Crystal Structures, Charge and Oxygen‐Vacancy Ordering in Oxygen Deficient Perovskites SrMnOx (x < 2.7)

Bulk SrMnO {sub x} samples with oxygen contents 2.5{<=}x<2.7 have been studied using a combination of neutron time-of-flight and high-energy high-resolution synchrotron X-ray diffraction measurements along with thermogravimetric analysis. We report the identification and characterization of two new oxygen-vacancy ordered phases, Sr{sub 5}Mn{sub 5}O{sub 13} (SrMnO{sub 2.6}-tetragonal P4/m a=8.6127(3) A, c=3.8102(2) A) and Sr{sub 7}Mn{sub 7}O{sub 19} (SrMnO{sub 2.714}-monoclinic P2/m a=8.6076(4) A, b=12.1284(4) A, c=3.8076(2) A, {gamma}=98.203(2){sup o}). The nuclear and magnetic structures of Sr{sub 2}Mn{sub 2}O{sub 5} are also reported (SrMnO{sub 2.5} nuclear: orthorhombic Pbam, magnetic: Orthorhombic Ay type P{sub c}bam with c {sub M}=2c). In the three phases, oxygen-vacancies are ordered in lines running along one of the (100) directions of the parent cubic perovskite system. Oxygen-vacancy ordering allows the charge and orbital ordering of the Mn{sup 3+} and Mn{sup 4+} cations in the new phases. - Graphical abstract: The structures of Sr{sub 5}Mn{sub 5}O{sub 13} and Sr{sub 7}Mn{sub 7}O{sub 19} (shown) were determined using synchrotron X-rays and neutron time-of-flight powder diffraction and the Rietveld method on multiphase bulk samples. Charge, orbital and oxygen vacancy-ordering has been observed in the novel compounds where Mn{sup 4+} octahedra and Mn{sup 3+} pyramids are linked through the corners leaving lines ofmore » vacant oxygen sites lying along the c-axis.« less