Characterization of SrBiMn2−xTixO6 perovskites: Local ordering influence on the dielectric and magnetic response

Two new phases in the (SrTiO3)-(BiMnO3) perovskite type system were studied. These SrBiMn2−xTixO6 (x=0.5 and 0.75) ceramics were prepared by the liquid-mix method as polycrystalline powders. They were characterized by neutron diffraction (ND), electrical and magnetic measurements and these results were analysed in connection with the x=0.25 phase, previously described by us. Their crystal structures were fitted in the tetragonal I4/mcm space group, with additional superstructure reflections suggesting local ordering. Electron microscopy results revealed these ordering effects are actually present concerning both perovskite sublattices. The electrical response pointed to a mechanism consisting in variable range hopping of polarons. A relaxor ferroelectric behaviour dependent on the pellets thickness was found with Tm in the 140–240 K range. The magnetic structures imply an incommensurable modulation of the magnetic moments along the c or a directions, depending on the substitution degree x. A cluster picture in terms of chemically different nanoregions responsible of the macroscopic response is discussed.