Structural Insights into the Lithium Amide-Imide Solid Solution
Structural Insights into the Lithium Amide-Imide Solid Solution
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DOI：
10.1021/acs.jpcc.7b02441
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发表时间：
2017-06-08
影响因子：
3.7
通讯作者：
David, William I. F.
中科院分区：
文献类型：
--
作者：
Makepeace, Joshua W.;David, William I. F.
氨基化锂（LiNH 2）和亚胺化锂（Li 2NH）的固溶体在通过亚胺化锂的氨分解催化和氢储存和释放反应期间存在于氨基化锂氢化锂复合物中。因此，它们是促进氢作为可持续能源储存的重要材料。为了理解这些溶液的性质，合成了一系列跨越氨基锂和亚胺锂之间的固溶体的全化学计量范围的样品。粉末衍射测量表明，在所有的样品中观察到的非化学计量的立方相的高温相的亚胺锂同构。在接近氨基化锂的平均化学计量值中，观察到固溶体的不完全形成，除了立方非化学计量相之外还观察到四氨基化锂。在中子衍射数据的分析中，使用氮原子周围散射密度的“高尔夫球”来模拟结构中的可变化学计量。该分析揭示了与酰亚胺锂相比，非化学计量样品中氢分布的更大程度的无序。拉曼光谱表明，在化学计量和非化学计量的环境中的酰胺和酰亚胺基团可以区分的频率的N-H伸缩，与不同的频带观察到的酰胺和酰亚胺的N-H伸缩在两种环境中。
Solid solutions of lithium amide (LiNH2) and lithium imide (Li2NH) are present during ammonia decomposition catalysis by lithium imide and hydrogen storage and release reactions in the lithium amide lithium hydride composite. As such, they are important materials in facilitating the use of hydrogen as a sustainable energy store. In order to understand the properties of these solutions, a series of samples spanning the full stoichiometry range of the solid solution between lithium amide and lithium imide were synthesized. Powder diffraction measurements showed that a nonstoichiometric cubic phase isostructural to the high temperature phase of lithium imide was observed in all of the samples. In average stoichiometry values close to lithium amide, incomplete formation of a solid solution was observed, with tetragonal lithium amide observed in addition to the cubic nonstoichiometric phase. In analysis of neutron diffraction data, the variable stoichiometry in the structure was modeled using a "golf-ball" of scattering density around the nitrogen atom. This analysis revealed a greater degree of disorder in hydrogen distribution in the nonstoichiometric samples compared with lithium imide. Raman spectroscopy indicated that amide and imide groups in stoichiometric and nonstoichiometric environments can be differentiated by the frequency of the N-H stretch, with distinct bands observed for both amide and imide N-H stretches in both environments.