金属钛中氦团簇融合的分子动力学模拟

运用分子动力学方法研究了金属钛中氦的扩散聚集行为.在300—800K的温度范围内,模拟了钛基底中氦团簇之间的融合过程.研究发现,温度的升高会加快氦团簇的融合.在300—800K,融合后的氦团簇在所模拟的时间尺度内三维结构保持不变.模拟结果还表明,常温下氦团簇之间的吸引力是导致氦团簇融合的重要因素. 关键词： 氦团簇 团簇融合 分子动力学模拟     

bcc Fe的刃型位错中氦-空位团的稳定性

 采用周期性原子阵列方法建立bcc Fe中的刃型位错,利用分子动力学计算了0 K时bcc Fe的位错芯里氦-空位团的稳定性,并与理想Fe晶体里氦-空位团的稳定性进行比较发现,位错的作用导致氦-空位团不稳定。点缺陷（He、空位与自间隙Fe原子）与氦-空位团的结合能与团中氦-空位比例密切相关,当氦与空位数之比在3~6时,结合能趋于稳定。     

金属钛中氦团簇生长行为的分子动力学研究

运用分子动力学方法模拟了常温下金属钛中氦团簇的生长过程.从能量的角度考察了氦团簇的生长机理.研究发现,随着氦团簇的生长,在氦团簇周围逐渐形成位错环缺陷,氦团簇与氦原子的结合能有逐渐下降的趋势,当氦团簇生长到一定尺寸时会通过发射周围缺陷以使得结合能上升,从而增强了进一步吸收氦原子的能力.模拟还发现,随着氦团簇的继续生长,氦团簇的形状由原来的不规则结构逐渐变成了较为规则的棱柱形结构,在随后的生长过程中其生长仅在（001）平面进行,沿［001］轴的厚度几乎不变. 关键词： 氦团簇 缺陷发射 分子动力学模拟     

铜原子纳米团簇热力学性质的分子动力学模拟研究

本文利用分子动力学模拟方法，研究了CuN（N=80、140、216、312、408、500、628和736）纳米团簇在热化和冷凝过程中结构和热力学性质的变化，模型采用的是Johnson的EAM作用势．模拟结果表明：铜团簇的熔点和凝固。点随其尺寸线性增加，并逐渐向大块晶体靠拢；所有团簇的凝固。羔都低于熔点，出现凝固过程中的滞后现象；在熔点和凝固点附近，团簇都具有负热容特性，负热容是由相变前后团簇内部结构突变引起的。     

铜原子纳米团簇热力学性质的分子动力学模拟研究

本文利用分子动力学模拟方法,研究了CuN(N=80、140、216、312、408、500、628和736)纳米团簇在热化和冷凝过程中结构和热力学性质的变化,模型采用的是Johnson的EAM作用势.模拟结果表明:铜团簇的熔点和凝固点随其尺寸线性增加,并逐渐向大块晶体靠拢;所有团簇的凝固点都低于熔点,出现凝固过程中的滞后现象;在熔点和凝固点附近,团簇都具有负热容特性,负热容是由相变前后团簇内部结构突变引起的.     

铜原子纳米团簇热力学性质的分子动力学模拟研究

利用分子动力学模拟方法,研究了CuN(N=80,140,216,312,408,500,628和736)纳米团簇在热化和冷凝过程中结构和热力学性质的变化,模型采用的是Johnson的EAM作用势.模拟结果表明:铜团簇的熔点和凝固点随其尺寸线性增加,并逐渐向大块晶体靠拢;所有团簇的凝固点都低于熔点,出现凝固过程中的滞后现象;在熔点和凝固点附近,团簇都具有负热容特性,负热容是由相变前后团簇内部结构突变引起的.     

金属钨中氦行为的分子动力学模拟

采用分子动力学方法模拟了氦在金属钨中的扩散聚集行为. 首先,建立了氦与钨原子间相互作用势,短程部分采用ZBL势形式,长程部分采用从头算法数据,实现了两者之间的平滑连接. 通过计算氦在钨中不同间隙位的形成能发现,单个氦原子更易存在于金属钨中的四面体间隙位,这与最新的研究成果是一致的. 在400-1200 K的温度范围内,考察了氦原子在金属钨中的扩散行为,获得了扩散迁移能,其值介于实验值和从头算法结果之间. 最后,研究了氦的聚集行为,从能量的角度考察了氦团簇形成初期的生长机理. 研究发现,在氦团簇形成初期,氦团簇对氦的结合能随着氦团簇的生长有逐渐增大的趋势,说明氦团簇吸收氦的能力逐渐增强. 关键词： 氦扩散 氦团簇 辐照损伤 分子动力学模拟     

金原子纳米团簇的负热容现象的分子动力学模拟研究

文中采用微正则分子动力学方法模拟研究了原子数N=60到675之间的6种金原子纳米团簇从固态到液态的熔解过程,得到了势能和热容量随温度的变化关系.其结果表明,所模拟的6种团簇在熔点附近出现负热容,通过对这些团簇熔解前后的势能以及结构变化的分析,探讨了产生负热容的微观机制.     

