Phase evolution of bismuth ferrites in the process of hydrothermal reaction

► Sillenite Bi25FeO40 is the intermediate phase in the formation of pervoskite BiFeO3. ► Phase evolution can be controlled by adjusting the process parameters. ► The dissolution of Fe(OH)3 plays an important role to control the phase evolution of bismuth ferrites. ► The formation of perovskite BiFeO3 crystallites was based on the dissolution of sillenite Bi25FeO40.