LiAlH<sub>4</sub>晶体结构及稳定性的第一性原理研究

张艺龙; 崔慢爱; 刘艳辉

doi:10.11858/gywlxb.20170561

Crystal Structure and Stability of LiAlH₄ from First Principles

doi: 10.11858/gywlxb.20170561

ZHANG Yilong,
CUI Man'ai^{*
, ,},
LIU Yanhui^{*
, ,}

Department of Physics, College of Science, Yanbian University, Yanji 133002, China

Funds:

National Natural Science Foundation of China 11764043

More Information

Author Bio:
ZHANG Yilong(1998—), male, undergraduate, major in computational physics under high pressure.E-mail:122696148@qq.com

Corresponding authors: CUI Man'ai(1979—), female, master, lecturer, major in computational physics under high pressure.E-mail:macui@ybu.edu.cn; LIU Yanhui(1971—), female, Ph.D, professor, major in computational physics under high pressure.E-mail:yhliu@ybu.edu.cn

摘要

摘要: 基于密度泛函理论的第一性原理赝势平面波方法，研究高压下三元碱金属氢化物LiAlH₄的相变行为，分析了LiAlH₄高压相变的物理机制。研究表明，在1.6 GPa时LiAlH₄发生了相变，从α-LiAlH₄转变为空间群为I2/b的β-LiAlH₄，相变时伴随18%的体积坍塌，即一级相变。通过分析声子色散曲线得出，相变与声子软化有关。Millikan布局分析表明，常压相(α-LiAlH₄)是很有潜力的储氢材料。
- 晶体结构储氢材料 /
- 密度泛函理论 /
- 压力诱导结构转变 /
- 电子结构 /
Abstract: The structural stability of LiAlH₄, a promising hydrogen storage material, under high pressure was researched using the ab initio pseudopotential plane wave method.It is found that the phase transition occurs at 1.6 GPa from the α-LiAlH₄ phase to the β-LiAlH₄ (space group I2/b) phase.This phase transition is identified as first-order in nature with volume contractions of 18%.Moreover, the analysis of the phonon dispersion curves suggests that phase transition is related to the phonon softening.Mulliken population analyses indicated that the ambient phase (α-LiAlH₄) is expected to be the most promising candidate for hydrogen storage.
- crystal structure /
- hydrogen storage materials /
- density functional theory /
- pressure-induced structural transition /
- electronic structure

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Figure 1. Volume vs. pressure curves of α-LiAlH₄ and β-LiAlH₄ phases (Enthalpy difference (per formula unit) between α-LiAlH₄ and β-LiAlH₄ as a function of pressure is shown in the insert.)

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Figure 2. Phonon dispersion relations and density of state in high-symmetry directions for the α-LiAlH₄ structure at 0 and 1.6 GPa

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Figure 3. Calculated total and partial electronic densities of states for α-LiAlH₄ structure at 0 GPa (a) and β-LiAlH₄ structure at 1.6 GPa (b) respectively

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Table 1. Optimized structural parameters, atomic position parameters for the α-LiAlH₄ and the β-LiAlH₄ structures

Phase	Unit-cell dimensions	Atom coordinates
α-LiAlH₄ (P2₁/c)	a=0.485 1 nm(0.481 7 nm^) b=0.781 4 nm(0.780 2 nm^) c=0.773 2 nm(0.782 1 nm^*)	Li:(0.585, 0.459, 0.829), (0.560, 0.466, 0.827)^* Al:(0.159, 0.204, 0.938), (0.139, 0.203, 0.930)^* H1:(0.193, 0.102, 0.766), (0.183, 0.096, 0.763)^* H2:(0.377, 0.371, 0.986), (0.352, 0.371, 0.975)^* H3:(0.254, 0.082, 0.119), (0.243, 0.081, 0.115)^* H4:(0.822, 0.268, 0.882), (0.799, 0.247, 0.872)^*
β-LiAlH₄ (I2/b)	a=0.445 2 nm b=0.445 9 nm c=1.010 2 nm β=89.978°	Li:(0, 0.250, 0.125) Al:(0, 0.250, 0.625) H1:(0.259, 0.425, 0.542) H2:(0.324, 0.508, 0.792)
Note:"*" represents experimental data from Ref.[18].

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Table 2. Average net charges, bond length (L) and scaled bond overlap population (P^s) between H, Al, and Li atoms in the α-LiAlH₄ (at 0 GPa) and the β-LiAlH₄ (at 2.0 GPa) structures

Phase	Average net charge			L/nm		P^s
Phase	H	Al	Li	Al─H	Li─H	Al─H	Li─H
α-LiAlH₄	-0.48	0.64	1.29	0.161 5	0.188 6	0.506	0.019
β-LiAlH₄	-0.46	0.55	1.28	0.162 8	0.206 7	0.534	-0.063

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