View source for Tellurium dioxide

{{cs1 config|name-list-style=vanc}}
{{chembox
| Watchedfields = changed
| verifiedrevid = 470481455
| Name = Tellurium dioxide
| ImageFile = TeO2powder.jpg
| ImageFile2 = Cryst struct teo2.png
| ImageCaption2 = α-TeO<sub>2</sub>, paratellurite
| IUPACName = 
| OtherNames = Tellurium(IV) oxide
|Section1={{Chembox Identifiers
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 56390
| PubChem = 62638
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 397E9RKE83
| InChI = 1/O2Te/c1-3-2
| InChIKey = LAJZODKXOMJMPK-UHFFFAOYAO
| SMILES = O=[Te]=O
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/O2Te/c1-3-2
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = LAJZODKXOMJMPK-UHFFFAOYSA-N
| CASNo = 7446-07-3
| CASNo_Ref = {{cascite|correct|CAS}}
  }}
|Section2={{Chembox Properties
| Formula = TeO<sub>2</sub>
| MolarMass = 159.60 g/mol
| Appearance = white solid
| Density = 5.670 g/cm<sup>3</sup>([[orthorhombic]]) <br /> 6.04 g/cm<sup>3</sup>  ([[tetragonal]]) <ref>{{cite book |author=Pradyot Patnaik
| title =Handbook of Inorganic Chemicals |publisher=McGraw-Hill |year=2002 |isbn=0-07-049439-8}}</ref>
| Solubility = negligible
| SolubleOther = soluble in [[acid]] and [[alkali]]
| MeltingPtC = 732
| BoilingPtC = 1245
| RefractIndex = 2.24
  }}
|Section7={{Chembox Hazards
| ExternalSDS = 
| HPhrases = 
| PPhrases = 
| GHS_ref  = 
| NFPA-H = 
| NFPA-F = 
| NFPA-R = 
| NFPA-S = 
| FlashPt = Non-flammable
| LD50 = 
| PEL = 
  }}
|Section8={{Chembox Related
| OtherAnions = 
| OtherCations = [[Sulfur dioxide]]<br />[[Selenium dioxide]]
| OtherFunction = [[Tellurium trioxide]]<br />[[Tellurium monoxide]]
| OtherFunction_label = [[tellurium]] [[oxide]]s
| OtherCompounds = 
 }}
}}
'''Tellurium dioxide''' (TeO<sub>2</sub>) is a solid [[oxide]] of [[tellurium]]. It is encountered in two different forms, the yellow orthorhombic mineral [[tellurite (mineral)|tellurite]], β-TeO<sub>2</sub>, and the synthetic, colourless tetragonal (paratellurite), α-TeO<sub>2</sub>.<ref name = "Greenwood">{{Greenwood&Earnshaw1st|page=911}}</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|978-0-471-93620-6}}</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, H<sub>2</sub>TeO<sub>3</sub>, or to thermally decompose [[basic tellurium nitrate]], Te<sub>2</sub>O<sub>4</sub>·HNO<sub>3</sub>, above 400&nbsp;°C.<ref name = "Greenwood"/>

==Physical properties==

The longitudinal speed of sound in Tellurium dioxide is {{convert|4260|m/s}} at around room temperature.<ref name="Intra">{{cite web|url=https://intraaction.com/wp-content/themes/Divi/pdf/ATMModSeries08991.pdf|title=MODEL ATM SERIES ACOUSTO-OPTIC MODULATOR|website=Intraaction.com|access-date=14 March 2022}}</ref>

==Chemical properties==
TeO<sub>2</sub> is barely [[soluble]] in [[water]] and soluble in [[acid|strong acids]] and [[alkali metal hydroxide]]s.<ref>{{cite book |author=Mary Eagleson |title=Concise Encyclopedia Chemistry |url=https://archive.org/details/conciseencyclope00eagl |url-access=registration |pages=1081 |publisher=Walter de Gruyter |location=Berlin |year=1994 |isbn=3-11-011451-8}}</ref> It is an [[amphoteric]] substance and therefore can act both as an acid or as a base depending on the solution it is in.<ref>{{cite book |author=K. W. Bagnall |title=The Chemistry of Selenium, Tellurium and Polonium |pages=[https://archive.org/details/chemistryofsulph0000unse/page/59 59–60] |publisher=Elsevier |location=London |year=1966 |isbn=0-08-018855-9 |url=https://archive.org/details/chemistryofsulph0000unse/page/59 }}</ref> It reacts with acids to make tellurium salts and bases to make [[tellurite (ion)|tellurite]]s. It can be oxidized to [[telluric acid]] or [[tellurate]]s.

