Combined powder neutron and X-ray diffraction study of charge and orbital order in Bi0.75Sr0.25MnO3

The room temperature structure of Bi0.75Sr0.25MnO3 has been fitted to high-resolution synchrotron X-ray and time-of-flight neutron powder diffraction data. Constrained structural models were refined using a image Pn11 supercell (image, image, image, and image) of the underlying Pnma perovskite structure. The best-fit model evidences a 3:1 Mn3+/Mn4+charge ordering with only 30% of the ideal separation of bond valence sums. An ordered intergrowth of antiferro-orbitally ordered (LaMnO3 type) and charge and ferro-orbitally ordered (YBaMn2O6 type) blocks is observed. Off-centre Bi/Sr displacements are ferroelectrically ordered in this model.