Phase relations and transport properties of undoped and La and/or Ti-doped Sr4Fe6O13 have been studied. In the doped materials significant amounts of perovskite SrFeO3-delta were formed together with SrFe12O19. An intergrowth on nanoscale of SrFeO3-delta and Sr4Fe6O13 was observed in the TEM for the La-doped material. The content of La was higher in the SrFeO3-delta than in the Sr4Fe6O13 phase. The electrical conductivity and chemical diffusion coefficient of undoped and La/Ti-doped Sr4Fe6O13 have been measured and a defect model for undoped Sr4Fe6O13 is presented. The transport properties of doped Sr4Fe6O13 reflect multiphase materials mainly dominated by the perovskite phase. (C) 2000 Elsevier Science B.V. All rights reserved.