Radboud University Nijmegen, Institute for Molecules and Materials, Electronic Structure of Materials, Nijmegen, The Netherlands.
Phys Chem Chem Phys. 2011 Apr 7;13(13):6043-52. doi: 10.1039/c0cp01540g. Epub 2011 Feb 22.
The lithium amide (LiNH(2)) + lithium hydride (LiH) system is one of the most attractive light-weight materials options for hydrogen storage. Its dehydrogenation involves mass transport in the bulk (amide) crystal through lattice defects. We present a first-principles study of native point defects and dopants in LiNH(2) using density functional theory. We find that both Li-related defects (the positive interstitial Li(i)(+) and the negative vacancy V(Li)(-)) and H-related defects (H(i)(+) and V(H)(-)) are charged. Li-related defects are most abundant. Having diffusion barriers of 0.3-0.5 eV, they diffuse rapidly at moderate temperatures. V(H)(-) corresponds to the NH ion. It is the dominant species available for proton transport with a diffusion barrier of ∼0.7 eV. The equilibrium concentration of H(i)(+), which corresponds to the NH(3) molecule, is negligible in bulk LiNH(2). Dopants such as Ti and Sc do not affect the concentration of intrinsic defects, whereas Mg and Ca can alter it by a moderate amount. Ti and Mg are easily incorporated into the LiNH(2) lattice, which may affect the crystal morphology on the nano-scale.
氨基锂（LiNH(2)) + 氢化锂（LiH）系统是最有吸引力的几种轻质储氢材料选项之一。其脱氢过程涉及通过晶格缺陷在体相（酰胺）晶体中的质量传输。我们使用密度泛函理论对 LiNH(2)中的本征点缺陷和掺杂剂进行了第一性原理研究。我们发现，Li 相关的缺陷（正间隙 Li(i)(+)和负空位 V(Li)(-))和 H 相关的缺陷（H(i)(+)和 V(H)(-))都是带电的。Li 相关的缺陷最为丰富。其扩散势垒为 0.3-0.5 eV，在中等温度下迅速扩散。V(H)(-)对应于NH离子。它是质子传输的主要物种，扩散势垒约为 0.7 eV。对应于 NH(3)分子的 H(i)(+)的平衡浓度在体相 LiNH(2)中可以忽略不计。掺杂剂如 Ti 和 Sc 不会影响本征缺陷的浓度，而 Mg 和 Ca 可以适度改变其浓度。Ti 和 Mg 很容易掺入 LiNH(2)晶格中，这可能会影响纳米尺度上的晶体形态。
