Averaging the intensity of many-layered structures for accurate stacking-fault analysis using Rietveld refinement
Averaging the intensity of many-layered structures for accurate stacking-fault analysis using Rietveld refinement
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DOI：
10.1107/s1600576716013066
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发表时间：
2016-10-01
影响因子：
6.1
通讯作者：
Lewis, James W.
中科院分区：
文献类型：
--
作者：
Coelho, Alan A.;Evans, John S. O.;Lewis, James W.
许多技术上重要的合成和天然材料显示堆垛层错，这导致其粉末衍射图案中复杂的峰加宽、不对称和移位。可以使用包含层的明确描述的放大的单位晶胞（称为超晶胞）来描述图案。由于超级原胞可以包含数十万个原子，具有数十万个hkl反射，因此Rietveld方法对于除了最简单的系统之外的所有系统都要求太高的计算。本文介绍了在计算机程序TOPAS第6版（Bruker AXS，Karlsruhe，德国）中实现Rietveld精化所必需的加速。实施的技术包括：峰值缓冲器，其允许由几百个峰值自动地近似几十万个依赖于HKL的峰值形状;对计算时间具有最小影响的几百个大超级单元的平均过程;平滑技术，其允许使用近似10到20倍大的超级单元的小超级单元;以及用于堆叠序列生成的有效算法。其结果是Rietveld细化的超级细胞运行速度比传统Rietveld细化快几千倍。这允许在复杂的堆垛层错样品的结构和微观结构的定量和同时分析。
Many technologically important synthetic and natural materials display stacking faults which lead to complex peak broadenings, asymmetries and shifts in their powder diffraction patterns. The patterns can be described using an enlarged unit cell (called a supercell) containing an explicit description of the layers. Since the supercell can contain hundreds of thousands of atoms with hundreds of thousands of hkl reflections, a Rietveld approach has been too computationally demanding for all but the simplest systems. This article describes the implementation of the speed-ups necessary to allow Rietveld refinement in the computer program TOPAS Version 6 (Bruker AXS, Karlsruhe, Germany). Techniques implemented include: a peaks buffer that allows hundreds of thousands of hkl-dependent peak shapes to be automatically approximated by a few hundred peaks; an averaging process for hundreds of large supercells with minimum impact on computational time; a smoothing technique that allows for the use of small supercells which approximate supercells ten to 20 times larger; and efficient algorithms for stacking sequence generation. The result is Rietveld refinement of supercells operating at speeds several thousand times faster than traditional Rietveld refinements. This allows quantitative and simultaneous analysis of structure and microstructure in complex stacking-faulted samples.