银、钴和铂原子纳米团簇熔化过程的分子动力学模拟

本采用分子动力学模拟方法，研究了银、钴和铂原子纳米团簇的熔化过程，模型采用的是Johson的EAM作用势。模拟结果表明，较大原子数目的纳米团簇其熔点随尺寸单调增加，而较小原子数目的团簇熔点和尺寸呈现无规则变化；大多数团簇在熔点附近都出现了负热容现象，说明负热容是纳米团簇在熔化过程中的一个普遍现象。     

银、钴和铂原子纳米团簇熔化过程的分子动力学模拟

本文采用分子动力学模拟方法,研究了银、钴和铂原子纳米团簇的熔化过程,模型采用的是Johson的EAM作用势.模拟结果表明,较大原子数目的纳米团簇其熔点随尺寸单调增加,而较小原子数目的团簇熔点和尺寸呈现无规则变化;大多数团簇在熔点附近都出现了负热容现象,说明负热容是纳米团簇在熔化过程中的一个普遍现象.     

Clustering and Dissolution of Small Helium Clusters in Bulk Tungsten

Density functional theory calculations are conducted to investigate the stability and interactions among small helium(He) clusters in bulk tungsten(W).The lowest energy structure of each cluster for sizes 9) = 1 to 6 is determined.With the formation of He clusters,He defects form in bulk W.The thermodynamics of the clusters are investigated in the temperature range of 1000–2300 K using molecular dynamics.This study provides the information essential to understand small He cluster behavior in bulk W.     

系列含钨原子簇化合物的红外光谱研究

本文报道了系列两核或四核的含钨原子簇化合物的红外光谱的研究结果。通过对这些化合物的光谱数据分析并结合它们的结构特征,归属了这些含有「Ｗ２Ｓ４」＾２＋和「Ｗ２ＭＭ’Ｓ４」＾４＋（Ｍ,Ｍ’＝Ｃｕ,Ａｇ）簇芯的原子簇化合物的主要振动谱峰,并讨论了结构的变化对光谱的影响。     

小尺寸金属钨团簇的密度泛函研究

在相对论原子实势(RECP)近似下,采用密度泛函理论B3LYP方法对Wn(n=2~7)团簇进行优化,得出稳定的平衡几何结构。并计算了垂直电离能,最高占据轨道(HOMO)与最低非占据轨道(LOMO)之间的能隙。得出小尺寸金属钨团簇失去电子的能力随原子个数的增加而增大,W3的稳定性最好的结论。     

Blistering and Helium Retention of Tungsten and 5% Chromium Doped Tungsten Exposed to 60 keV Helium Ions Irradiation

Pure tungsten(W) and chromium doped W(W-5%Cr) are prepared by powder metallurgy. The microstructure,blistering and helium retention are investigated by x-ray diffraction,scanning electron microscopy,transmission electron microscopy and thermal desorption spectroscopy(TDS). These results show that the average size and density of helium blisters on the surface of pure W are much larger than those on the W-5%Cr alloy. Vacancyimpurity pairs can reduce the migration coefficients of vacancy and vacancy-helium complexes, and Cr may play a role of such an impurity. Moreover, the TDS result shows that the highest desorption peak moves to higher temperature, which is attributed to the He_mCr_kV_n complexes in the W-Cr alloy. In addition,the helium retention is found to be higher in W than in W-5%Cr.     

