Cr在α-Fe(C)中对C扩散影响的第一性原理研究

First-principles of influence of Cr on C diffusion inα-Fe(C)

为了研究Cr原子加入α-Fe(C)中对C原子扩散的影响,基于自旋极化密度泛函理论的第一性原理方法,采用广义梯度近似(GGA)下的PBE泛函形式和攀升图像微扰弹性带(CI-NEB)方法,首先分析Cr原子和C原子在α-Fe中的占位;其次,通过体系的分波态密度图和bader电荷布局分析α-Fe(C)-Cr体系的电子结构;最后,计算在α-Fe(C)-Cr体系中C原子位于Cr原子不同近邻位置时的相互作用以及C原子在α-Fe(C)和α-Fe(C)-Cr这2种体系中的扩散激活能。研究结果表明:Cr原子在α-Fe中占据体心位置和顶角位置时晶胞体积变化率无明显差别,Cr原子在α-Fe中占位无明显偏向性;C原子在α-Fe中占据八面体位置;Cr在α-Fe内与C原子的键合作用较弱,与Fe原子的键合作用较强,增强了晶胞稳定性;在α-Fe(C)-Cr体系中,Cr和C之间相互排斥,随着距离增加其相互作用能越来越弱,并在距离超过1.75a_(α-Fe)时趋于0;Cr原子加入α-Fe(C)后,当C原子朝着远离Cr原子的方向扩散时,Cr原子与C原子之间的相互作用降低了其扩散激活能,且随着C-Cr间距离增加,扩散激活能逐渐趋于α-Fe(C)体系中C原子的扩散激活能。

To study the effect of adding Cr atom toα-Fe(C)on the diffusion of C atom,the generalized gradient approximation(GGA)of PBE functional form and climbing Image Perturbation Elastic Band(CI-NEB)method were employed based on the first-principles method of spin-polarized density functional theory.Firstly,the occupancy of Cr atom and C atom inα-Fe was analyzed.Secondly,the electronic structure ofα-Fe(C)-Cr system was analyzed by means of partial density of states and bader charge population.Finally,the interaction of Cr atom and C atom inα-Fe(C)-Cr system was calculated when C atom was located at different neighboring positions of Cr atom.The diffusion activation energy of C atom inα-Fe(C)andα-Fe(C)-Cr systems was calculated.The results show that there is no significant difference in the cell volume change rate when Cr atom occupies body center position and vertex angle position inα-Fe,and there is no obvious preference for the occupying position of Cr atom inα-Fe.C atom occupies octahedral position inα-Fe.Cr atom has a weak bond with C atom inα-Fe,and a strong bond with Fe atoms,which enhances the stability of the unit cell.Inα-Fe(C)-Cr system,Cr atom and C atom repel each other,the interaction energy becomes weaker as the distance increases,and tends to 0 when the distance exceeds about 1.75a_(α-Fe).After Cr atom is added toα-Fe(C),C atom diffuses away from Cr atom and the interaction between Cr atom and C atom reduces their diffusion activation energy.The diffusion activation energy approaches that of C atom inα-Fe(C)system with the increase of distance between C and Cr.