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Origin of forbidden reflections in multiferroic Ba 2 CoGe 2 O 7 by neutron diffraction: symmetry lowering or Renninger effect?
Author(s) -
Sazonov Andrew,
Meven Martin,
Roth Georg,
Georgii Robert,
Kézsmárki István,
Kocsis Vilmos,
Tokunaga Yusuke,
Taguchi Yasujiro,
Tokura Yoshinori,
Hutanu Vladimir
Publication year - 2016
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s1600576716002405
Subject(s) - neutron diffraction , tetragonal crystal system , diffraction , orthorhombic crystal system , crystallography , multiferroics , condensed matter physics , symmetry (geometry) , powder diffraction , materials science , physics , crystal structure , optics , chemistry , dielectric , ferroelectricity , quantum mechanics , geometry , mathematics
For a symmetry‐consistent theoretical description of the multiferroic phase of Ba 2 CoGe 2 O 7 a precise knowledge of its crystal structure is a prerequisite. In a previous synchrotron X‐ray diffraction experiment on multiferroic Ba 2 CoGe 2 O 7 at room temperature, forbidden reflections were found that favour the tetragonal‐to‐orthorhombic symmetry lowering of the compound [Hutanu, Sazonov, Murakawa, Tokura, Náfrádi & Chernyshov (2011), Phys. Rev. B , 84 , 212101]. Here, the results are reported of room‐temperature single‐crystal diffraction studies with both hot and cold neutrons to differentiate between genuine symmetry lowering and multiple diffraction (the Renninger effect). A comparison of the experimental multiple diffraction patterns with simulated ones rules out symmetry lowering. Thus, the structural model based on the tetragonal space group was selected to describe the Ba 2 CoGe 2 O 7 symmetry at room temperature. The precise structural parameters from neutron diffraction at 300 K are presented and compared with the previous X‐ray diffraction results.