Origin of forbidden reflections in multiferroic Ba$_2$CoGe$_2$O$_7$ by neutron diffraction: Symmetry lowering or Renninger effect?
Origin of forbidden reflections in multiferroic Ba$_2$CoGe$_2$O$_7$ by neutron diffraction: Symmetry lowering or Renninger effect?
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中子衍射在多铁性 Ba$_2$CoGe$_2$O$_7$ 中禁止反射的起源：对称性降低或伦宁格效应？
DOI：
10.1107/s1600576716002405
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发表时间：
2015
期刊：
影响因子：
--
通讯作者：
V. Hutanu
中科院分区：
文献类型：
--
作者：
A. Sazonov;M. Meven;G. Roth;R. Georgii;I. K'ezsm'arki;V. Kocsis;V. Hutanu
对于对称性一致的理论描述的多铁性相的Ba$_2$CoGe$_2$O$_7$一个精确的知识，它的晶体结构是一个先决条件。在我们以前的同步辐射X射线衍射实验在室温下的多铁性Ba$_2$CoGe$_2$O$_7$，我们发现禁止的反射，有利于四方到正交对称性降低标题化合物。在这里，我们报告的结果，室温单晶衍射研究与热中子和冷中子区分真实的对称性降低和多重衍射（Renninger效应）。实验的多个衍射图案与模拟的比较排除了对称性降低。因此，选择基于四元空间群P\bar{4}2_1m$的结构模型来描述室温下的Ba 2CoGe 2 O 7对称性。给出了300 K下中子衍射的精确结构参数，并与以前的X射线衍射结果进行了比较。
For a symmetry consistent theoretical description of the multiferroic phase of Ba$_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 $P\bar{4}2_1m$ 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.