View source for Tellurium dioxide

{{Chembox new
|   Name = Tellurium dioxide
|   ImageFile = Cryst struct teo2.png
|   ImageName = Tellurium dioxide
|   OtherNames = Tellurium(IV) oxide
| Section1 = {{Chembox Identifiers
|   CASNo = 7446-07-3
  }}
| Section2 = {{Chembox Properties
|   Formula = TeO<sub>2</sub>
|   MolarMass = 159.60 g/mol
|   Appearance = White solid
|   Density = 5.670 g/cm<sup>3</sup>
|   Solvent = other solvents
|   SolubleOther = Highly insoluble
|   MeltingPt = 733 °C
|   BoilingPt = 1245 °C}}
}}
{{CMG}}



'''Tellurium dioxide''' (TeO<sub>2</sub>) is a solid [[oxide]] of [[tellurium]]. It is encountered in two different forms, the yellow orthorhombic mineral [[tellurite]],β-TeO<sub>2</sub>, and the synthetic, colourless tetragonal (paratellurite), α-TeO<sub>2</sub>.<ref name = "Greenwood">{{Greenwood&Earnshaw}}</ref>  Most of the information regarding reaction chemistry has been obtained in studies involving paratellurite,  α-TeO<sub>2</sub>.<ref name = “McWhinnie”> W.R.McWhinnie (1995) ''Tellurium - Inorganic chemistry''  Encyclopedia of Inorganic Chemistry Ed. R. Bruce King (1994) John Wiley & Sons ISBN 0 471 93620 0 </ref>

==Preparation==
Paratellurite,α-TeO<sub>2</sub>, is produced by reacting tellurium with [[dioxygen|O<sub>2</sub>]]:<ref name = "Greenwood"/>
:Te + O<sub>2</sub> → TeO<sub>2</sub>
An alternative preparation is to dehydrate tellurous acid, H2TeO3, or to thermally decompose [[basic tellurium nitrate]],Te<sub>2</sub>O<sub>4</sub>.HNO<sub>3</sub> above 400°C.<ref name = "Greenwood"/>

==Chemical properties==
TeO<sub>2</sub> is highly [[insoluble]] in [[water]] and completely insoluble in concentrated [[sulfuric acid]].
It is also incompatible with strong [[acid]]s and strong [[oxidizing agent]]s. It is an [[amphoteric]] substance and therefore can act both as an acid or as a base depending on the solution it is in.

==Structure==
Paratellurite,α-TeO<sub>2</sub>, converts at high pressure into the β-, tellurite form.<ref name = "Wells">Wells A.F. (1984) ''Structural Inorganic Chemistry'' 5th edition Oxford Science Publications ISBN 0-19-855370-6</ref> Both the α-, (paratellurite) and β- (tellurite forms) contain four coordinate Te with the oxygen atoms at four of the corners of a trigonal bipyramid. In paratellurite all vertices are shared to give a [[titanium dioxide|rutile]]-like structure, where the O-Te-O bond angle is 140°.α-TeO<sub>2</sub> In tellurite pairs of trigonal pyramidal, TeO<sub>4</sub> units, sharing an edge, share vertices to then form a layer.<ref name = "Wells"/> The shortest Te-Te distance in tellurite is 317 pm, compared to 374 pm in paratellurite.<ref name = "Wells"/> Similar Te<sub>2</sub>O<sub>6</sub> units are found in the mineral [[denningite]].<ref name = "Wells"/>

==Uses==
It is used as an [[acousto-optic]] material.<br />

Tellurium dioxide is also a conditional glass former, which means it will form a glass with small molar% additions of a second compound such as an oxide or halide. TeO<sub>2</sub> glasses have high [[refractive indices]] and transmit into the mid-[[infrared]] part of the [[electromagnetic spectrum]], therefore they are of technological interest for [[optical waveguide]]s. Tellurite glasses have also been shown to exhibit [[Raman]] gain up to 30 times that of [[silica]], useful in [[optical fibre]] amplification.<ref>
 Tellurite glasses with peak absolute Raman gain coefficients up to 30 times that of fused silica, R Stegeman, L Jankovic, H Kim, C Rivero, G Stegeman, K Richardson, P Delfyett, Y Guo, A Schulte, T Cardinal, Optics Letters, 28, 13, 1126-1128, {{doi|10.1364/OL.28.001126}}</ref>

==Safety information==
TeO<sub>2</sub> is a possible [[teratogen]].<ref>Maternal toxicity and teratogenicity of tellurium dioxide in the Wistar rat: relationship to pair-feeding.
Perez-D'Gregorio R E, Miller R K, Baggs R B.Reprod Toxicol. 1988;2(1):55-61.[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2980402&dopt=Abstract]</ref>

It produces a [[garlic]]-like odour on the breath.

==References==
K. W. Bagnall, ''The Chemistry of Selenium, Tellurium and Polonium'', pp 59-60, Elsevier, London, 1966.
{{reflist}}

==External links==
*[http://www.mt-berlin.com/frames_ao/descriptions/teo2.htm Moltech Berlin]
*[http://acoustooptics.phys.msu.su/ Mоscow State University]
*[http://www.sciencedirect.com/science?_ob=ArticleURL&_aset=V-WA-A-W-W-MsSAYZA-UUA-U-AAWYZWADCZ-AAWZWUWCCZ-BWWCDADBC-W-U&_rdoc=2&_fmt=summary&_udi=B6TXP-46JYHGM-2V&_coverDate=08%2F31%2F1994&_cdi=5596&_orig=search&_st=13&_sort=d&view=c&_acct=C000030198&_version=1&_urlVersion=0&_userid=590719&md5=c5ace3692ad48f9552459a5cb049c841 J. S. Wang, E. M. Vogel and E. Snitzer "Tellurite glass: a new candidate for fiber devices" ''Opt. Mat.'' 3 (3) 187-203 1994]
*[http://physchem.ox.ac.uk/MSDS/TE/tellurium_dioxide.html TeO<sub>2</sub> MSDS]

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[[Category:Oxides]]
[[Category:Tellurium compounds]]
[[Category:Nonlinear optical materials]]
[[Category:Crystals]]

[[de:Tellurdioxid]]
[[ja:二酸化テルル]]



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