“Forbidden” reflections in neutron diffraction on bismuth metal oxides: symmetry reduction, λ/2 effect or Umweganregung?
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Johannes Birkenstock
,
Gwilherm Nénert
Abstract
Large crystals of Bi2M4O9 (M = Fe, Ga) were examined by single-crystal neutron diffraction at the Institut Laue Langevin (ILL) in Grenoble. The crystal structures of these bismuth metal oxides are commonly described as mullite-type compounds in space group Pbam. However, up to several hundreds of reflections were observed in both compounds with significant intensity violating the reflection conditions in this space group. Psi-scans with a short wavelength (0.837 Å at D9) were quasi-continuous and thus provided ambiguous results, hampering the identification of the source of these intensities. With a much longer wavelength (2.364 Å at D10) the Psi scans displayed strong variations of the intensities with small changes of the scan angle Psi. These Psi scan intensities could be well matched by an appropriate calculation with the program UMWEG (Rossmanith, 2003) and thus multiple diffraction turned out to be the source of these extra reflections. As a result the space group Pbam proved to be the correct one. Due to widespread misconceptions the geometrical background of Umweganregung is discussed to considerable detail.
References
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Articles in the same Issue
- Inhalt
- Author Index of Volume 228 Issues 1–11
- Symmetry and the polar state of condensed molecular matter
- “Forbidden” reflections in neutron diffraction on bismuth metal oxides: symmetry reduction, λ/2 effect or Umweganregung?
- The keyite crystal structure, revisited
- Liebau density vector: a new approach to characterize lone electron pairs in mullite-type materials
- Magnesium and cadmium in covalently bonded networks: synthesis and structure of AETMg and AETCd (AE = Ca, Sr; T = Pd, Ag, Pt, Au) with TiNiSi type structure and the solid solution Yb2–xPtMgx
- Synthesis and structure of RE2RuMg2 (RE = Dy, Ho, Er, Tm, Lu) – i5 superstructures of the bcc packing
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- Crystal structures of mefloquine-oxazolidine derivatives, 4-[3-(halophenyl)hexahydro[1,3]oxazolo[3,4-a]pyridin-1-yl]- 2,8-bis(trifluoromethyl)quinolines
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Articles in the same Issue
- Inhalt
- Author Index of Volume 228 Issues 1–11
- Symmetry and the polar state of condensed molecular matter
- “Forbidden” reflections in neutron diffraction on bismuth metal oxides: symmetry reduction, λ/2 effect or Umweganregung?
- The keyite crystal structure, revisited
- Liebau density vector: a new approach to characterize lone electron pairs in mullite-type materials
- Magnesium and cadmium in covalently bonded networks: synthesis and structure of AETMg and AETCd (AE = Ca, Sr; T = Pd, Ag, Pt, Au) with TiNiSi type structure and the solid solution Yb2–xPtMgx
- Synthesis and structure of RE2RuMg2 (RE = Dy, Ho, Er, Tm, Lu) – i5 superstructures of the bcc packing
- Co4 clusters in the high-temperature phase La18Co28In3
- Crystal structures of mefloquine-oxazolidine derivatives, 4-[3-(halophenyl)hexahydro[1,3]oxazolo[3,4-a]pyridin-1-yl]- 2,8-bis(trifluoromethyl)quinolines
- X-ray crystal structures of specifically substituted and derived 4,4′-dihydroxybiphenyls. Influence of the structural modification
