Tellurium trioxide (TeO<sub>3</sub>) is an inorganic chemical compound of tellurium and oxygen. In this compound, tellurium is in the +6 oxidation state.
There are two forms, yellow-red ñ-TeO<sub>3</sub> and grey, rhombohedral, ò-TeO<sub>3</sub> which is less reactive.<br /> ñ-TeO<sub>3</sub> has a structure similar to FeF<sub>3</sub> with octahedral TeO<sub>6</sub> units that share all vertices.
ñ-TeO<sub>3</sub> can be prepared by heating orthotelluric acid, Te(OH)<sub>6</sub>, at over 300 ðC. The ò-TeO<sub>3</sub> form can be prepared by heating ñ-TeO<sub>3</sub> in a sealed tube with O<sub>2</sub> and H<sub>2</sub>SO<sub>4</sub>.<br /> ñ-TeO<sub>3</sub> is unreactive to water but is a powerful oxidising agent when heated. With alkalis it forms tellurates.<br /> ñ-TeO<sub>3</sub> when heated loses oxygen to form firstly Te<sub>2</sub>O<sub>5</sub> and then TeO<sub>2</sub>.