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Sergei L. Dudarev - One of the best experts on this subject based on the ideXlab platform.
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multiscale modeling of crowdion and vacancy defects in body centered cubic transition metals
Physical Review B, 2007Co-Authors: P M Derlet, D Nguyenmanh, Sergei L. DudarevAbstract:We investigate the structure and mobility of single self-Interstitial Atom and vacancy defects in body-centered-cubic transition metals forming groups 5B (vanadium, niobium, and tantalum) and 6B (chromium, molybdenum, and tungsten) of the Periodic Table. Density-functional calculations show that in all these metals the axially symmetric self-Interstitial Atom configuration has the lowest formation energy. In chromium, the difference between the energies of the and the self-Interstitial configurations is very small, making the two structures almost degenerate. Local densities of states for the Atoms forming the core of crowdion configurations exhibit systematic widening of the "local" d band and an upward shift of the antibonding peak. Using the information provided by electronic structure calculations, we derive a family of Finnis-Sinclair-type interAtomic potentials for vanadium, niobium, tantalum, molybdenum, and tungsten. Using these potentials, we investigate the thermally activated migration of self-Interstitial Atom defects in tungsten. We rationalize the results of simulations using analytical solutions of the multistring Frenkel-Kontorova model describing nonlinear elastic interactions between a defect and phonon excitations. We find that the discreteness of the crystal lattice plays a dominant part in the picture of mobility of defects. We are also able to explain the origin of the non-Arrhenius diffusion of crowdions and to show that at elevated temperatures the diffusion coefficient varies linearly as a function of absolute temperature.
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self Interstitial Atom defects in bcc transition metals group specific trends
Physical Review B, 2006Co-Authors: D Nguyenmanh, Andrew P. Horsfield, Sergei L. DudarevAbstract:We present an investigation of systematic trends for the self-Interstitial Atom (SIA) defect behavior in body-centered cubic (bcc) transition metals using density-functional calculations. In all the nonmagnetic bcc metals the most stable SIA defect configuration has the symmetry. Metals in group 5B of the periodic table (V, Nb, Ta) have significantly different energies of formation of the and SIA configurations, while for the group 6B metals (Cr, Mo, W) the two configurations are linked by a soft bending mode. The relative energies of SIA defects in the nonmagnetic bcc metals are fundamentally different from those in ferromagnetic bcc {alpha}-Fe. The systematic trend exhibited by the SIA defect structures in groups 5B and 6B transition metals correlates with the observed thermally activated mobility of SIA defects.
Sa Ringel - One of the best experts on this subject based on the ideXlab platform.
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unusual formation of point defect complexes in the ultrawide band gap semiconductor β ga 2 o 3
Physical Review X, 2019Co-Authors: Jared M Johnson, Ar Arehart, Zhen Chen, Joel B Varley, Christine Jackson, Esmat Farzana, Z Zhang, Hsienlien Huang, Arda Genc, Sa RingelAbstract:Author(s): Johnson, JM; Chen, Z; Varley, JB; Jackson, CM; Farzana, E; Zhang, Z; Arehart, AR; Huang, HL; Genc, A; Ringel, SA; Van De Walle, CG; Muller, DA; Hwang, J | Abstract: Understanding the unique properties of ultra-wide band gap semiconductors requires detailed information about the exact nature of point defects and their role in determining the properties. Here, we report the first direct microscopic observation of an unusual formation of point defect complexes within the Atomic-scale structure of β-Ga2O3 using high resolution scanning transmission electron microscopy (STEM). Each complex involves one cation Interstitial Atom paired with two cation vacancies. These divacancy-Interstitial complexes correlate directly with structures obtained by density functional theory, which predicts them to be compensating acceptors in β-Ga2O3. This prediction is confirmed by a comparison between STEM data and deep level optical spectroscopy results, which reveals that these complexes correspond to a deep trap within the band gap, and that the development of the complexes is facilitated by Sn doping through increased vacancy concentration. These findings provide new insight on this emerging material's unique response to the incorporation of impurities that can critically influence their properties.
