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

摘要

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 (1/2 00) Pn11 supercell (a = 11.0286(2) angstrom, b = 7.7351 (1) angstrom, c = 5.53419(9) angstrom, and alpha = 89.894( 1)degrees) of the underlying Pinna 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. (C) 2006 Elsevier Inc. All rights reserved.