First-principles study of the micro-arrangement of hydrogen atoms and electronic properties of LaNi₅H_x (x: 0.5–7)

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• 作者：Chuanyu Zhang ; Tao Gao ; Xinhua Qi ; Yunguang Zhang ; Lijuan Tang ; Jingjing Zhou ; Bo Chen
• 关键词：Crystal structure ; Density functional theory ; Intermetallic compounds ; Electronic structure
• 刊名：Physica B
• 出版年：2008
• 出版时间：1 July 2008
• 年：2008
• 卷：403
• 期：13-16
• 页码：2372-2382
• 全文大小：518 K

文摘

The micro-arrangement of hydrogen atoms and the electronic properties of hydrides LaNi₅H_x (0.5, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0) have been systematically investigated by means of the density functional theory using the full-potential linearized augmented plane wave (FLAPW) method with the generalized gradient approximation (GGA). The calculated results indicate that H atoms prefer to occupy the 12n site in the solid solution phase. For the β phase, once the first H atom locates in the basal plane (12n site), and because it is difficult for the second H atom to still locate in the 12n site, the second H atom would prefer to occupy the middle plane site (6m site). When the number of H atoms increases from 3 to 5, they would occupy the other 12n and 6m sites by turns. Furthermore, our optimized data indicate that the structures P3 and P63mc are the most favorable structures of LaNi₅H₆ and LaNi₅H₇, respectively. From the analysis of the densities of states and charge densities, it is found that H atoms make a stronger covalent bond with Ni atoms than La atoms in LaNi₅H_x alloy. With the increase of hydrogen atoms in the host alloy, the Fermi energy of this system gradually increases, but the metallic characters and stabilities of hydrides LaNi₅H_x become poorer gradually.