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Unusual Formation of Point-Defect Complexes in the Ultrawide-Band-Gap Semiconductor β-Ga2 O3
eScholarship University of California, 2019Co-Authors: Jm Johnson, Chen Z, Jb Varley, Cm Jackson, Farzana E, Zhang Z, Ar Arehart, Hl Huang, Genc A, Sa RingelAbstract:Understanding the unique properties of ultra-wide band gap semiconductors requires detailed information about the exact nature of point defects and their role in determining the properties. Here, we report the first direct microscopic observation of an unusual formation of point defect complexes within the Atomic-scale structure of β-Ga2O3 using high resolution scanning transmission electron microscopy (STEM). Each complex involves one cation Interstitial Atom paired with two cation vacancies. These divacancy-Interstitial complexes correlate directly with structures obtained by density functional theory, which predicts them to be compensating acceptors in β-Ga2O3. This prediction is confirmed by a comparison between STEM data and deep level optical spectroscopy results, which reveals that these complexes correspond to a deep trap within the band gap, and that the development of the complexes is facilitated by Sn doping through increased vacancy concentration. These findings provide new insight on this emerging material's unique response to the incorporation of impurities that can critically influence their properties
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Unusual Formation of Point-Defect Complexes in the Ultrawide-Band-Gap Semiconductor β-Ga2 O3
eScholarship University of California, 2019Co-Authors: Jm Johnson, Chen Z, Jb Varley, Cm Jackson, Farzana E, Zhang Z, Ar Arehart, Hl Huang, Genc A, Sa RingelAbstract:© 2019 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "https://creativecommons.org/licenses/by/4.0/" Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Understanding the unique properties of ultra-wide band gap semiconductors requires detailed information about the exact nature of point defects and their role in determining the properties. Here, we report the first direct microscopic observation of an unusual formation of point defect complexes within the Atomic-scale structure of β-Ga2O3 using high resolution scanning transmission electron microscopy (STEM). Each complex involves one cation Interstitial Atom paired with two cation vacancies. These divacancy-Interstitial complexes correlate directly with structures obtained by density functional theory, which predicts them to be compensating acceptors in β-Ga2O3. This prediction is confirmed by a comparison between STEM data and deep level optical spectroscopy results, which reveals that these complexes correspond to a deep trap within the band gap, and that the development of the complexes is facilitated by Sn doping through increased vacancy concentration. These findings provide new insight on this emerging material's unique response to the incorporation of impurities that can critically influence their properties
Katsuyuki Suzuki - One of the best experts on this subject based on the ideXlab platform.
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behavior of a self Interstitial Atom type dislocation loop in the periphery of an edge dislocation in bcc fe
Nuclear materials and energy, 2016Co-Authors: Sho Hayakawa, Taira Okita, Mitsuhiro Itakura, Masaatsu Aichi, S Fujita, Katsuyuki SuzukiAbstract:Abstract The behavior of the dislocation loop of a self-Interstitial Atom (SIA) near an edge dislocation and its conservative climb process were modeled in body-centered cubic Fe by incorporating loop rotation. The stable position of the loop and its rotational angle due to the interaction with an edge dislocation were evaluated through molecular dynamics simulations and calculations of the isotropic elasticity. The results were used as input variables in kinetic Monte Carlo simulations to model the absorption of the loop by the dislocation via a conservative climb. Loop rotation was found to affect the velocity of the conservative climb only at short-distances because the gradient in the interaction energy between the dislocation and an Atom at the edge of the loop, which is a driving force of the conservative climb, could not be precisely evaluated without loop rotation. Depending on the distance between the dislocation and the loop, allowing the loop rotation resulted in either an increase or decrease in the velocity of the conservative climb.