The tellurite ion is kinetically inert, but TeO<sub>2</sub> equivalents will oxidize [[thiocarboxylic acid|thioate]]s in acid to the diacyl disulfide.<ref>{{cite journal|doi=10.1007/BF01161161|journal=Journal of Crystallographic and Spectroscopic Research|volume=14|issue=3|year=1984|title=Synthesis, properties, and molecular structure of bis(thiobenzoato-S)tellurium(II), C<sub>14</sub>H<sub>10</sub>O<sub>2</sub>S<sub>2</sub>Te(II)|first1=T.|last1=Subrahmanyan|first2=G.|last2=Aravamudan|first3=G. C.|last3=Rout|first4=M.|last4=Seshasayee|orig-date=18 March 1983|publisher=Plenum|pages=242–243|bibcode=1984JCCry..14..239S }}</ref>

==Structure==
Paratellurite, α-TeO<sub>2</sub>, converts at high pressure into the β-, tellurite form.<ref name = "Wells">{{Wells5th}}</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 are 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"/>

{{chem|TeO|2}} melts at 732.6&nbsp;°C, forming a red liquid.<ref name="wiberg_holleman">{{cite book|title = Inorganic chemistry|author1 = Egon Wiberg| author2 = Nils Wiberg|author3 = Arnold Frederick Holleman|publisher = Academic Press|year = 2001|isbn = 0-12-352651-5|pages = 592–593}}</ref>  The structure of the liquid, as well as the glass which can be formed from it with sufficiently rapid cooling, are also based on approximately four coordinate Te. However, compared to the crystalline forms, the liquid and glass appear to incorporate short-range disorder (a variety of coordination geometries) which marks TeO<sub>2</sub> glass as distinct from the canonical single-oxide glass-formers such as SiO<sub>2</sub>, which share the same short-range order with their parent liquids.<ref>{{cite journal |last1=Alderman |first1=Oliver |last2=Benmore |first2=Chris |last3=Feller |first3=Steve |last4=Kamitsos |first4=Efstratios |last5=Simandiras |first5=Emmanuel |last6=Liakos |first6=Dimitrios |last7=Jesuit |first7=Martha |last8=Boyd |first8=Makyla |last9=Packard |first9=Michael |last10=Weber |first10=Rick |title=Short-Range Disorder in TeO2 Melt and Glass |journal=J. Phys. Chem. Lett. |year=2020 |volume=11 |issue=2 |pages=427–431 |doi=10.1021/acs.jpclett.9b03231 |pmid=31867975 |osti=1591765 |s2cid=209446093 }}</ref>

==Uses==
It is used as an [[acousto-optic]] material.<ref name="Intra"/>

Tellurium dioxide is also a reluctant glass former, it will form a glass under suitable cooling conditions,<ref>{{cite journal |last1=Tagiara |first1=N. S. |last2=Palles |first2=D. |last3=Simandiras |first3=E. |last4=Psycharis |first4=V. |last5=Kyritsis |first5=A. |last6=Kamitsos |first6=E. I. |title=Synthesis, thermal and structural properties of pure TeO2 glass and zinc-tellurite glasses |journal=Journal of Non-Crystalline Solids |year=2017 |volume=457 |pages=116–125 |doi=10.1016/j.jnoncrysol.2016.11.033 }}</ref> or with additions of a small [[molar fraction]] 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 amplification|Raman gain]] up to 30 times that of [[silica]], useful in [[optical fibre]] amplification.<ref>{{cite journal |vauthors=Stegeman R, Jankovic L, Kim H, Rivero C, Stegeman G, Richardson K, Delfyett P, Guo Y, Schulte A, Cardinal T |title=Tellurite glasses with peak absolute Raman gain coefficients up to 30 times that of fused silica |journal=Optics Letters |volume=28 |issue=13 |pages=1126–8 |year=2003 |pmid=12879929 |doi=10.1364/OL.28.001126 |bibcode=2003OptL...28.1126S }}</ref>

==Safety==
TeO<sub>2</sub> is a possible [[teratogen]].<ref>{{cite journal |doi=10.1016/S0890-6238(88)80009-1 |vauthors=Perez-D'Gregorio RE, Miller RK, Baggs RB |title=Maternal toxicity and teratogenicity of tellurium dioxide in the Wistar rat: relationship to pair-feeding |journal=Reprod. Toxicol. |volume=2 |issue=1 |pages=55–61 |year=1988 |pmid=2980402 |bibcode=1988RepTx...2...55P }}</ref>

Exposure to tellurium compounds produces a [[garlic]]-like odour on the breath, caused by the formation of [[diethyl telluride]].<ref>{{cite book|title = Studies in Natural Products Chemistry, Volume 35|author = Atta-ur-Rahman| publisher = Elsevier|year = 2008| isbn = 978-0-444-53181-0|page = 905| url = https://books.google.com/books?id=8Ugmrew2EqEC}}</ref>

==References==
{{reflist}}

==External links==
*[http://www.mt-berlin.com/frames_ao/descriptions/teo2.htm TeO<sub>2</sub> properties at Moltech Berlin]
*[http://physchem.ox.ac.uk/MSDS/TE/tellurium_dioxide.html Safety data for TeO<sub>2</sub>] {{Webarchive|url=https://web.archive.org/web/20070109072244/http://physchem.ox.ac.uk/MSDS/TE/tellurium_dioxide.html |date=2007-01-09 }}

{{Tellurium compounds}}
{{Oxides}}

[[Category:Oxides]]
[[Category:Tellurium(IV) compounds]]
[[Category:Nonlinear optical materials]]
[[Category:Interchalcogens]]