共查询到19条相似文献,搜索用时 156 毫秒
1.
考虑到晶体的离散点阵结构,滑移只能在原子之间进行,因此位错中心永远没有原子,位错中心附近分摊到每个原子的离散弹性能量处处有限。在刚性位错假定下,直接应用位错弹性理论解析结果,求出了晶体直奇异位错等效内切半径及其随位错中心位置的周期变化。对于简单四方晶体中奇异螺型位错,一级近似与Peierls模型结果巧合。计算了fcc和bcc两种晶系中各种位错的自能和等效位错内切半径,并初步考虑了各向异性弹性效应。结果表明:位错滑移面不是几何平面,bcc螺型位错滑移面类似于蜂巢结构。指出了用这种离散弹性方法进一步估算各种次级效应的可能。
关键词: 相似文献
2.
针对刃型位错的滑移运动, 构建包含外力场与晶格原子密度耦合作用的体系自由能密度函数, 建立剪切应变作用体系的晶体相场模型. 模拟了双相双晶体系的位错攀移和滑移运动, 计算了位错滑移的Peierls势垒和滑移速度. 结果表明: 施加较大的剪切应变率作用, 体系能量变化为单调光滑曲线, 位错以恒定速度做连续运动, 具有刚性运动特征; 剪切应变率较小时, 体系能量变化出现周期波动特征, 位错运动是处于低速不连续运动状态, 运动出现周期“颠簸”式滑移运动, 具有黏滞运动特征; 位错启动运动, 存在临界的势垒. 位错启动攀移运动的Peierls势垒要比启动滑移Peierls势垒大几倍. 位错攀移和滑移运动特征与实验结果相符合. 相似文献
3.
利用离散变分方法和DMol方法,研究了体心立方Fe中1/2[111](110)刃型位错上扭折及掺杂(N,O)体系的电子结构.能量(杂质偏聚能及格位能)计算结果表明,杂质元素N,O进入扭折芯区的偏聚趋势,这与位错扭折引起的晶格畸变有关.同时,在杂质元素周围有一些电荷聚集,导致扭折上电荷的不均匀分布,杂质原子得到电子,其周围Fe原子失去电子.由于N原子的2p轨道与近邻Fe原子的3d4s4p轨道之间杂化,使N原子与近邻Fe原子间有较强的相互作用,不利于扭折的迁移,使位错运动受阻,有利于材料强度的提高;而O与最近邻Fe原子之间的相互作用较弱.杂质-扭折复合体的局域效应明显影响体系的电子结构、能量及性能.
关键词:
电子结构
刃型位错
扭折
杂质元素 相似文献
4.
在经典力学框架内和Seeger方程基础上,讨论了应变超晶格界面附近的位错动力学行为,指出了系统的非线性共振将导致位错的运动与堆积,并可能造成超晶格的分层或断裂.首先,引入阻尼项,在小振幅近似下,把描述一般位错运动的Seeger方程化为了超晶格系统的广义Duffing方程.利用多尺度法分析了系统的主共振、超共振和子共振,并找到了系统出现这三类共振的临界条件.结果表明,系统的临界条件与它的物理参数有关,只需适当调节这些参数就可以原则上避免共振的出现,保证了超晶格材料的完整性和性能的稳定性.
关键词:
位错动力学
应变超晶格
共振
分岔 相似文献
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采用晶体相场法研究非对称倾侧亚晶界结构及其在应力作用下的微观运动机制.分别从温度、倾斜度角以及应力施加方向等方面对其结构及迁移过程进行分析和讨论.结果表明,非对称倾侧亚晶界由符号相同的一排刃型位错等距排列,部分出现由两个相互垂直排列的刃型位错构成的位错组;在应力作用下,非对称倾侧亚晶界迁移的微观机制包括位错的滑移和攀移、位错组分解、单个位错与位错组反应、单个位错分解以及位错湮灭;温度降低和倾斜度增大都会阻碍亚晶界的迁移过程;应力方向改变导致位错运动方向改变,从而改变晶界迁移形式. 相似文献
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8.
一种硅基金属狭缝表面等离子体波导的设计 总被引:1,自引:1,他引:0
设计了一种适用于光电子集成电路的表面等离子体波导结构.利用三维全矢量时域有限差分法对该波导结构进行了数值模拟,并分析了其在基模传输时的模式场分布与金属结构顶角的关系以及其能量限制性.研究了该波导结构在不同金属材料下的有效折射率和传播长度对芯层宽度的依赖关系,讨论了两个该波导结构之间的耦合长度、最大转移功率和彼此间的串扰.结果表明:光场被高度限制在芯层区域,在金属结构顶角为135°时,其能量限制因子更高;在金属材料确定的情况下,有效折射率随芯层宽度增大而减小,而传播长度增大;在芯层宽度一定的条件下,两个波导结构间的耦合长度随波导间距增大而增大,最大转移功率和串扰随波导间距增大而减小. 相似文献
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10.
