Floating-zone growth of brownmillerite Sr2Fe2O5 and the observation of a chain-ordered superstructure by single-crystal neutron diffraction

► First floating-zone crystal growth of Sr2Fe2O5. ► The crystal is partially twinned but still has a unique axis. ► Single crystal neutron diffraction shows a supercell with a doubled c axis. ► Tetrahedral chains are long-range ordered at room temperature.