He 离子注入引起的高纯钨硬化

完成了不同注量或温度下100 keV 的He 离子注入高纯钨的实验,并利用纳米压痕技术测量了材料的微观力学性能。所有注入样品的纳米硬度值都高于未注入样品的纳米硬度值。对于室温注入样品,随着注量的增加,样品抗弹性变形能力下降;当注量不高于5x1017 ions/cm2 时,钨的纳米硬度峰值随着注量的增加而增加;注量为1x1018 ions/cm2 的钨样品的纳米硬度峰值反而降低。高温注入样品的抗弹性变形能力优于室温注入样品的抗弹性变形能力;随着注入温度的增加,样品的平均纳米硬度值和弹性模量略有下降。分析讨论了He 注入钨硬化和抗弹性形变能力降低的可能原因。Tungsten has been selected as divertor materials in fusion reactors because of its high thermal conductivity,high melting point, low expansion coefficient and high threshold energy for sputtering etc. The paper presents the hardening behaviour of high pure tungsten by 100 keV He+ with different fluences from 5x1016 ions/cm2 to 1x1018ions/cm2 at room temperature, and with fluence of 1x1018 ions/cm2 at higher temperatures (400, 600 and 800 °C). The microscopic mechanical properties of these samples were investigated by nano-indentation technology. The results show that all of the implanted samples harden obviously. The reason for hardening may be that defects of interstitial dislocation loops or dense helium bubbles etc induced by helium implantation obstacle the movement of dislocation. The peak nanohardness of the samples increased with the fluences increasing when the fluence is not more than 5x1017 ions/cm2, while the nano-hardness value of the implanted sample with the fluence of 1x1018 ions/cm2 decreases and the nano-hardness changes little in the region of 50 nm to 200 nm from surface. For all the implanted samples with 1x1018 ions/cm2 at higher temperatures, their nano-hardness values are similar, but show a trend of decrease with increasing temperature.The reason may be the decrease of the defects’ density during implantation at higher temperatures. In addition, the capability of resisting deformation for the implanted tungsten reduces with increasing fluence and increases a little at higher temperatures.     

Generation of Lithium Clusters in Helium Plasma Flow

Technical Physics - The formation of lithium clusters in a helium flow is considered within the method considering the widths of energy levels. It is shown that lithium atoms in a plasma flow of...     

单轴应力场下钨中氦扩散行为的分子动力学模拟研究

本文采用分子动力学方法研究了沿<100>及<111>晶向的单轴应变对钨中单个氦原子扩散的影响。结果表明,应变会使得金属钨材料发生相变,且引起相变的临界应变随温度升高而减小。相变起始的应变在达到抗拉强度的应变附近。计算结果表明,拉应变使得单个氦原子在钨中的扩散系数发生骤降,在不同应变下扩散系数变化平缓。沿<100>晶向氦扩散系数随应变的增大而线性减小,而<111>晶向则出现了震荡变化趋势。研究结果表明,沿<100>晶向应变达到+0.15%时阿纽列斯方程不再适用,而沿<111>晶向应变大+5%阿纽列斯方程仍然适用;沿<111>晶向随应变增加氦扩散激活能减小,说明应变使得单个氦原子在钨中迁移性增强。     

过渡金属锆铁对钨中氢氦行为的影响

钨被广泛地认为是最具潜力的面向等离子体材料。钨在聚变堆中的服役过程中,会受到强束低能的氢氦粒子流的影响,其结果是钨的性能下降。本工作通过第一性原理计算的方法研究了过渡金属锆铁对钨中氢氦行为的影响。研究结果表明,锆或铁的掺入会使钨的机械强度降低,延展性增加;锆铁的掺入不会改变氢氦在钨中的最佳占位,但是它们对氢氦在钨中的稳定性有一定影响;锆和铁对钨中氢氦的捕获作用存在一个最佳作用半径;铁原子在短距离（< 3.626 Å）时对氦有捕获作用,在长距离（> 3.626 Å）时存在排斥作用,而锆对钨中氢氦均具有捕获作用;钨中氢表现为亲电子的性质,而氦表现出疏电子的特性。总体上讲,锆对钨中氢氦的捕获作用要强于铁对钨中氢氦的捕获作用。本研究工作能够为钨基面向等离子体材料制备提供理论指导。Tungsten was widely considered as a highly promising candidate of plasma facing material, while the presence of hydrogen and helium has an adverse effect on the performance of the tungsten. The effects of transition metals (zirconium, iron) on the behavior of hydrogen and helium in tungsten were investigated by using the first-principles calculation method. The results show that doping of zirconium and iron decreases the mechanical strength of tungsten a little, but they increase the ductility of tungsten; zirconium and iron can't change the best occupied site of hydrogen and helium in tungsten, but they have some effect on the stability of the point defects formed by hydrogen and helium in tungsten; there is the best attraction radius between the transition metals (zirconium, iron) and hydrogen or helium in tungsten; there is an attractive interaction between iron and helium in a short distance (<3.626 Å), but a repulsion interaction in a long distance (>3.626 Å). An attractive interaction exists between zirconium and helium or hydrogen in tungsten whatever the distance is; the hydrogen that in tungsten has an electrophilic nature, while the helium has opposite features. The attraction interaction between zirconium and hydrogen or helium in tungsten is stronger than that of iron. Our works in this paper might provide a theory guide for the selection and preparation of the tungsten based alloy that is used as the plasma facing materials.     

Erratum to: Generation of Lithium Clusters in Helium Plasma Flow

Technical Physics - erratum     

Ranges of Hydrogen,Deuterium, and Helium Atoms in Amorphous Silicon and Tungsten

Technical Physics - We have obtained the range distributions for H, D, and He atoms within an energy range of 0.1–100 keV in amorphous W and Si for the normal incidence of bombarding...