Tellurium dioxide (TeO₂) is a solid

oxide An oxide () is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– (molecular) ion. with oxygen in the oxidation state of −2. Most of the E ...

tellurium Tellurium is a chemical element with the symbol Te and atomic number 52. It is a brittle, mildly toxic, rare, silver-white metalloid. Tellurium is chemically related to selenium and sulfur, all three of which are chalcogens. It is occasionally fou ...

. It is encountered in two different forms, the yellow orthorhombic mineral

tellurite The tellurite ion is . A tellurite (compound), for example sodium tellurite, is a compound that contains this ion. They are typically colorless or white salts, which in some ways are comparable to sulfite. A mineral with the formula TeO2 is ...

, β-TeO₂, and the synthetic, colourless tetragonal (paratellurite), α-TeO₂. Most of the information regarding reaction chemistry has been obtained in studies involving paratellurite, α-TeO₂.W.R.McWhinnie (1995) ''Tellurium - Inorganic chemistry'' Encyclopedia of Inorganic Chemistry Ed. R. Bruce King (1994) John Wiley & Sons

Preparation

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.

Physical properties

The longitudinal speed of sound in Tellurium dioxide is at around room temperature.

Chemical properties

TeO₂ is barely soluble in

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...

and soluble in strong acids and

alkali metal hydroxide The alkali hydroxides are a class of chemical compounds which are composed of an alkali metal cation and the hydroxide anion (OH−). The alkali hydroxides are: *Lithium hydroxide (LiOH) * Sodium hydroxide (NaOH) *Potassium hydroxide (KOH) *Rubi ...

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. It reacts with acids to make tellurium salts and bases to make

s. It can be oxidized to

telluric acid Telluric acid is a chemical compound with the formula , often written as . It is a white crystalline solid made up of octahedral molecules which persist in aqueous solution. In the solid state, there are two forms, rhombohedral and monoclinic, a ...

tellurate In chemistry tellurate is a compound containing an oxyanion of tellurium where tellurium has an oxidation number of +6. In the naming of inorganic compounds it is a suffix that indicates a polyatomic anion with a central tellurium atom.

Structure

Paratellurite, α-TeO₂, converts at high pressure into the β-, tellurite form. 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. melts at 732.6 °C, forming a red liquid. 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.

Uses

It is used as an

acousto-optic Acousto-optics is a branch of physics that studies the interactions between sound waves and light waves, especially the diffraction of laser light by ultrasound (or sound in general) through an ultrasonic grating. Introduction Optics has had a v ...

material. Tellurium dioxide is also a reluctant glass former, it will form a glass under suitable cooling conditions, or 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 Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

part of the

electromagnetic spectrum The electromagnetic spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies. The electromagnetic spectrum covers electromagnetic waves with frequencies ranging from ...

, 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 Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...

, useful in

optical fibre An optical fiber, or optical fibre in Commonwealth English, is a flexible, transparent fiber made by drawing glass (silica) or plastic to a diameter slightly thicker than that of a human hair. Optical fibers are used most often as a means to ...

amplification.

Safety

TeO₂ is a possible teratogen. Exposure to tellurium compounds produces a

garlic Garlic (''Allium sativum'') is a species of bulbous flowering plant in the genus ''Allium''. Its close relatives include the onion, shallot, leek, chive, Allium fistulosum, Welsh onion and Allium chinense, Chinese onion. It is native to South A ...

-like odour on the breath, caused by the formation of ethyl telluride.

References

External links

TeO₂ properties at Moltech Berlin
{{Oxides Oxides Tellurium(IV) compounds Nonlinear optical materials Interchalcogens