Protactinium(V) oxide is a chemical compound with the formula Pa<sub>2</sub>O<sub>5</sub>. When it is reduced with hydrogen, it forms PaO<sub>2</sub>. Aristid V. Grosse was first to prepare 2 mg of Pa<sub>2</sub>O<sub>5</sub> in 1927. Pa<sub>2</sub>O<sub>5</sub> does not dissolve in concentrated HNO<sub>3</sub>, but dissolves in HF and in a HF + H<sub>2</sub>SO<sub>4</sub> mixture and reacts at high temperatures with solid oxides of alkali metal and alkaline earth metals.
As protactinium(V) oxide, like other protactinium compounds, is radioactive, toxic and very rare, it has very limited technological use. Mixed oxides of Nb, Mg, Ga and Mn, doped with 0.005âÂÂ0.52% Pa<sub>2</sub>O<sub>5</sub>, have been used as high temperature dielectrics (up to 1300 ðC) for ceramic capacitors.