《物理学报》2020,(14)
采用晶体相场法模拟纳米尺度下小角度非对称倾斜晶界结构和位错运动,从外应力作用下晶界位错运动位置变化和晶体体系自由能变化角度,分析取向角对小角度非对称倾斜晶界结构和晶界位错运动的影响规律.研究表明,不同取向角下组成小角度非对称倾斜晶界的位错对类型相同.随取向角增大晶界位错对增加,且晶界更易形成n1n2型和n4n5型位错对.外应力作用下,不同取向角晶界位错对初始运动状态均沿晶界进行攀移运动,随体系能量积累,取向角越大出现晶界位错对分解的个数越多,且均为n1n2型和n4n5型位错对发生分解反应.不同取向角下小角度非对称倾斜晶界体系自由能曲线都存在四个阶段,分别对应位错对攀移、位错对滑移及分解、位错对反应抵消形成单晶和体系吸收能量自由能上升过程.进一步对比发现随取向角增大,晶界湮没形成的单晶体系所需时间增加. 相似文献
11.
Using Foreman’s method, the core structure and Peierls stress of dislocations in bubble rafts have been investigated within
the framework of the modified Peierls-Nabarro (P-N) model in which the discrete lattice effect is taken into account. The
core width obtained from the modified P-N model is much wider than that from the P-N model owing to the discrete lattice effect.
It is found that the core width of dislocation increases with a decrease of the bubble radius. The elastic strain energy associated
with the discrete effect is considered while calculating the Peierls stress. The new expression of the Peierls stress obtained
in this paper is not explicitly dependent on the particular form of the restoring force law, which is only related to the
core structure parameter and can be used expediently to predict the Peierls stress of dislocations. The Peierls stress decreases
rapidly with the decrease of the bubble radius. 相似文献
12.
Core structure and Peierls stress of the 90° dislocation and the 60° dislocation in aluminum investigated by the fully discrete Peierls model 下载免费PDF全文
The core structure, Peierls stress and core energy, etc. are comprehensively investigated for the $90^\circ$ dislocation and the $60^\circ$ dislocation in metal aluminum using the fully discrete Peierls model, and in particular thermal effects are included for temperature range $0\leq T \leq 900$ K. For the $90^\circ$ dislocation, the core clearly dissociates into two partial dislocations with the separating distance $D\sim 12$ Å, and the Peierls stress is very small $\sigma_{\rm p}<1$ kPa. The nearly vanishing Peierls stress results from the large characteristic width and a small step length of the $90^\circ$ dislocation. The $60^\circ$ dislocation dissociates into $30^\circ$ and $90^\circ$ partial dislocations with the separating distance $D\sim 11$ Å. The Peierls stress of the $60^\circ$ dislocation grows up from $1$ MPa to $2$ MPa as the temperature increases from $0$ K to $900$ K. Temperature influence on the core structures is weak for both the $90^\circ$ dislocation and the $60^\circ$ dislocation. The core structures theoretically predicted at $T=0$ K are also confirmed by the first principle simulations. 相似文献
13.
H. L. Zhang 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,81(2):179-183
The dislocation width for shuffle 60° dislocation in semiconductors Si and Ge have been calculated by the improved P-N theory in which the discrete effect has been taken into account. Peierls barrier and stress have been evaluated with considering the contribution of strain energy. The discrete effect make dislocation width wider, and Peierls barrier and stress lower. The dislocation width of 60° dislocation in Si and Ge is respectively about 3.84 Å and 4.00 Å (~1b, b is the Burgers vector). In the case of 60° dislocation, after considering the contribution of strain energy, Peierls barrier and stress are increased. The Peierls barrier for 60° dislocation in Si and Ge is respectively about 15 meV/Å and 12–14 meV/Å, Peierls stress is about 3.8 meV/Å3 (0.6 GPa) and 2.7–3.3 meV/Å3 (0.4–0.5 GPa). The Peierls stress for Si agrees well with the numerical results and the critical stress at 0 K extrapolated from experimental data. Ge behaves similarly to Si. 相似文献
14.
On the core structure and mobility of the 〈100〉{010} and 〈100〉{01^-1} dislocations in B2 structure YAg and YCu 下载免费PDF全文
Dislocations are thought to be the principal mechanism of high ductility of the novel B2 structure intermetallic compounds YAg and YCu.In this paper,the edge dislocation core structures of two primary slip systems 〈100 〉{010} and 〈100 〉 {011} for YAg and YCu are presented theoretically within the lattice theory of dislocation.The governing dislocation equation is a nonlinear integro-differential equation and the variational method is applied to solve the equation.Peierls stresses for 〈100 〉 {010} and 〈100 〉 {011} slip systems are calculated taking into consideration the contribution of the elastic strain energy.The core width and Peierls stress of a typical transition-metal aluminide NiAl is also reported for the purpose of verification and comparison.The Peierls stress of NiAl obtained here is in agreement with numerical results,which verifies the correctness of the results obtained for YAg and YCu.Peierls stresses of the 〈100 〉 {011} slip system are smaller than those of〈100 〉 {010} for the same intermetallic compounds originating from the smaller unstable stacking fault energy.The obvious high unstable stacking fault energy of NiAl results in a larger Peierls stress than those of YAg and YCu although they have the same B2 structure.The results show that the core structure and Peierls stress depend monotonically on the unstable stacking fault energy. 相似文献
15.
