Department of Materials Science, Fudan University, Shanghai, China 200433.
Phys Chem Chem Phys. 2013 Jan 21;15(3):893-900. doi: 10.1039/c2cp43016a.
First-principles calculations based on density functional theory were carried out to investigate the formation and migration of native defects in LiNH(2)BH(3). The structural properties and formation energies of H, Li, N and B related defects in various charge states were examined. Our analysis showed that the dominant atomic H defects are positively and negatively charged H interstitial (I(H)(+) and I(H)(-)). The Li related defects are dominated by positively charged Li interstitial (I(Li)(+)) and negatively charged Li vacancy (V(Li)(-)). For N related defects, the energetically favorable defects are positively and negatively charged NH(2) interstitial (I(NH2)(+) and I(NH2)(-)), while B related defect is dominated by neutral BH(3) interstitial (I(BH3)(0)). Further results indicated that the neutral H(2) interstitial (I(H2)) has the lowest formation energy (0.31 eV), suggesting that the major defect in LiNH(2)BH(3) is I(H2). Investigation of migration processes of the defects showed that the migration barriers for V((B)H)(+) (positively charged H vacancy on a B-H site), I(H)(+) and I(H)(-) are relatively high (0.50-0.68 eV), whereas moderate diffusion barriers are presented for V((N)H)(-) (negatively charged H vacancy on a N-H site) and I(Li)(+) (0.29 and 0.32 eV, respectively). The V(Li)(-) and I(H2) defects can migrate with low energy barriers of 0.13 and 0.16 eV, respectively. With a low activation energy of 0.47 eV, I(H2) is the major diffusive species in LiNH(2)BH(3). Our calculation results further suggest that the creation of the V((N)H)(-), I(Li)(+) and V(Li)(-) defects is the rate-limiting step for their transportation in LiNH(2)BH(3).
基于密度泛函理论的第一性原理计算研究了 LiNH(2)BH(3)中本征缺陷的形成和迁移。我们考察了各种电荷态下 H、Li、N 和 B 相关缺陷的结构性质和形成能。分析表明，主要的原子 H 缺陷是带正电和带负电的 H 间隙（I(H)(+) 和 I(H)(-))。Li 相关缺陷主要由带正电的 Li 间隙（I(Li)(+)）和带负电的 Li 空位（V(Li)(-))组成。对于 N 相关缺陷，有利的缺陷是带正电和带负电的 NH(2)间隙（I(NH2)(+) 和 I(NH2)(-))，而 B 相关缺陷主要由中性 BH(3)间隙（I(BH3)(0))组成。进一步的结果表明，中性 H(2)间隙（I(H2)）具有最低的形成能（0.31 eV），表明 LiNH(2)BH(3)中的主要缺陷是 I(H2)。对缺陷迁移过程的研究表明，带正电的 H 空位（B-H 位上的正电荷 H 空位）V((B)H)(+)、I(H)(+)和 I(H)(-)的迁移势垒较高（0.50-0.68 eV），而带负电的 H 空位（N-H 位上的负电荷 H 空位）V((N)H)(-)和 I(Li)(+)的扩散势垒适中（分别为 0.29 和 0.32 eV）。V(Li)(-)和 I(H2)缺陷的迁移能垒较低，分别为 0.13 和 0.16 eV。I(H2)的迁移激活能低至 0.16 eV，为 0.47 eV，是 LiNH(2)BH(3)中主要的扩散物种。我们的计算结果进一步表明，V((N)H)(-)、I(Li)(+)和 V(Li)(-)缺陷的形成是它们在 LiNH(2)BH(3)中迁移的速率限制步骤。
