Ab initio study of symmetrical tilt grain boundaries in bcc Fe: structural units, magnetic moments, interfacial bonding, local energy and local stress
Ab initio study of symmetrical tilt grain boundaries in bcc Fe: structural units, magnetic moments, interfacial bonding, local energy and local stress
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DOI：
10.1088/0953-8984/25/13/135004
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发表时间：
2013-04-03
影响因子：
2.7
通讯作者：
Kohyama, Masanori
中科院分区：
文献类型：
--
作者：
Bhattacharya, Somesh Kr;Tanaka, Shingo;Kohyama, Masanori
我们提出了第一性原理计算的对称倾斜晶界（GBs）的体心立方铁。利用密度泛函理论（DFT）研究了σ 3（111）和σ 11（332）GBs的结构、电学和磁学性质。优化的结构，GB能量和GB超额自由体积与以前的DFT和经典模拟研究是一致的。GB构型可以通过Nakashima和Takeuchi（2000 ISIJ 86 357）给出的结构单元模型来解释。这两种GBs都是由相似的三元环和五元环结构单元组成，但根据旋转角的不同，在界面处具有不同的密度。具有较大原子体积的界面原子显示出比体值更高的磁矩，而具有较短键长的界面原子在每个GB中具有降低的磁矩。电荷密度和局域态密度表明，短键长的界面键具有更强的共价性，其中少数自旋电子起主导作用，这是铁磁性Fe的典型性质。为了理解这些GB的结构稳定性，我们使用Shiihara等人（2010 B 81 075441）的方案计算了每个原子区域的局部能量和局部应力。在每个晶界中，具有较大原子体积和增强磁矩的界面原子显示出较大的局部能量增加和张应力。构成具有降低的磁矩的更多共价键的界面原子具有较低的局部能量增加，有助于稳定化，同时在这些原子处产生压应力。这两个GB之间的相对稳定性可以通过结构单元的局部能量来理解。局域能量和局域应力分析是基于价电子行为研究晶界结构特性的有力工具。
We present first-principle calculations on symmetric tilt grain boundaries (GBs) in bcc Fe. Using density functional theory (DFT), we studied the structural, electronic and magnetic properties of Sigma 3(111) and Sigma 11(332) GBs formed by rotation around the [110] axis. The optimized structures, GB energies and GB excess free volumes are consistent with previous DFT and classical simulation studies. The GB configurations can be interpreted by the structural unit model as given by Nakashima and Takeuchi (2000 ISIJ 86 357). Both the GBs are composed of similar structural units of three-and five-membered rings with different densities at the interface according to the rotation angle. The interface atoms with larger atomic volumes reveal higher magnetic moments than the bulk value, while the interface atoms with shorter bond lengths have reduced magnetic moments in each GB. The charge density and local density of states reveal that the interface bonds with short bond lengths have more covalent nature, where minority-spin electrons play a dominant role as the typical nature of ferromagnetic Fe. In order to understand the structural stability of these GBs, we calculated the local energy and local stress for each atomic region using the scheme of Shiihara et al (2010 Phys. Rev. B 81 075441). In each GB, the interface atoms with larger atomic volumes and enhanced magnetic moments reveal larger local energy increase and tensile stress. The interface atoms constituting more covalent-like bonds with reduced magnetic moments have lower local energy increase, contributing to the stabilization, while compressive stress is generated at these atoms. The relative stability between the two GBs can be understood by the local energies at the structural units. The local energy and local stress analysis is a powerful tool to investigate the structural properties of GBs based on the behavior of valence electrons.