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The importance of proper crystal-chemical and geometrical reasoning demonstrated using layered single and double hydroxides

机译:使用分层的单和双氢氧化物证明了适当的晶体化学和几何推理的重要性

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摘要

Atomistic modelling techniques and Rietveld refinement of X-ray powder diffraction data are widely used but often result in crystal structures that are not realistic, presumably because the authors neglect to check the crystal-chemical plausibility of their structure. The purpose of this paper is to reinforce the importance and utility of proper crystal-chemical and geometrical reasoning in structural studies. It is achieved by using such reasoning to generate new yet fundamental information about layered double hydroxides (LDH), a large, much-studied family of compounds. LDH phases are derived from layered single hydroxides by the substitution of a fraction (x) of the divalent cations by trivalent. Equations are derived that enable calculation of x from the a parameter of the unit cell and vice versa, which can be expected to be of widespread utility as a sanity test for extant and future structure determinations and computer simulation studies. The phase at x = 0 is shown to be an α form of divalent metal hydroxide rather than the β polymorph. Crystal-chemically sensible model structures are provided for β-Zn(OH) and Ni- and Mg-based carbonate LDH phases that have any trivalent cation and any value of x, including x = 0 [i.e. for α-M(OH)mHO phases]. © 2013 International Union of Crystallography Printed in Singapore - all rights reserved.
机译:原子建模技术和X射线粉末衍射数据的Rietveld改进已被广泛使用,但通常会导致晶体结构不现实,这可能是因为作者忽略了检查其结构的晶体化学合理性。本文的目的是加强结构研究中适当的晶体化学和几何推理的重要性和实用性。通过使用这种推理来生成有关层状双氢氧化物(LDH)的新的基本信息,LDH是一个经过广泛研究的大型化合物家族。通过将二价阳离子的一部分(x)替换为三价,LDH相由层状单一氢氧化物衍生而来。得出了能够根据单位晶胞的a参数进行x的计算的方程,反之亦然,可以预期这些方程作为用于现有和未来结构确定以及计算机仿真研究的健全性测试具有广泛的用途。在x = 0处的相显示为二价金属氢氧化物的α形式而不是β多晶型物。为具有任何三价阳离子和任何x值(包括x = 0,即x = 0)的β-Zn(OH)以及基于Ni和Mg的碳酸盐LDH相提供了晶体化学敏感的模型结构。 (对于α-M(OH)mHO相)。 ©2013国际晶体学联盟,新加坡印刷-保留所有权利。

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    Richardson, IG;

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