Strain-field effects on the formation and migration energies of self interstitials in α-Fe from first principles
Strain-field effects on the formation and migration energies of self interstitials in α-Fe from first principles
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DOI：
10.1103/physrevb.81.094102
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发表时间：
2010-03-01
影响因子：
3.7
通讯作者：
Seif, Dariush
中科院分区：
文献类型：
--
作者：
Chen, Zhengzheng;Kioussis, Nicholas;Seif, Dariush
采用从头算方法研究了α - fe中单自间隙原子（SIA）在外部变形作用下的稳定性和迁移率。从头算结果表明，与连续介质弹性理论的线性行为相反，SIA地层能量在膨胀和压缩状态下的体积和单轴应变依赖关系是不同的。我们发现了一个< 111 >-> < 100 >的SIA定向机制，该机制是由< 11x >垂直杆（x=2.7）结构引起的单轴膨胀引起的。体积变形和单轴变形对< 110 >{110}< 100 >{100}相变和< 111 >< 100 >重定向的运移路径和活化能垒也有相当大的影响。结果表明：(1)体积膨胀（压缩）显著降低（增加）迁移能垒，使扩散过程三维化；(2)单轴应变消除（降低）< 111 >->< 11x >竖条（x=2.7）（< 11x >竖条(x=2.7)->< 100 >）相变的迁移能垒，导致< 111 > SIA自发重定向；(3)单轴变形破坏了体系的立方对称，从而导致了不同方向上迁移速率的各向异性。这些计算表明，由整体弹性变形引起的电子结构的变化对形成和迁移能有额外的贡献，这既不能用弹性理论也不能用经验原子间势来充分解释。
Ab initio electronic structure calculations are employed to study the stability and mobility of mono-self interstitial atoms (SIA) in alpha-Fe under external deformation. The ab initio results indicate that the volumetric and uniaxial strain dependences of the SIA formation energy are different in the expansion and compression regimes, in contrast to the linear behavior in continuum elasticity theory. We find a < 111 >-> < 100 > SIA reorientation mechanism induced by uniaxial expansion which proceeds via < 11x >vertical bar(x=2.7) configuration. Volumetric and uniaxial deformations are also found to have a considerable influence on the migration paths and activation energy barriers for the < 110 >{110}< 100 >{100} transformation and the < 111 >< 100 > reorientation. The results reveal that (i) the volumetric expansion (compression) decreases (increases) substantially the migration energy barrier and renders the diffusion process three (one) dimensional, (ii) the uniaxial strain removes (decreases) the migration energy barrier for the < 111 >->< 11x >vertical bar(x=2.7)(< 11x >vertical bar(x=2.7)->< 100 >) transformation, leading to spontaneous reorientation of the < 111 > SIA, and (iii) the uniaxial deformation breaks the cubic symmetry of the system and in turn induces anisotropy of the migration rates along different directions. These calculations demonstrate that changes in the electronic structure induced by global elastic deformation lead to additional contributions to the formation and migration energies, which cannot be adequately accounted for neither by elasticity theory nor by empirical interatomic potentials.