Wan Lei, Wang Qingqing, Ye Xiaoqiu, Cao Xingzhong, Jin Shuoxue, Gao Tao
Institute of Atomic and Molecular Physics, Sichuan University Chengdu Sichuan 610065 P. R. China
Science and Technology on Surface Physics and Chemistry Laboratory Mianyang Sichuan 621907 P. R. China.
RSC Adv. 2020 Jan 20;10(6):3277-3292. doi: 10.1039/c9ra07314k. eCollection 2020 Jan 16.
We have performed the first-principles method to study the structural stability and helium diffusion behavior of Fe-Cr alloys. The calculated bulk modulus of 284.935 GPa in the non-magnetic (NM) state is in good agreement with others. We have obtained solid evidence that the alloy structures meet the mechanical stability criteria and lattice dynamics conditions in the anti-ferromagnetism (AFM) and non-magnetic (NM) states. Compared with bulk γ-Fe, a slightly larger Young's modulus indicates that the doping of Cr helps to enhance the stiffness of the material and the ability to resist the reversible deformation of shear stress, but the ductility decreased slightly. Our results revealed that the addition of interstitial He atom promotes the expansion and deformation of the lattice, and further enlarges the cell volume. The presence of Cr in the alloy structures promotes the migration of a single helium atom between octahedral interstitials, and at the same time, inhibits the diffusion of helium atoms between tetrahedral interstitials to a large extent, which seem to be trapped in tetrahedral interstitials and cannot escape. The electronic properties show that the alloy materials exhibit obvious metallicity, and the doping of Cr generates an impurity state at lower energy, which is mainly formed by the s, p of Fe and s, p shell electrons of Cr. The charge density difference graphs corroborate that there is bonding interactions between Fe and Cr atoms. Bader charge analysis shows that a stronger polar covalent bond is formed between Fe and Cr in the non-magnetic (NM) state than in the anti-ferromagnetism (AFM) state. Our results provide useful information for understanding the initial growth of helium bubbles in experiments.
我们采用第一性原理方法研究了Fe-Cr合金的结构稳定性和氦扩散行为。计算得到的非磁性（NM）状态下的体模量为284.935 GPa，与其他结果吻合良好。我们已获得确凿证据，表明合金结构在反铁磁性（AFM）和非磁性（NM）状态下满足力学稳定性标准和晶格动力学条件。与块状γ-Fe相比，稍大的杨氏模量表明Cr的掺杂有助于提高材料的刚度以及抵抗剪切应力可逆变形的能力，但延展性略有下降。我们的结果表明，间隙He原子的加入促进了晶格的膨胀和变形，并进一步增大了晶胞体积。合金结构中Cr的存在促进了单个氦原子在八面体间隙之间的迁移，同时在很大程度上抑制了氦原子在四面体间隙之间的扩散，这些氦原子似乎被困在四面体间隙中无法逸出。电子性质表明，合金材料表现出明显的金属性，Cr的掺杂在较低能量处产生杂质态，主要由Fe的s、p以及Cr的s、p壳层电子形成。电荷密度差图证实了Fe和Cr原子之间存在键合相互作用。Bader电荷分析表明，在非磁性（NM）状态下Fe和Cr之间形成的极性共价键比在反铁磁性（AFM）状态下更强。我们的结果为理解实验中氦泡的初始生长提供了有用信息。
