Diphosphorus tetroxide, or phosphorus tetroxide is an inorganic compound of phosphorus and oxygen. It has the empirical chemical formula . Solid phosphorus tetroxide (also referred to as phosphorus(III,V)-oxide) consists of variable mixtures of the mixed-valence oxides P<sub>4</sub>O<sub>7</sub>, P<sub>4</sub>O<sub>8</sub> and P<sub>4</sub>O<sub>9</sub>.
Phosphorus tetroxide can be produced by thermal decomposition of phosphorus trioxide, which disproportionates above 210 ðC to form phosphorus tetroxide, with elemental phosphorus as a byproduct:
In addition, phosphorus trioxide can be converted into phosphorus tetroxide by controlled oxidation with oxygen in carbon tetrachloride solution.
Careful reduction of phosphorus pentoxide with red phosphorus at 450-525 ðC also produces phosphorus tetroxide.