Bi0.75Sr0.25FeO3−δ : Revealing order/disorder phenomena by combining diffraction techniques

The local and long range structure of polycrystalline samples of Bi0.75Sr0.25FeO3−δ has been probed by neutron and synchrotron X-ray diffraction coupled with transmission electron microscopy. It is found that the long range structure on average can be described by the cubic space group P m - 3 m ( a p ≅ 3.951 Å ). However, the refinements revealed large atomic displacements for the (Bi, Sr) cations and the oxygen atoms from their ideal positions. The electron microscopy study indicates the existence of local phenomena like local ordering of oxygen vacancies, which are segregated at the randomly spaced parallel (FeO2−δ) planes, or the existence of region of different symmetry, probably R 3 c . At room temperature, the compound exhibits G-type antiferromagnetism ( T N ≅ 650 K ) with a magnetic moment of ≅ 3.7 μ B .