Tellurium trioxide ( Te O₃) is an

inorganic In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemist ...

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

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 occasionall ...

and

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...

. In this compound, tellurium is in the +6

oxidation state In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ...

Polymorphs

There are two forms, yellow-red α-TeO₃ and grey, rhombohedral, β-TeO₃ which is less reactive.''Inorganic Chemistry'',Egon Wiberg, Arnold Frederick Holleman Elsevier 2001
α-TeO₃ has a structure similar to FeF₃ with octahedral TeO₆ units that share all vertices.

Preparation

α-TeO₃ can be prepared by heating orthotelluric acid, Te(OH)₆, at over 300 °C. The β-TeO₃ form can be prepared by heating α-TeO₃ in a sealed tube with O₂ and H₂SO₄.
α-TeO₃ is unreactive to water but is a powerful oxidising agent when heated. With alkalis it forms tellurates.
α-TeO₃ when heated loses oxygen to form firstly Te₂O₅ and then TeO₂.

References

Oxides Tellurium(VI) compounds Interchalcogens {{inorganic-compound-stub