paper

Origin of forbidden reflections in multiferroic Ba $_{2}$ CoGe $_{2}$ O $_{7}$ by neutron diffraction: Symmetry lowering or Renninger effect?

arXiv:1511.02783

Abstract

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 our previous synchrotron X-ray diffraction experiment on multiferroic Ba $_{2}$ CoGe $_{2}$ O $_{7}$ at room temperature we found forbidden reflections that favour the tetragonal-to-orthorhombic symmetry lowering of the titled compound. Here, we report the results of room-temperature single-crystal diffraction studies with both hot and cold neutrons to differentiate between the real symmetry lowering and multiple diffraction (the Renninger effect). A comparison of the experimental multiple diffraction patterns with simulated ones rules out the symmetry lowering. Thus, the structural model based on the tetragonal space group $P 4 ˉ 2_{1} m$ was selected to describe the Ba $_{2}$ CoGe $_{2}$ O $_{7}$ symmetry at room temperature. The precise structural parameters from neutron diffraction at 300K are presented and compared with the previous X-ray diffraction results.

5 pages, 3 figures, 3 tables, submitted for publication

Origin of forbidden reflections in multiferroic Ba2​CoGe2​O7​ by neutron diffraction: Symmetry lowering or Renninger effect?

Abstract

Origin of forbidden reflections in multiferroic Ba $_{2}$ CoGe $_{2}$ O $_{7}$ by neutron diffraction: Symmetry lowering or Renninger effect?