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Effects of stacking fault energy on defect formation process in face-centered cubic metals
Philosophical Magazine, 2016Co-Authors: Taira Okita, Mitsuhiro Itakura, Yingjuan Yang, Junichi Hirabayashi, Katsuyuki SuzukiAbstract:AbstractTo elucidate the effect of stacking fault energies (SFEs) on defect formation by the collision cascade process for face-centred cubic metals, we used six sets of interAtomic potentials with different SFEs while keeping the other properties almost identical. Molecular dynamic simulations of the collision cascade were carried out using these potentials with primary knock-on Atom energies (EPKA) of 10 and 20 keV at 100 K. Neither the number of residual defects nor the size distributions for both self-Interstitial Atom (SIA) type and vacancy type clusters were affected by the difference in the SFE. In the case of EPKA = 20 keV, the ratio of glissile SIA clusters increased as the SFE decreased, which was not expected by a prediction based on the classical dislocation theory. The trend did not change after annealing at 1100 K for 100 ps. For vacancy clusters, few stacking fault tetrahedrons (SFTs) formed before the annealing. However, lower SFEs tended to increase the SFT fraction after the annealing, w...
S L Dudarev - One of the best experts on this subject based on the ideXlab platform.
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Quantum de-trapping and transport of heavy defects in tungsten
'Springer Science and Business Media LLC', 2020Co-Authors: Arakawa K, S L Dudarev, Marinica M-c, Fitzgerald S, Proville L, Nguyen-manh D, Ma P-w, Td Swinburne, Am Goryaeva, Yamada TAbstract:The diffusion of defects in crystalline materials1 controls macroscopic behaviour of a wide range of processes, including alloying, precipitation, phase transformation and creep2. In real materials, intrinsic defects are unavoidably bound to static trapping centres such as impurity Atoms, meaning that their diffusion is dominated by de-trapping processes. It is generally believed that de-trapping occurs only by thermal activation. Here, we report the direct observation of the quantum de-trapping of defects below around one-third of the Debye temperature. We successfully monitored the de-trapping and migration of self-Interstitial Atom clusters, strongly trapped by impurity Atoms in tungsten, by triggering de-trapping out of equilibrium at cryogenic temperatures, using high-energy electron irradiation and in situ transmission electron microscopy. The quantum-assisted de-trapping leads to low-temperature diffusion rates orders of magnitude higher than a naive classical estimate suggests. Our analysis shows that this phenomenon is generic to any crystalline material
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universality of point defect structure in body centered cubic metals
Physical Review Materials, 2019Co-Authors: S L DudarevAbstract:Density functional theory calculations show that the lowest energy structure of a self-Interstitial Atom defect is universal to all the nonmagnetic bcc metals. The defects adopt linear configurations with the orientation of their axes. The formation and migration energies, elastic dipole tensors, and relaxation volumes of all the point defects in all the bcc metals are tabulated in a form suitable for macroscopic simulations, for example, for predicting radiation-induced swelling. The authors also show how elastic relaxation parameters vary along the defect migration pathways.
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elastic fields dipole tensors and interaction between self Interstitial Atom defects in bcc transition metals
Physical Review Materials, 2018Co-Authors: S L DudarevAbstract:Density functional theory (DFT) calculations show that self-Interstitial Atom (SIA) defects in nonmagnetic body-centered-cubic (bcc) metals adopt strongly anisotropic configurations, elongated in the $\ensuremath{\langle}111\ensuremath{\rangle}$ direction [S. Han et al., Phys. Rev. B 66, 220101 (2002); D. Nguyen-Manh et al., Phys. Rev. B 73, 020101 (2006); P. M. Derlet et al., Phys. Rev. B 76, 054107 (2007); S. L. Dudarev, Annu. Rev. Mater. Res. 43, 35 (2013)]. Elastic distortions, associated with such anisotropic Atomic structures, appear similar to distortions around small prismatic dislocation loops, although the extent of this similarity has never been quantified. We derive analytical formulas for the dipole tensors of SIA defects, which show that, in addition to the prismatic dislocation looplike character, the elastic field of a SIA defect also has a significant isotropic dilatation component. Using empirical potentials and DFT calculations, we parametrize dipole tensors of $\ensuremath{\langle}111\ensuremath{\rangle}$ defects for all the nonmagnetic bcc transition metals. This enables a quantitative evaluation of the energy of elastic interaction between the defects, which also shows that in a periodic three-dimensional simple cubic arrangement of crowdions, long-range elastic interactions between a defect and all its images favor a $\ensuremath{\langle}111\ensuremath{\rangle}$ orientation of the defect.
