| The microstructures of hydrogen storage materials including LaNi5-xAlx (x=0,0.25,0.75), LaNi5D0.3, LaNi4.75Al0.25D(x=1.6,1.91) were studied by neutron diffraction in this paper. The data of lattice constants, volumes of unit cells, phase's analysis, and positions of atoms in the unit cells in the materials were obtained by this method. In addition, the percentages of deuterium atoms in the samples after deuterium absorption were characterized. Based on the experimental data, the theoretical model of unit cells in the materials were established respectively by Material Studio software. Based on the first principle of density functional theory, energies, densities of states (DOS), neutron diffraction Power spectrums of the materials were simulated and calculated by Castep and Reflex modules in Material Studio software. The relationship between the structures and the properties of the materials were discussed.Refined results of neutron diffraction experiments showed that along with the increase of deuterium in the samples, the tetrahedron and octahedron positions were preempted in their unit cells. In LaNi5D0.3 unit cells, the 12n positions were preempted, different from which, the 6m and 12n positions in LaNi4.75Al0.25 and LaNi4.75Al0.25D1.91 were preempted by deuterium atioms. It was found that the positions which deuterium taken may not be the largest clearances in the unit cells. Besides the geometry factors, many other factors may induce the preemption. The volumes of the unit cells expanded when absorbed deuterium. The vloumes increase along with the amount of absorbed deuterium before the saturation. When the Ni atoms in the samples were partly displaced by Al atoms, the crystal lattice parameters will change to a certain extent because of their difference in atom dimension. So the crystal lattice should be change and the speed of absorb hydrogen.The theoretical calculation results of LaNi5D0.3 showed that the convergence of energy state diagram can only be obtained when the deuterium atoms were in 12n posotions. It indicates the deuterium atoms may only take the positions of 12n. This result accords to the experimental data. The theory calculation of LaNi4.25Al0.75 indicates that the Al atom has precedence when it comes into the unit cell. So we can reckon it sholbe take the position of flank of crystal.We have calculated and optimized the crystal lattice of LaNi5, and it was found that the result is close to the theoretical value.The calculation of model in which Ni atoms at 3g and 2c positions were replaced by Al atoms has been made. It was found that the 3g position is the most probable replacing position when the replacement of Al to Ni atoms taking place by comparing differences of lattic constant and energy. In additional there is two phase in LaNi4.25Al0.75D1.6 and LaNi4.25Al0.75D1.91. It isαphase andβphase.Comparing the bond structure and density of state, the deuterium atoms absorbed in LaNi5, LaNi5D0.3 and LaNi4Al is found to be with more activeity. This indicates an increase of electron number near the Fermi Energy in the compound after adsorbed deuterium and Al atom. Unit cell structure models of the materials were established by experimental data, and the experimental condition of neutron diffraction is simulated by Reflex module. The result of LaNi5 was calculated and the corresponding neutron diffraction spectrums were presented. Compared with the experimental neutron diffraction spectrums, the simulation data accorded with the experimental data in peak position and peak profile.
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