The Experts below are selected from a list of 86844 Experts worldwide ranked by ideXlab platform
Hsinyi Lee - One of the best experts on this subject based on the ideXlab platform.
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calculation of point defects in rutile tio 2 by the screened exchange hybrid functional
Physical Review B, 2012Co-Authors: Hsinyi Lee, S J Clark, J RobertsoAbstract:The formation energies of the oxygen Vacancy and titanium interstitial in rutile TiO 2 were calculated by the screened-exchange (sX) hybrid density functional method, which gives a band gap of 3.1 eV, close to the experimental value. The oxygen Vacancy gives rise to a gap state lying 0.7 eV below the conduction band edge, whose charge density is localized around the two of three Ti atoms next to the Vacancy. The Ti interstitial (Ti int) generates four defect states in the gap, whose unpaired electrons lie on the interstitial and the adjacent Ti 3d orbitals. The formation energy for the neutral oxygen Vacancy is 1.9 eV for the O-poor chemical potential. The neutral Ti interstitial has a lower formation energy than the O Vacancy under O-poor conditions. This indicates that both the O Vacancy and Ti int are relevant for oxygen deficiency in rutile TiO 2 but the O Vacancy will dominate under O-rich conditions. This resolves questions about defect localization and defect predominance in the literature. © 2012 American Physical Society.
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calculation of point defects in rutile tio 2 by the screened exchange hybrid functional
Physical Review B, 2012Co-Authors: Hsinyi Lee, S J Clark, J RobertsonAbstract:The formation energies of the oxygen Vacancy and titanium interstitial in rutile TiO${}_{2}$ were calculated by the screened-exchange (sX) hybrid density functional method, which gives a band gap of 3.1 eV, close to the experimental value. The oxygen Vacancy gives rise to a gap state lying 0.7 eV below the conduction band edge, whose charge density is localized around the two of three Ti atoms next to the Vacancy. The Ti interstitial (Ti${}_{\mathrm{int}}$) generates four defect states in the gap, whose unpaired electrons lie on the interstitial and the adjacent Ti 3$d$ orbitals. The formation energy for the neutral oxygen Vacancy is 1.9 eV for the O-poor chemical potential. The neutral Ti interstitial has a lower formation energy than the O Vacancy under O-poor conditions. This indicates that both the O Vacancy and Ti${}_{\mathrm{int}}$ are relevant for oxygen deficiency in rutile TiO${}_{2}$ but the O Vacancy will dominate under O-rich conditions. This resolves questions about defect localization and defect predominance in the literature.
Ying Zhang - One of the best experts on this subject based on the ideXlab platform.
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hydrogen behaviors in molybdenum and tungsten and a generic Vacancy trapping mechanism for h bubble formation
Journal of Nuclear Materials, 2013Co-Authors: Lu Sun, Shuo Jin, Ying ZhangAbstract:Abstract We investigate the trapping behaviors of hydrogen (H) in molybdenum (Mo) and tungsten (W) using a first-principles method with a zero point energy correction as well as the molecular dynamics (MD) method. The H trapping is found to generally satisfy the “optimal charge density” rule at the Vacancy, and a monoVacancy is shown to simultaneously trap 14 H with a H 2 molecule formed at the Vacancy center in both Mo and W. On the other hand, the MD simulation shows the temperature decreases the number of trapped H at the Vacancy. We further propose a generic Vacancy trapping mechanism for H bubble formation in metals. The H atoms will first saturate the internal surface of the Vacancy (or other Vacancy-type defects) to form a “screening layer”, which can screen the interaction between the further trapped H and the surrounding metal atoms. This leads to the formation of H 2 molecule at the Vacancy center, which can be considered as the preliminary stage of H bubble nucleation.
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investigating behaviors of h in a w single crystal by first principles from solubility to interaction with Vacancy
Journal of Alloys and Compounds, 2011Co-Authors: Yue Lin Liu, Hong-bo Zhou, Ying ZhangAbstract:Abstract We have investigated structure and solubility of H, as well as H–Vacancy interaction in tungsten (W) single crystal employing a first-principles method. Single H atom is shown to be energetically favorable sitting at the tetrahedral interstitial site (TIS). The solubility of H is estimated in W according to the Sieverts’ law. We found that the solution concentrations are 2.3 × 10 −10 and 1.8 × 10 −7 at the typical temperatures of 600 K and 1000 K, respectively. The calculated results are basically consistent with the experiments. The Vacancy can be found to play a key role on the trapping of H in W. There exists a very strong binding between single H and Vacancy with the binding energy of 1.18 eV. With the H atoms added, the H n V complexes can be easily formed in the Vacancy. A monoVacancy is shown to be capable of trapping as many as 7 H atoms. Kinetically, we show that the H jumps into the Vacancy from the first nearest neighboring TIS into Vacancy with a much reduced barrier of 0.02 eV, which indicates a down-hill “drift” diffusion of H towards Vacancy. The physical mechanism underlying H assisted Vacancy formation is originated from that H atoms can stimulate the formation and growth of Vacancy or void by binding with Vacancy to decrease the effective formation energy of Vacancy in W.
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Vacancy trapping mechanism for hydrogen bubble formation in metal
Physical Review B, 2009Co-Authors: Yue Lin Liu, Hong-bo Zhou, Ying Zhang, Feng Liu, G N LuoAbstract:We reveal the microscopic Vacancy trapping mechanism for H bubble formation in W based on first-principles calculations of the energetics of H-Vacancy interaction and the kinetics of H segregation. Vacancy provides an isosurface of optimal charge density that induces collective H binding on its internal surface, a prerequisite for the formation of ${\text{H}}_{2}$ molecule and nucleation of H bubble inside the Vacancy. The critical H density on the Vacancy surface before the ${\text{H}}_{2}$ formation is found to be ${10}^{19}--{10}^{20}\text{ }\text{H}$ atoms per ${\text{m}}^{2}$. We believe that such mechanism is generally applicable for H bubble formation in metals and metal alloys.
