Antimony tetroxide is an inorganic compound with the formula Sb<sub>2</sub>O<sub>4</sub>. This material, which exists as the mineral cervantite, is white but reversibly yellows upon heating. The material, with empirical formula SbO<sub>2</sub>, is called antimony tetroxide to signify the presence of two kinds of Sb centers.
The material forms when Sb<sub>2</sub>O<sub>3</sub> is heated in air:
At 800 ðC, antimony(V) oxide loses oxygen to give the same material:
The material is mixed valence, containing both Sb(V) and Sb(III) centers. Two polymorphs are known, one orthorhombic (shown in the infobox) and one monoclinic. Both forms feature octahedral Sb(V) centers arranged in sheets with distorted Sb(III) centers bound to four oxides.