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Tellurium dioxide
Other names	Tellurium(IV) oxide
Identifiers
CAS number	7446-07-3
Properties
Molecular formula	TeO2
Molar mass	159.60 g/mol
Appearance	white solid
Density	5.670 g/cm3 (tetragonal); 6.04 g/cm3 (orthorhombic)
Melting point	733 °C
Boiling point	1245 °C
Solubility in water	negligible
Solubility	soluble in acid and alkali
Hazards
EU Index	Not listed
Flash point	Non-flammable
Related compounds
Other cations	Sulfur dioxide; Selenium dioxide
Related tellurium oxides	Tellurium trioxide
	(what is this?) (verify); Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
	Infobox references

Tellurium dioxide (TeO₂) is a solid oxide of tellurium. It is encountered in two different forms, the yellow orthorhombic mineral tellurite, β-TeO₂, and the synthetic, colourless tetragonal (paratellurite), α-TeO₂.^[2] Most of the information regarding reaction chemistry has been obtained in studies involving paratellurite, α-TeO₂.^[3]

[edit] Preparation

Paratellurite, α-TeO₂, is produced by reacting tellurium with O₂:^[2]

Te + O₂ → TeO₂

An alternative preparation is to dehydrate tellurous acid, H₂TeO₃, or to thermally decompose basic tellurium nitrate,Te₂O₄.HNO₃ above 400°C.^[2]

[edit] Chemical properties

TeO₂ is highly insoluble in water and soluble in concentrated sulfuric acid. It is also incompatible with strong acids and strong oxidizing agents. It is an amphoteric substance and therefore can act both as an acid or as a base depending on the solution it is in.^[4]

[edit] Structure

Paratellurite, α-TeO₂, converts at high pressure into the β-, tellurite form.^[5] 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 is 140°. α-TeO₂ In tellurite pairs of trigonal pyramidal, TeO₄ units, sharing an edge, share vertices to then form a layer.^[5] The shortest Te-Te distance in tellurite is 317 pm, compared to 374 pm in paratellurite.^[5] Similar Te₂O₆ units are found in the mineral denningite.^[5]

[edit] Uses

It is used as an acousto-optic material.

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. 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.^[6]

[edit] Safety information

TeO₂ is a possible teratogen.^[7]

It produces a garlic-like odour on the breath.

[edit] References

^ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0070494398
^ ^a ^b ^c Greenwood, Norman N.; Earnshaw, A. (1984), Chemistry of the Elements, Oxford: Pergamon, p. 911, ISBN 0-08-022057-6
^ W.R.McWhinnie (1995) Tellurium - Inorganic chemistry Encyclopedia of Inorganic Chemistry Ed. R. Bruce King (1994) John Wiley & Sons ISBN 0 471 93620 0
^ K. W. Bagnall (1966). The Chemistry of Selenium, Tellurium and Polonium. London: Elsevier. pp. 59–60.
^ ^a ^b ^c ^d Wells, A. F. (1984), Structural Inorganic Chemistry (5th ed.), Oxford: Clarendon Press, ISBN 0-19-855370-6
^ 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
^ 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.[1]

[edit] External links

[0] Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0070494398

[Greenwood-1] Greenwood, Norman N.; Earnshaw, A. (1984), Chemistry of the Elements, Oxford: Pergamon, p. 911, ISBN 0-08-022057-6

[McWhinnie-2] W.R.McWhinnie (1995) Tellurium - Inorganic chemistry Encyclopedia of Inorganic Chemistry Ed. R. Bruce King (1994) John Wiley & Sons ISBN 0 471 93620 0

[3] K. W. Bagnall (1966). The Chemistry of Selenium, Tellurium and Polonium. London: Elsevier. pp. 59–60.

[Wells-4] Wells, A. F. (1984), Structural Inorganic Chemistry (5th ed.), Oxford: Clarendon Press, ISBN 0-19-855370-6

[5] 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

[6] 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.[1]

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