Molecular dynamics simulations are conducted to study self-interstitial migration in zirconium. By defining crystal lattice points where more than one atom is present in corresponding Wigner-Seitz cells, as the locati...Molecular dynamics simulations are conducted to study self-interstitial migration in zirconium. By defining crystal lattice points where more than one atom is present in corresponding Wigner-Seitz cells, as the locations of self-interstitial atoms （LSIAs）, three types of events are identified as LSIA migrations：the jump remaining in one 〈1120〉 direction （ILJ）, the jump from one 〈1120〉 to another 〈1120〉 direction in the same basal plane （OLJ）, and the jump from one basal plane to an adjacent basal plane （OPJ）. The occurrence frequencies of the three types are calculated. ILJ is found to be a dominant event in a temperature range from 300 K to 1200 K, but the occurrence frequencies of OLJ and OPJ increase with temperature increasing. The total occurrence frequency of all jump types has a good linear dependence on temperature. Moreover, the migration trajectories of LSIAs in the hcp basal-plane is not what is observed if only conventional one-or two-dimensional migrations exists; rather, they exhibit the feature that we call fraction-dimensional. Using Monte Carlo simulations, the potential kinetic effects of fraction-dimensional migration, which is measured by the average number of lattice sites visited per jump event （denoted by nSPE）, are analysed. The significant differences between the nSPE value of the fraction-dimensional migration and those of conventional one-and two-dimensional migrations suggest that the conventional diffusion coefficient cannot give an accurate description of the underlying kinetics of SIAs in Zr. This conclusion could be generally meaningful for the cases where the low-dimensional migration of defects are observed.展开更多
The behaviors of helium clusters and self-interstitial tungsten atoms at different temperatures are investigated with the molecular dynamics method. The self-interstitial tungsten atoms prefer to form crowdions which ...The behaviors of helium clusters and self-interstitial tungsten atoms at different temperatures are investigated with the molecular dynamics method. The self-interstitial tungsten atoms prefer to form crowdions which can tightly bind the helium cluster at low temperature. The crowdion can change its position around the helium cluster by rotating and slipping at medium temperatures, which leads to formation of combined crowdions or dislocation loop locating at one side of a helium cluster. The combined crowdions or dislocation loop even separates from the helium cluster at high temperature. It is found that a big helium cluster is more stable and its interaction with crowdions or dislocation loop is stronger.展开更多
Based on the density functional theory, we calculated the structures of the two main possible self-interstitial atoms（SIAs） as well as the migration energy of tungsten（W） atoms. It was found that the difference of...Based on the density functional theory, we calculated the structures of the two main possible self-interstitial atoms（SIAs） as well as the migration energy of tungsten（W） atoms. It was found that the difference of the 110 and 111 formation energies is 0.05–0.3 e V. Further analysis indicated that the stability of SIAs is closely related to the concentration of the defect. When the concentration of the point defect is high, 110 SIAs are more likely to exist, 111 SIAs are the opposite. In addition, the vacancy migration probability and self-recovery zones for these SIAs were researched by making a detailed comparison. The calculation provided a new viewpoint about the stability of point defects for selfinterstitial configurations and would benefit the understanding of the control mechanism of defect behavior for this novel fusion material.展开更多
Employing a first-principles method based on the density function theory, we systematically investigate the structures, stability and diffusion of self-interstitial atoms （SIAs） in tungsten （W）. The （111 〉 dumbb...Employing a first-principles method based on the density function theory, we systematically investigate the structures, stability and diffusion of self-interstitial atoms （SIAs） in tungsten （W）. The （111 〉 dumbbell is shown to be the most stable SIA defect configuration with the formation energy of -9.43 eV. The on-site rotation modes can be described by a quite soft floating mechanism and a down-hill ＂drift＂ diffusion process from （110） dumbbell to 〈111〉 dumbbell and from （001） dumbbell to 〈110〉 dumbbell, respectively. Among different SIA configurations jumping to near neighboring site, the 〈111 〉 dumbbell is more preferable to migrate directly to first-nearest-neighboring site with a much lower energy barrier of 0.004 eV. These resuits provide a useful reference for W as a candidate plasma facing material in fusion Tokamak.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.91126001)the National Magnetic Confinement Fusion Program of China(Grant No.2013GB109002)
文摘Molecular dynamics simulations are conducted to study self-interstitial migration in zirconium. By defining crystal lattice points where more than one atom is present in corresponding Wigner-Seitz cells, as the locations of self-interstitial atoms （LSIAs）, three types of events are identified as LSIA migrations：the jump remaining in one 〈1120〉 direction （ILJ）, the jump from one 〈1120〉 to another 〈1120〉 direction in the same basal plane （OLJ）, and the jump from one basal plane to an adjacent basal plane （OPJ）. The occurrence frequencies of the three types are calculated. ILJ is found to be a dominant event in a temperature range from 300 K to 1200 K, but the occurrence frequencies of OLJ and OPJ increase with temperature increasing. The total occurrence frequency of all jump types has a good linear dependence on temperature. Moreover, the migration trajectories of LSIAs in the hcp basal-plane is not what is observed if only conventional one-or two-dimensional migrations exists; rather, they exhibit the feature that we call fraction-dimensional. Using Monte Carlo simulations, the potential kinetic effects of fraction-dimensional migration, which is measured by the average number of lattice sites visited per jump event （denoted by nSPE）, are analysed. The significant differences between the nSPE value of the fraction-dimensional migration and those of conventional one-and two-dimensional migrations suggest that the conventional diffusion coefficient cannot give an accurate description of the underlying kinetics of SIAs in Zr. This conclusion could be generally meaningful for the cases where the low-dimensional migration of defects are observed.
