Crystal Structure and Charge Density Analysis of Li2NH by Synchrotron X‐Ray Diffraction.
Crystal Structure and Charge Density Analysis of Li2NH by Synchrotron X‐Ray Diffraction.
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DOI：
10.1002/chin.200529004
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发表时间：
2005-05
期刊：
影响因子：
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通讯作者：
T. Noritake;H. Nozaki;M. Aoki;S. Towata;G. Kitahara;Y. Nakamori;S. Orimo
中科院分区：
文献类型：
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作者：
T. Noritake;H. Nozaki;M. Aoki;S. Towata;G. Kitahara;Y. Nakamori;S. Orimo
摘要LiNH2和Li2NH等复合氢化物是最有前途的可逆储氢材料之一。本文用同步辐射粉末X射线衍射法在室温下研究了Li2NH晶体中氢的成键性质。用Rietveld方法对晶体结构进行了细化，并用最大熵法(MEM)分析了其电荷密度分布。Li2NH晶体为反萤石型结构(空间群Fm3‘m)，由Li和NH组成。氢原子随机占据N原子周围的48h(Wyackoff记数)位置。精炼后的晶格常数为a=5.0742(2)A。Li2NH中NH阴离子周围的电荷密度分布几乎为球形。根据得到的电荷密度分布估计了Li和NH周围球体内的电子数。结果表明，离子电荷为[Li0.99+]2[NH]1.21−。因此，从实验上证实了Li2NH是以离子键合的。
Abstract Complex hydrides, such as lithium amide (LiNH2) and lithium imide (Li2NH), have recently been noticed as one of the most promising materials for reversible hydrogen storage. In this paper, we reveal the bonding nature of hydrogen in Li2NH crystal by synchrotron powder X-ray diffraction measurement at room temperature. The crystal structure was refined by Rietveld method and the charge density distribution was analyzed by maximum entropy method (MEM). The Li2NH crystal is anti-fluorite type structure (space group F m 3 ¯ m ) consisting of Li and NH. Hydrogen atom occupies randomly the 48h (Wyckoff notation) sites around N atom. The refined lattice constant is a = 5.0742(2) A. The charge density distribution around NH anion in Li2NH is almost spherical. The number of electrons within the sphere around the Li and NH is estimated from the obtained charge density distribution. As the result, the ionic charge is expressed as [Li0.99+]2[NH]1.21−. Therefore, it is confirmed experimentally that Li2NH is ionically bonded.