Tellurium trioxide

Tellurium trioxide (TeO3) is an inorganic chemical compound of tellurium and oxygen. In this compound, tellurium is in the +6 oxidation state.

Polymorphs
There are two forms, yellow-red α-TeO3 and grey, rhombohedral, β-TeO3 which is less reactive.

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.