A process is provided for preparing a powder of an oxide of at least one metal, each metal having an oxidation number between (III) and (VI). This process comprises successively and in this order: (a) reacting, with a compound comprising a hydroxide, an aqueous solution comprising, for each metal, at least one salt of the cation of said metal, (b) separating the precipitate obtained, (c) contacting the separated precipitate with an organic protic polar solvent, (d) removing the organic protic polar solvent by vacuum drying the precipitate. A process is further provided for manufacturing a pellet of an oxide of at least one metal as well as to a powder and to a pellet obtained according to these processes and to uses thereof.