Withers R L, Aroyo M I, Perez-Mato J M, Orobengoa D
Research School of Chemistry, ANU, Canberra ACT 0200, Australia.
Acta Crystallogr B. 2010 Jun;66(Pt 3):315-22. doi: 10.1107/S0108768110009031. Epub 2010 May 6.
Structured diffuse-scattering intensities, whether of compositional or of pure displacive origin, static or dynamic, contain important information about the symmetry of the individual compositional and/or displacive modes responsible for the observed intensities. However, the interpretation of the experimental data is very often impeded by the lack of a symmetry-based approach to the analysis of the structured diffuse-scattering distributions. Recently, we have demonstrated the existence of systematic phonon selection rules for diffuse scattering that depend on the symmetries of the mode and the scattering vector, and not on the specific structure. Here, we show that such symmetry analysis can be successfully extended and also applied to structure-dependent diffuse scattering associated with 'disordered' materials: the combination of theoretically determined, diffuse-scattering extinction conditions with the concept of non-characteristic orbits proves to be very useful in the interpretation of the observed diffuse-scattering extinctions. The utility of this approach is illustrated by the analysis of diffuse-scattering data from ThAsSe, FeOF and FeF(2). The essential part of the associated calculations are performed by the computer programs NEUTRON (systematic phonon extinction rules in inelastic scattering) and NONCHAR (non-characteristic orbits of space groups) that are available on the Bilbao crystallographic server (http://www.cryst.ehu.es).
结构化漫散射强度，无论是成分性的还是纯位移性的，静态的还是动态的，都包含有关导致观测强度的各个成分和/或位移模式对称性的重要信息。然而，实验数据的解释常常因缺乏基于对称性的结构化漫散射分布分析方法而受阻。最近，我们已经证明了存在依赖于模式和散射矢量对称性而非特定结构的漫散射系统声子选择规则。在此，我们表明这种对称性分析可以成功扩展并应用于与“无序”材料相关的结构依赖型漫散射：理论确定的漫散射消光条件与非特征轨道概念的结合在解释观测到的漫散射消光时被证明非常有用。通过对ThAsSe、FeOF和FeF₂的漫散射数据进行分析，说明了这种方法的实用性。相关计算的关键部分由可在毕尔巴鄂晶体学服务器（http://www.cryst.ehu.es）上获取的计算机程序NEUTRON（非弹性散射中的系统声子消光规则）和NONCHAR（空间群的非特征轨道）执行。
