title: Identifying the local structural units in La0.5Ba0.5MnO2.5and BaY0.25Fe0.75O2.5through the neutron pair distribution function.
abstract: Neutron pair distribution function data are used to investigate the local structures of two oxygen deficient perovskites with simple cubic crystal structures. La0.5Ba0.5MnO2.5is found to have alternating layers of MnO6octahedra and MnO4tetrahedra, making it similar to other members of the La1-xBaxMnO2.5series with smaller x values which have brownmillerite crystal structures. Our fitting results suggest that La0.5Ba0.5MnO2.5is not locally similar to any one brownmillerite structure type but instead has a variety of intra-layer and inter-layer relationships. We propose that this could be due to short range segregation of the much differently sized La3+and Ba2+cations, which creates significantly different inter-layer distances. BaY0.25Fe0.75O2.5is found not to have a brownmillerite-type local structure but rather seems to consist of structural units which are similar to Ba3YFe2O7.5, an earlier member of the BanYFen-1O2.5nseries. The PDF analysis shows that there are never neighboring Y atoms and that the O vacancies lie exclusively between Fe atoms, such that Y is always octahedrally coordinated. The PDF also suggests that there are more tetrahedral Fe than expected, which could be due to the presence of terminal O atoms in Fe centered dimeric units, similar to what is found in Ba3YFe2O7.5.
authors.affiliation: Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA. gmkchemist@gmail.com.
authors.forename: Graham
authors.identifier: http://orcid.org/0000-0003-1886-7254
authors.initials: G
authors.lastname: King
authors.affiliation: Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907, USA and Department of Chemistry and Brockhouse Institute of Materials Research, McMaster University, Hamilton, ON L8S 4M1, Canada.
authors.forename: Corey M
authors.identifier: http://orcid.org/0000-0003-3262-5366
authors.initials: CM
authors.lastname: Thompson
authors.affiliation: Department of Chemistry, University of Oxford, Inorganic Chemistry Laboratory, South Parks Road, Oxford, OX1 3QR, UK.
authors.forename: Kun
authors.identifier: http://orcid.org/0000-0002-5754-0222
authors.initials: K
authors.lastname: Luo
authors.affiliation: Department of Chemistry and Brockhouse Institute of Materials Research, McMaster University, Hamilton, ON L8S 4M1, Canada.
authors.forename: John E
authors.identifier: http://orcid.org/0000-0003-1307-8379
authors.initials: JE
authors.lastname: Greedan
authors.affiliation: Department of Chemistry, University of Oxford, Inorganic Chemistry Laboratory, South Parks Road, Oxford, OX1 3QR, UK.
authors.forename: Michael A
authors.identifier: http://orcid.org/0000-0002-6248-2063
authors.initials: MA
authors.lastname: Hayward