An improvement of the Peierls equation has been made by including the lattice effects. By using the
non-trivially gluing mechanism for the simple cubic lattice, in which atoms interact with its first and second nearest neighbours through a central force, the dislocation equation has been derived
rigorously for the isotropic case. In the slowly varying approximation, the Peierls equation with the improvement by including the lattice effects has been obtained explicitly. The new equation can be used to substitute for the old one in theoretical investigations of dislocations. The major change of
the predicted dislocation structure is in the core region. The width of the dislocation given by using the new equation is about three times that given by the classical Peierls--Nabarro theory
for the simple cubic lattice. 相似文献
16.
The analysis of screw dislocation motion in a lattice is extended to crystals with a preferred slip direction and to force laws of the “dangling bond” type. The external strain required for uniform motion, or the corresponding Peierls stress depends critically on the shape of the interatomic potential. For particular combinations of velocity, crystal anisotropy, and force law, the external strain drops sharply—indicating some modes of dislocation motion that are almost loss-free. Although the relation between dynamic Peierls stress and dislocation width is not monotonie, it shows a general exponential decrease. 相似文献
17.
In the classical
Peierls--Nabarro (P-N) theory of dislocation,
there is a long-standing contradiction that the stable configuration
of dislocation has maximum energy rather than minimum energy. In
this paper, the dislocation energy is calculated rigorously in the
context of the full lattice theory. It is found that besides the
misfit energy considered in the classical P-N theory, there is an
extra elastic strain energy that is also associated with the
discreteness of lattice. The contradiction can be automatically
removed provided that the elastic strain energy associated with the
discreteness is taken into account. This elastic strain energy is
very important because its magnitude is larger than the misfit
energy, its sign is opposite to the misfit energy. Since the elastic
strain energy and misfit energy associated with discreteness cancel
each other, and the width of dislocation becomes wide in the lattice
theory, the Peierls energy, which measures the height of the
effective potential barrier, becomes much smaller than that given in
the classical P-N theory. The results calculated here agree with
experimental data. Furthermore, based on the results obtained, a
useful formula of the Peierls stress is proposed to fully include
the discreteness effects. 相似文献
18.
H.-L. Zhang S.-F. Wang R. Wang J. Jiao 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,73(4):489-493
The dislocation widths and Peierls stresses of glide dislocations and shuffle dislocations in graphene have been studied by
the improved Peierls-Nabarro (P-N) equation which contains the discrete correction. The discrete parameter is obtained from
a simple dynamic model in which the
interaction attributed to the variation of bond length and angle was considered. The restoring force in the improved P-N equation
is given by the gradient of the generalized stacking fault energy
surface (γ-surface). Our calculation shows that the widths of the shuffle dislocation and the glide dislocation are narrow
and the width of the shuffle dislocation is about twice wider than the glide dislocation. The Peierls stress of a shuffle
dislocation is one order of magnitude smaller than that of a glide dislocation. As a consequence, the shuffle dislocation
moves more easily than the glide dislocation. 相似文献
19.
In this study, the modified embedded-atom method (MEAM) was applied to compare the predictions of dislocation core properties obtained by molecular statics with the continuum predictions obtained in the framework of the simplified 1D-Peierls–Nabarro model. To this end, a set of four fictive Li potentials in the MEAM framework was proposed with the condition that all four potentials reproduce the same elastic constants, the same transition energies between bcc and fcc crystal structures, and between bcc and hcp crystal structures, while the unstable stacking fault energy on the plane {110} in the direction <111> was varied around the value predicted by first-principles. Within these potentials, direct atomistic calculations were performed to evaluate dislocation core properties such as dislocation half width and Peierls stress and the results were compared with continuum predictions. We found that the trends predicted by the Peierls–Nabarro model, i.e. (i) a decrease of the dislocation half width with increasing unstable stacking fault energy, and (ii) an increase of the Peierls stress with increasing the magnitude of the unstable stacking fault energy, were recovered using atomic calculations in the MEAM framework. Moreover, the magnitude of the dislocation half width and the Peierls stress calculated in the MEAM framework are in good agreement with the Peierls–Nabarro predictions when the dislocation half width is determined using a generic strategy. Specifically, the dislocation half width is defined as the distance for which the disregistery is included between b/4 and 3b/4. It was, therefore, demonstrated herein that the set of fictive potentials could be parameterized in the MEAM framework to validate or to disprove the continuum theory using atomistic methods. 相似文献