Tellurium dioxide

Paratellurite, α-TeO₂, is produced by reacting tellurium with O₂:

:Te + O₂ → TeO₂

An alternative preparation is to dehydrate tellurous acid, H₂TeO₃, or to thermally decompose basic tellurium nitrate, Te₂O₄·HNO₃, above 400 °C.

The longitudinal speed of sound in Tellurium dioxide is {{convert|4260|m/s}} at around room temperature.{{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}}

TeO₂ is barely soluble in water and soluble in strong acids and alkali metal hydroxides.{{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}} It is an amphoteric substance and therefore can act both as an acid or as a base depending on the solution it is in.{{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 }} It reacts with acids to make tellurium salts and bases to make tellurites. It can be oxidized to telluric acid or tellurates.

The tellurite ion is kinetically inert, but TeO₂ equivalents will oxidize thioates in acid to the diacyl disulfide.{{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), C₁₄H₁₀O₂S₂Te(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 }}

Paratellurite, α-TeO₂, converts at high pressure into the β-, tellurite form.{{Wells5th}} 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 rutile-like structure, where the O-Te-O bond angle are 140°. α-TeO₂ In tellurite pairs of trigonal pyramidal, TeO₄ units, sharing an edge, share vertices to then form a layer. The shortest Te-Te distance in tellurite is 317 pm, compared to 374 pm in paratellurite. Similar Te₂O₆ units are found in the mineral denningite.

{{chem|TeO|2}} melts at 732.6 °C, forming a red liquid.{{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}} 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 TeO₂ glass as distinct from the canonical single-oxide glass-formers such as SiO₂, which share the same short-range order with their parent liquids.{{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 }}

It is used as an acousto-optic material.

Tellurium dioxide is also a reluctant glass former, it will form a glass under suitable cooling conditions,{{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 }} or with additions of a small molar fraction of a second compound such as an oxide or halide. TeO₂ glasses have high refractive indices and transmit into the mid-infrared part of the electromagnetic spectrum, therefore they are of technological interest for optical waveguides. Tellurite glasses have also been shown to exhibit Raman gain up to 30 times that of silica, useful in optical fibre amplification.{{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 }}

TeO₂ is a possible teratogen.{{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 }}

Exposure to tellurium compounds produces a garlic-like odour on the breath, caused by the formation of diethyl telluride.{{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}}

{{reflist}}

• [http://www.mt-berlin.com/frames_ao/descriptions/teo2.htm TeO₂ properties at Moltech Berlin]
• [http://physchem.ox.ac.uk/MSDS/TE/tellurium_dioxide.html Safety data for TeO₂] {{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