基金Project supported by the Young Scientists Fund of the National Natural Science Foundation of China(Grant No.11705157)the Henan Provincial Key Research Projects,China(Grant No.17A140027)the Ninth Group of Key Disciplines in Henan Province of China(Grant No.2018119).
文摘The behaviors of helium clusters and self-interstitial tungsten atoms at different temperatures are investigated with the molecular dynamics method. The self-interstitial tungsten atoms prefer to form crowdions which can tightly bind the helium cluster at low temperature. The crowdion can change its position around the helium cluster by rotating and slipping at medium temperatures, which leads to formation of combined crowdions or dislocation loop locating at one side of a helium cluster. The combined crowdions or dislocation loop even separates from the helium cluster at high temperature. It is found that a big helium cluster is more stable and its interaction with crowdions or dislocation loop is stronger.
基金Project supported by the Fundamental Research Funds for the Central Universities of Ministry of Education of China(Grant Nos.A0920502051411-5 and2682014ZT30)the Program of International Science and Technology Cooperation,China(Grant No.2013DFA51050)+6 种基金the National Magnetic Confinement Fusion Science Program,China(Grant Nos.2011GB112001 and 2013GB110001)the National High Technology Research and Development Program of China(Grant No.2014AA032701)the National Natural Science Foundation of China(Grant No.11405138)the Southwestern Institute of Physics Funds,Chinathe Western Superconducting Technologies Company Limited,Chinathe Qingmiao Plan of Southwest Jiaotong University,China(Grant No.A0920502051517-6)the China Postdoctoral Science Foundation(Grant No.2014M560813)
文摘Based on the density functional theory, we calculated the structures of the two main possible self-interstitial atoms（SIAs） as well as the migration energy of tungsten（W） atoms. It was found that the difference of the 110 and 111 formation energies is 0.05–0.3 e V. Further analysis indicated that the stability of SIAs is closely related to the concentration of the defect. When the concentration of the point defect is high, 110 SIAs are more likely to exist, 111 SIAs are the opposite. In addition, the vacancy migration probability and self-recovery zones for these SIAs were researched by making a detailed comparison. The calculation provided a new viewpoint about the stability of point defects for selfinterstitial configurations and would benefit the understanding of the control mechanism of defect behavior for this novel fusion material.
基金supported by the National Natural Science Foundation of China (Grant No. 51061130558)the Fundamental Research Funds for the Central Universities
文摘Employing a first-principles method based on the density function theory, we systematically investigate the structures, stability and diffusion of self-interstitial atoms （SIAs） in tungsten （W）. The （111 〉 dumbbell is shown to be the most stable SIA defect configuration with the formation energy of -9.43 eV. The on-site rotation modes can be described by a quite soft floating mechanism and a down-hill ＂drift＂ diffusion process from （110） dumbbell to 〈111〉 dumbbell and from （001） dumbbell to 〈110〉 dumbbell, respectively. Among different SIA configurations jumping to near neighboring site, the 〈111 〉 dumbbell is more preferable to migrate directly to first-nearest-neighboring site with a much lower energy barrier of 0.004 eV. These resuits provide a useful reference for W as a candidate plasma facing material in fusion Tokamak.
