>1</sub>/n.<ref name=lass1999/>

The pure compound is an electric insulator, but oxygen-deficient varieties, such as {{chem2|WO_{2.90}|}} = {{chem2|W20O58}}, are dark blue to purple in color and conduct electricity.  They can be prepared by combining the trioxide and the [[tungsten dioxide|dioxide]] {{chem2|WO2}} at 1000&nbsp;°C in vacuum.<ref name=shen2020/><ref name=chri2011/>

Possible signs of [[superconductivity]] with critical temperatures T<sub>c</sub> = 80–90&nbsp;K were claimed in sodium-doped and oxygen-deficient WO<sub>3</sub> crystals. If confirmed, these would be the first superconducting materials containing no copper, with T<sub>c</sub> higher than the boiling point of liquid nitrogen at normal pressure.<ref name=reic1999/><ref name=shen2020/>

=== Crystallography ===

Tungsten trioxide exists in multiple polymorphs whose structures have been precisely determined using [[X-ray crystallography]] and [[neutron diffraction]]. Each phase exhibits a distinct arrangement of distorted WO<sub>6</sub> octahedra, which affect its electronic and optical behavior.

Tungsten trioxide (WO₃) is a polymorphic compound whose crystal structure changes depending on temperature. It adopts several forms, including:

* [[Tetragonal]] above 740 °C  
* [[Orthorhombic]] from 330 to 740 °C  
* [[Monoclinic]] from 17 to 330 °C  
* [[Triclinic]] from −50 to 17 °C  
* A second monoclinic phase below −50 °C  
* A [[Hexagonal crystal family|Hexagonal]] form synthesized under specific conditions

The most common ambient phase is monoclinic with space group ''P2₁/n'', featuring distorted WO₆ octahedra linked at their corners. Each polymorph exhibits variations in symmetry, lattice parameters, and atomic positions, making structural determination important for understanding the material’s physical and electronic properties.

==== Tetragonal WO₃ ====
This high-temperature phase is observed above 740 °C, but specific crystallographic data are often not tabulated separately in modern studies. It exhibits relatively symmetric WO₆ octahedra.

==== Orthorhombic WO₃ ====
* '''Space group:''' ''Pmnb'' (No. 62)  
* '''Lattice parameters (Å):''' a = 7.341(4), b = 7.570(4), c = 7.754(4)  
* '''Angles (°):''' α = β = γ = 90°  
* '''Cell volume:''' 430.90 Å³  
* '''Z:''' 8  
* '''Temperature:''' 873 K  
* '''Pressure:''' Atmospheric  
* '''R-value:''' 0.061  
* '''Reference:''' Salje, E. (1977). ''Acta Crystallographica Section B'', 33(2), 574–577.<ref name="Sundberg 2144–2149">{{Cite journal |last=Sundberg |first=M. |date=1976-07-15 |title=The crystal and defect structures of W25O73, a member of the homologous series WnO3n−2 |url=https://journals.iucr.org/paper?S0567740876007280 |journal=Acta Crystallographica Section B: Structural Crystallography and Crystal Chemistry |language=en |volume=32 |issue=7 |pages=2144–2149 |doi=10.1107/S0567740876007280 |issn=0567-7408|url-access=subscription }}</ref>

==== Monoclinic WO₃ ====
* '''Space group:''' ''P1/c1'' (No. 7)  
* '''Lattice parameters (Å):''' a = 5.27710(1), b = 5.15541(1), c = 7.66297(1)  
* '''Angles (°):''' α = γ = 90°, β = 91.7590(2)  
* '''Cell volume:''' 208.38 Å³  
* '''Z:''' 4  
* '''Temperature:''' 5 K  
* '''Pressure:''' Atmospheric  
* '''R-value:''' 0.09  
* '''Reference:''' Salje, E.K.H. et al. (1997). ''Journal of Physics: Condensed Matter'', 9, 6563–6577.<ref name="Sundberg 2144–2149"/>
[[File:WO3 triclinic structure.png|thumb|WO3 triclinic structure]]

