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本文采用重合位置点阵理论构建了α-Fe的Σ3[110](112)对称倾转晶界模型,通过基于密度泛函理论的平面波超软赝势方法研究了稀土La元素在α-Fe中的占位倾向.结果表明,La在α-Fe晶界的杂质形成能最低,因而La原子倾向于占据晶界区;掺杂La前后的α-Fe晶界电子结构计算结果显示,La占位于α-Fe晶界会使体系中的电荷发生重新分配,将提供更多电子用于晶界区成键,使得Fe原子得到更多的电子,这将导致掺杂区原子间结合有离子化趋势,从而使La与晶界区相邻Fe原子之间的相互作用加强,也使晶界原子与晶界两侧Fe原子的键合加强,从能量角度解释了材料宏观力学性能变化的原因;计算同时发现,La加入后,也使晶界上的原子成键区态密度左移,降低了体系的总能量,使晶界结构更为稳定.
In this paper, the Σ3 [110] (112) symmetric tilting grain boundary model of α-Fe was constructed by the coincidence position lattice theory. The effects of rare earth elements La on α-Fe were studied by plane wave super soft pseudopotential method based on density functional theory The results show that the formation energy of La is the lowest in the α-Fe grain boundary, and therefore the La atoms tend to occupy the grain boundary region. The calculations of the electronic structure of α-Fe before and after La doping show that La occupies the The α-Fe grain boundary redistributes charge in the system, providing more electrons for bonding at the grain boundaries, resulting in more electrons from the Fe atoms, which leads to a tendency to ionize between atoms in the doped regions So that the interaction between La and the neighboring Fe atoms in the grain boundary region is strengthened and the bonding between the grain boundary atoms and the Fe atoms on both sides of the grain boundary is strengthened and the reason for the change of macroscopic mechanical properties is explained from the energy point. It is also found that the addition of La also shifts the density of the atomic bonding states to the left of the grain boundary and reduces the total energy of the system, resulting in a more stable grain boundary structure.