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million Atom molecular dynamics simulations of magnetic iron
Progress in Materials Science, 2007Co-Authors: P M Derlet, S L DudarevAbstract:The problem of large-scale molecular dynamics simulations of iron has recently attracted attention in connection with the need to understand the microscopic picture of radiation damage in ferritic steels. In this paper we review the development of a new interAtomic potential for magnetic iron, and describe the first large-scale Atomistic simulations performed using the new method. We investigate the structure and thermally activated mobility of self-Interstitial Atom clusters and show that the spatial distribution of magnetic moments around a cluster is well correlated with the distribution of hydrostatic pressure, highlighting the significant part played by magneto-elasticity in the treatment of radiation damage. We show that self-Interstitial Atom clusters exhibit a transition from relatively immobile configurations containing (1 1 0)-like groups of Atoms to (1 1 1)-like configurations occurring at a critical cluster size N-c similar to 5 Atoms. We discuss implications of this finding for the treatment of cascade damage effects, and the possibility of observing new low-temperature resistivity recovery stages in neutron-irradiated alpha-iron. (C) 2006 Elsevier Ltd. All rights reserved.
D Nguyenmanh - One of the best experts on this subject based on the ideXlab platform.
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multiscale modeling of crowdion and vacancy defects in body centered cubic transition metals
Physical Review B, 2007Co-Authors: P M Derlet, D Nguyenmanh, Sergei L. DudarevAbstract:We investigate the structure and mobility of single self-Interstitial Atom and vacancy defects in body-centered-cubic transition metals forming groups 5B (vanadium, niobium, and tantalum) and 6B (chromium, molybdenum, and tungsten) of the Periodic Table. Density-functional calculations show that in all these metals the axially symmetric self-Interstitial Atom configuration has the lowest formation energy. In chromium, the difference between the energies of the and the self-Interstitial configurations is very small, making the two structures almost degenerate. Local densities of states for the Atoms forming the core of crowdion configurations exhibit systematic widening of the "local" d band and an upward shift of the antibonding peak. Using the information provided by electronic structure calculations, we derive a family of Finnis-Sinclair-type interAtomic potentials for vanadium, niobium, tantalum, molybdenum, and tungsten. Using these potentials, we investigate the thermally activated migration of self-Interstitial Atom defects in tungsten. We rationalize the results of simulations using analytical solutions of the multistring Frenkel-Kontorova model describing nonlinear elastic interactions between a defect and phonon excitations. We find that the discreteness of the crystal lattice plays a dominant part in the picture of mobility of defects. We are also able to explain the origin of the non-Arrhenius diffusion of crowdions and to show that at elevated temperatures the diffusion coefficient varies linearly as a function of absolute temperature.
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self Interstitial Atom defects in bcc transition metals group specific trends
Physical Review B, 2006Co-Authors: D Nguyenmanh, Andrew P. Horsfield, Sergei L. DudarevAbstract:We present an investigation of systematic trends for the self-Interstitial Atom (SIA) defect behavior in body-centered cubic (bcc) transition metals using density-functional calculations. In all the nonmagnetic bcc metals the most stable SIA defect configuration has the symmetry. Metals in group 5B of the periodic table (V, Nb, Ta) have significantly different energies of formation of the and SIA configurations, while for the group 6B metals (Cr, Mo, W) the two configurations are linked by a soft bending mode. The relative energies of SIA defects in the nonmagnetic bcc metals are fundamentally different from those in ferromagnetic bcc {alpha}-Fe. The systematic trend exhibited by the SIA defect structures in groups 5B and 6B transition metals correlates with the observed thermally activated mobility of SIA defects.