==== Triclinic WO₃ ====
* '''Space group:''' ''P−1'' (No. 2)  
* '''Lattice parameters (Å):''' a = 7.309(2), b = 7.522(2), c = 7.678(2)  
* '''Angles (°):''' α = 88.81(2), β = 90.92(2), γ = 90.93(2)  
* '''Cell volume:''' 421.92 Å³  
* '''Z:''' 8  
* '''Temperature:''' Room temperature  
* '''Pressure:''' Atmospheric  
* '''R-value:''' 0.05  
* '''Reference:''' Diehl, R. et al. (1978). ''Acta Crystallographica Section B'', 34, 1105–1111.<ref name="Sundberg 2144–2149"/>

==== Hexagonal WO₃ ====
A less common hexagonal polymorph of WO₃ has been reported and characterized using powder X-ray diffraction. It exhibits higher symmetry and potentially distinct electronic properties.

* '''Space group:''' ''P6/mmm'' (No. 191)  
* '''Lattice parameters (Å):''' a = 7.298(2), c = 3.899(2)  
* '''Angles (°):''' α = β = 90°, γ = 120°  
* '''Cell volume:''' 179.84 Å³  
* '''Z:''' 3  
* '''Temperature:''' Room temperature  
* '''Pressure:''' Atmospheric  
* '''R-value:''' 0.055  
* '''Reference:''' Gérand, B. et al. (1979). ''Journal of Solid State Chemistry'', 29, 429–434.<ref name="Sundberg 2144–2149"/>

==Preparation==
===Industrial===
Tungsten trioxide is obtained as an intermediate in the recovery of tungsten from its minerals.<ref name=prad2003/> Tungsten ores can be treated with [[alkali]]s to produce soluble [[tungstate]]s. Alternatively, CaWO<sub>4</sub>, or [[scheelite]], is allowed to react with [[HCl]] to produce [[tungstic acid]], which decomposes to WO<sub>3</sub> and water at high temperatures.<ref name=prad2003/>

:CaWO<sub>4</sub> + 2 HCl → CaCl<sub>2</sub> + H<sub>2</sub>WO<sub>4</sub>
:H<sub>2</sub>WO<sub>4</sub> → {{H2O}} + WO<sub>3</sub>

===Laboratory===
Another common way to synthesize WO<sub>3</sub> is by [[calcination]] of [[ammonium paratungstate]] (APT) under oxidizing conditions:<ref name=lass1999/>

:(NH<sub>4</sub>)<sub>10</sub>[H<sub>2</sub>W<sub>12</sub>O<sub>42</sub>]{{Hydrate|4}} → 12 WO<sub>3</sub> + 10 NH<sub>3</sub> + 10 {{H2O}}

==Reactions==
Tungsten trioxide can be reduced with [[carbon]] or [[hydrogen]] gas yielding the pure metal.{{Citation needed|reason=Primary reference for these reactions should be provided|date=November 2015}}

:2 WO<sub>3</sub> + 3 C → 2 W + 3 CO<sub>2</sub>  (high temperature)
:WO<sub>3</sub> + 3 H<sub>2</sub> → W + 3 H<sub>2</sub>O  (550–850&nbsp;°C)

==Uses==
Tungsten trioxide is a starting material for the synthesis of [[tungstate]]s.  [[Barium tungstate]] {{chem2|BaWO4}} is used as a [[x-ray]] screen [[phosphor]]s. Alkali metal tungstates, such as [[lithium tungstate]] {{chem2|Li2WO4}} and [[cesium tungstate]] {{chem2|Cs2WO4}}, give dense solutions that can be used to separate minerals.<ref name=chri2011/> Other applications, actual or potential, include:

* [[Fireproofing]] fabrics<ref name=merck2006/>
* [[gas sensor|Gas]] and [[hygrometer|humidity sensor]]s.<ref name=will2002/><ref name=chri2011/>
* [[Ceramic glaze]]s where it gives a rich yellow color.<ref name=prad2003/><ref name=chri2011/>
* [[Electrochromic]] glass, such as in [[smart windows]], whose transparency can be changed by an applied voltage.<ref name=leew2000/><ref name=pate2013/><ref name=chri2011/>
* [[Photocatalytic water splitting]].<ref name=mise2010/><ref name=kara2013/><ref name=szek2016/><ref name=baia2016/>
* Substrate for [[surface-enhanced Raman spectroscopy]] replacing noble metals.<ref name=oug2018/><ref name=hurst2011/><ref name=liuw2018/><ref name=zhou2019/>

