| Autor: |
King G; Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA. gmkchemist@gmail.com., Thompson CM; 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., Luo K; Department of Chemistry, University of Oxford, Inorganic Chemistry Laboratory, South Parks Road, Oxford, OX1 3QR, UK., Greedan JE; Department of Chemistry and Brockhouse Institute of Materials Research, McMaster University, Hamilton, ON L8S 4M1, Canada., Hayward MA; Department of Chemistry, University of Oxford, Inorganic Chemistry Laboratory, South Parks Road, Oxford, OX1 3QR, UK. |
| Abstrakt: |
Neutron pair distribution function data are used to investigate the local structures of two oxygen deficient perovskites with simple cubic crystal structures. La 0.5 Ba 0.5 MnO 2.5 is found to have alternating layers of MnO 6 octahedra and MnO 4 tetrahedra, making it similar to other members of the La 1-x Ba x MnO 2.5 series with smaller x values which have brownmillerite crystal structures. Our fitting results suggest that La 0.5 Ba 0.5 MnO 2.5 is 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 La 3+ and Ba 2+ cations, which creates significantly different inter-layer distances. BaY 0.25 Fe 0.75 O 2.5 is found not to have a brownmillerite-type local structure but rather seems to consist of structural units which are similar to Ba 3 YFe 2 O 7.5 , an earlier member of the Ba n YFe n-1 O 2.5n series. 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 Ba 3 YFe 2 O 7.5 . |
