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 α-TeO2, paratellurite | |
| Names | |
|---|---|
| Other names Tellurium(IV) oxide | |
| Identifiers | |
3D model (JSmol) | |
| ChemSpider |
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| ECHA InfoCard | 100.028.357 |
| UNII | |
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| Properties | |
| TeO2 | |
| Molar mass | 159.60 g/mol |
| Appearance | white solid |
| Density | 5.670 g/cm3(orthorhombic) 6.04 g/cm3 (tetragonal)[1] |
| Melting point | 732 °C (1,350 °F; 1,005 K) |
| Boiling point | 1,245 °C (2,273 °F; 1,518 K) |
| negligible | |
| Solubility | soluble inacid andalkali |
Refractive index (nD) | 2.24 |
| Hazards | |
| Flash point | Non-flammable |
| Related compounds | |
Othercations | Sulfur dioxide Selenium dioxide |
| Tellurium trioxide Tellurium monoxide | |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Tellurium dioxide (TeO2) is a solidoxide oftellurium. It is encountered in two different forms, the yellow orthorhombic mineraltellurite, 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]
Paratellurite, α-TeO2, is produced by reacting tellurium withO2:[2]
An alternative preparation is to dehydrate tellurous acid, H2TeO3, or to thermally decomposebasic tellurium nitrate, Te2O4·HNO3, above 400 °C.[2]
The longitudinal speed of sound in Tellurium dioxide is 4,260 metres per second (14,000 ft/s) at around room temperature.[4]
TeO2 is barelysoluble inwater and soluble instrong acids andalkali metal hydroxides.[5] It is anamphoteric substance and therefore can act both as an acid or as a base depending on the solution it is in.[6] It reacts with acids to make tellurium salts and bases to maketellurites. It can be oxidized totelluric acid ortellurates.
The tellurite ion is kinetically inert, but TeO2 equivalents will oxidizethioates in acid to the diacyl disulfide.[7]
Paratellurite, α-TeO2, converts at high pressure into the β-, tellurite form.[8] 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 arutile-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.[8] The shortest Te-Te distance in tellurite is 317 pm, compared to 374 pm in paratellurite.[8] Similar Te2O6 units are found in the mineraldenningite.[8]
TeO
2 melts at 732.6 °C, forming a red liquid.[9] 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.[10]
It is used as anacousto-optic material.[4]
Tellurium dioxide is also a reluctant glass former, it will form a glass under suitable cooling conditions,[11] or with additions of a smallmolar fraction of a second compound such as an oxide or halide. TeO2 glasses have highrefractive indices and transmit into the mid-infrared part of theelectromagnetic spectrum, therefore they are of technological interest foroptical waveguides. Tellurite glasses have also been shown to exhibitRaman gain up to 30 times that ofsilica, useful inoptical fibre amplification.[12]
TeO2 is a possibleteratogen.[13]
Exposure to tellurium compounds produces agarlic-like odour on the breath, caused by the formation ofdiethyl telluride.[14]