==References==

<references>

<ref name=pate2013>K. J. Patel, M. S. Desai, C. J. Panchal, H. N. Deota, and U. B. Trivedi (2013): "[https://essuir.sumdu.edu.ua/handle/123456789/31017 All-Solid-Thin Film Electrochromic Devices Consisting of Layers ITO / NiO / ZrO2 / WO3 / ITO]". ''Journal of Nano-Electronics and Physics'', volume 5, issue 2, article 02023.</ref>

<ref name=reic1999>S. Reich and Y. Tsabba (1999): "Possible nucleation of a 2D superconducting phase on WO single crystals surface doped with Na". ''European Physical Journal B'', volume 9, pages = 1–4. {{doi|10.1007/s100510050735}} {{s2cid|121476634}}</ref>

<ref name=shen2020>A. Shengelaya, K. Conder, and K. A. Müller (2020): "Signatures of Filamentary Superconductivity up to 94 K in Tungsten Oxide WO<sub>2.90</sub>". ''Journal of Superconductivity and Novel Magnetism'', volume 33, pages 301–306. {{doi|10.1007/s10948-019-05329-9}}</ref>

<ref name=will2002>David E Williams, Simon R Aliwell, Keith F. E. Pratt, Daren J. Caruana, Roderic L. Jones, R. Anthony Cox, Graeme M. Hansford. and John Halsall (2002): "Modelling the response of a tungsten oxide semiconductor as a gas sensor for the measurement of ozone".  ''Measurement Science and Technology''. volume 13. pages 923–931. {{doi|10.1088/0957-0233/13/6/314}}</ref>

<ref name=mise2010>Yugo Miseki, Hitoshi Kusama, Hideki Sugihara, and Kazuhiro Sayama (2010): "Cs-Modified WO3 Photocatalyst Showing Efficient Solar Energy Conversion for O2 Production and Fe (III) Ion Reduction under Visible Light". ''Journal of Physical Chemistry Letters'', volume 1, issue 8, pages 1196–1200. {{doi|10.1021/jz100233w}}</ref>

<ref name=kara2013>É. Karácsonyi, L. Baia, A. Dombi, V. Danciu, K. Mogyorósi, L. C. Pop, G. Kovács, V. Coşoveanu, A. Vulpoi, S. Simon, Zs. Pap (2013): "The photocatalytic activity of TiO2/WO3/noble metal (Au or Pt) nanoarchitectures obtained by selective photodeposition". ''Catalysis Today'', volume 208, pages 19-27. {{doi|10.1016/j.cattod.2012.09.038}}</ref>

<ref name=szek2016>István Székely, Gábor Kovács, Lucian Baia, Virginia Danciu, Zsolt Pap (2016): "Synthesis of Shape-Tailored WO3 Micro-/Nanocrystals and the Photocatalytic Activity of WO3/TiO2 Composites". ''Materials'', volume 9, issue 4, pages 258-271. {{doi|10.3390/ma9040258|doi-access=free}}</ref>

<ref name=baia2016>Lucian Baia, Eszter Orbán, Szilvia Fodor, Boglárka Hampel, Endre Zsolt Kedves, Kata Saszet, István Székely, Éva Karácsonyi, Balázs Réti, Péter Berki, Adriana Vulpoi, Klára Magyari, Alexandra Csavdári, Csaba Bolla, Veronica Coșoveanu, Klára Hernádi, Monica Baia, András Dombi, Virginia Danciu, Gábor Kovácz, Zsolt Pap (2016): "Preparation of TiO2/WO3 composite photocatalysts by the adjustment of the semiconductors' surface charge". ''Materials Science in Semiconductor Processing'', volume 42, part 1, pages 66-71. {{doi|10.1016/j.mssp.2015.08.042}}</ref>

<ref name=oug2018>{{cite journal|author=G. Ou|title=Tuning Defects in Oxides at Room Temperature by Lithium Reduction |journal=Nature Communications|volume=9|date=2018|doi=10.1038/s41467-018-03765-0|issue=1302|pages=1302 |pmid=29615620 |pmc=5882908 |bibcode=2018NatCo...9.1302O }}</ref>

<ref name=hurst2011>{{cite journal|author=S. Hurst|title=Utilizing Chemical Raman Enhancement: A Route for Metal Oxide Support Based Biodetection |journal=The Journal of Physical Chemistry C |volume=115|pages=620–630|date=2011|doi=10.1021/jp1096162|issue=3}}</ref>

<ref name=liuw2018>{{cite journal|author=W. Liu|title= Improved Surface-Enhanced Raman Spectroscopy Sensitivity on Metallic Tungsten Oxide by the Synergistic Effect of Surface Plasmon Resonance Coupling and Charge Transfer |journal=The Journal of Physical Chemistry Letters|volume=9 |pages=4096–4100|date=2018|doi=10.1021/acs.jpclett.8b01624|issue=14|pmid= 29979872 |s2cid= 49716355 |url=https://www.nature.com/articles/s41467-018-03765-0|url-access=subscription}}</ref>

<ref name=zhou2019>{{cite journal|author=C. Zhou|title=Electrical tuning of the SERS enhancement by precise defect density control |journal=ACS Applied Materials & Interfaces|volume=11|pages=34091–34099|date=2019|doi=10.1021/acsami.9b10856|issue=37 |pmid=31433618 |s2cid=201278374 |url=http://www.unilim.fr/pages_perso/zeng/a196.pdf }}</ref>

<ref name=prad2003>{{cite book|last =Patnaik|first =Pradyot|year = 2003|title =Handbook of Inorganic Chemical Compounds|publisher = McGraw-Hill|isbn =978-0-07-049439-8|url= https://books.google.com/books?id=Xqj-TTzkvTEC|access-date = 2009-06-06}}</ref>

<ref name=lass1999>{{cite book|author=Lassner, Erik and Wolf-Dieter Schubert|title= Tungsten: Properties, Chemistry, Technology of the Element, Alloys, and Chemical Compounds|place=New York|publisher=Kluwer Academic|year=1999|isbn=978-0-306-45053-2}}</ref>

<ref name=wrie1989>H. A. Wriedt (1898): "The O-W (oxygen-tungsten) system".  ''Bulletin of Alloy Phase Diagrams.'', volume 10, pages 368–384. {{doi|10.1007/BF02877593}}</ref>

<ref name=merck2006>Merck (2006): "Tungsten trioxide." ''The Merck Index'', volume 14.</ref>

<ref name=chri2011>J. Christian, R.P. Singh Gaur, T. Wolfe and J. R. L. Trasorras (2011): ''[https://www.itia.info/assets/files/newsletters/Newsletter_2011_06.pdf Tungsten Chemicals and their Applications]''. Brochure by International Tungsten Industry Association.</ref>

<ref name=leew2000>{{cite journal|doi=10.1007/s11664-000-0139-8|title=Effects of surface porosity on tungsten trioxide(WO3) films' electrochromic performance|year=2000|last1=Lee|first1=W. J.|last2=Fang|first2=Y. K.|last3=Ho|first3=Jyh-Jier|last4=Hsieh|first4=W. T.|last5=Ting|first5=S. F.|last6=Huang|first6=Daoyang|last7=Ho|first7=Fang C.|journal=Journal of Electronic Materials|volume=29|issue=2|pages=183–187|bibcode=2000JEMat..29..183L|s2cid=98302697}}</ref>

</references>

==External links==
*[http://www.itia.info International Tungsten Industry Association]
*[http://www.rsc.org/publishing/journals/JM/article.asp?doi=jm9930300833 Preparation of tungsten trioxide electrochromic films]
*[http://www.sigmaaldrich.com/catalog/search/ProductDetail/ALDRICH/204781 Sigma Aldrich (supplier)]

{{Tungsten compounds}}
{{Oxides}}

{{DEFAULTSORT:Tungsten Trioxide}}
[[Category:Tungsten compounds]]
[[Category:Transition metal oxides]]