G N Luo - One of the best experts on this subject based on the ideXlab platform.
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bubble growth from clustered hydrogen and helium atoms in tungsten under a fusion environment
Nuclear Fusion, 2017Co-Authors: Yuwei You, Xiangshan Kong, C S Liu, Jun Chen, G N LuoAbstract:Bubbles seriously degrade the mechanical properties of tungsten and thus threaten the safety of nuclear fusion devices, however, the underlying atomic mechanism of bubble growth from clustered hydrogen and helium atoms is still mysterious. In this work, first-principles calculations are therefore carried out to assess the stability of tungsten atoms around both hydrogen and helium clusters. We find that the closest Vacancy-formation energies of interstitial hydrogen and helium clusters are substantially decreased. The first-nearest and second-nearest Vacancy-formation energies close to Vacancy–hydrogen clusters decrease in a step-like way to ~0, while those close to Vacancy–helium clusters are reduced almost linearly to ~−5.46 eV when atom number reaches 10. The Vacancy-formation energies closest to helium clusters are more significantly reduced than those nearest to hydrogen clusters, whatever the clusters are embedded at interstitial sites or vacancies. The reduction of Vacancy-formation energies results in instability and thus emission of tungsten atoms close to interstitial helium and Vacancy–helium clusters, which illustrates the experimental results, that the tungsten atoms can be emitted from the vicinity of Vacancy–helium clusters. In addition, the emission of unstable tungsten atoms close to hydrogen clusters may become possible once they are disturbed by the environment. The emission of tungsten atoms facilitates the growth and evolution of hydrogen and helium clusters and ultimately the bubble formation. The results also explain the bubble formation even if no displacement damage is produced in tungsten exposed to low-energy hydrogen and helium plasma.
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energetic and kinetic dataset on interaction of the Vacancy and self interstitial atom with the grain boundary in α iron
Data in Brief, 2016Co-Authors: Wei Liu, B C Pan, C S Liu, Yunfeng Liang, G N LuoAbstract:We provide the dataset of the Vacancy (interstitial) formation energy, segregation energy, diffusion barrier, Vacancy-interstitial annihilation barrier near the grain boundary (GB) in bcc-iron and also the corresponding interactive range. The Vacancy-interstitial annihilation mechanisms in the bulk, near the GB and at the GB at across scales were given.
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Vacancy trapping mechanism for hydrogen bubble formation in metal
Physical Review B, 2009Co-Authors: Yue Lin Liu, Hong-bo Zhou, Ying Zhang, Feng Liu, G N LuoAbstract:We reveal the microscopic Vacancy trapping mechanism for H bubble formation in W based on first-principles calculations of the energetics of H-Vacancy interaction and the kinetics of H segregation. Vacancy provides an isosurface of optimal charge density that induces collective H binding on its internal surface, a prerequisite for the formation of ${\text{H}}_{2}$ molecule and nucleation of H bubble inside the Vacancy. The critical H density on the Vacancy surface before the ${\text{H}}_{2}$ formation is found to be ${10}^{19}--{10}^{20}\text{ }\text{H}$ atoms per ${\text{m}}^{2}$. We believe that such mechanism is generally applicable for H bubble formation in metals and metal alloys.
J Robertso - One of the best experts on this subject based on the ideXlab platform.
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calculation of point defects in rutile tio 2 by the screened exchange hybrid functional
Physical Review B, 2012Co-Authors: Hsinyi Lee, S J Clark, J RobertsoAbstract:The formation energies of the oxygen Vacancy and titanium interstitial in rutile TiO 2 were calculated by the screened-exchange (sX) hybrid density functional method, which gives a band gap of 3.1 eV, close to the experimental value. The oxygen Vacancy gives rise to a gap state lying 0.7 eV below the conduction band edge, whose charge density is localized around the two of three Ti atoms next to the Vacancy. The Ti interstitial (Ti int) generates four defect states in the gap, whose unpaired electrons lie on the interstitial and the adjacent Ti 3d orbitals. The formation energy for the neutral oxygen Vacancy is 1.9 eV for the O-poor chemical potential. The neutral Ti interstitial has a lower formation energy than the O Vacancy under O-poor conditions. This indicates that both the O Vacancy and Ti int are relevant for oxygen deficiency in rutile TiO 2 but the O Vacancy will dominate under O-rich conditions. This resolves questions about defect localization and defect predominance in the literature. © 2012 American Physical Society.
Robin Braun - One of the best experts on this subject based on the ideXlab platform.
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The equivalent Young's modulus prediction for Vacancy defected graphene under shear stress
Physica E-low-dimensional Systems & Nanostructures, 2019Co-Authors: Robin BraunAbstract:Abstract The uncertain and unavoidable Vacancy defects in graphene have the inevitable influence in the extraordinary intrinsic in-plane strength. In this paper, the equivalent Young's modulus is derived from the strain energy as an important factor to evaluate the stiffness of the entire graphene based on the mechanical molecular theory. The location of Vacancy defects in graphene is discussed in the regular deterministic and uncertain patterns. In terms of the boundary condition, shear stress is loaded in armchair and zigzag edges, respectively. The results show that the center concentrated Vacancy defects evidently deteriorate the elastic stiffness under shear stress. The influences of periodic and regular Vacancy defects are sensitive to the boundary condition. By the Monte Carlo based finite element method, Vacancy defects are dispersed randomly and propagated. The results of the equivalent Young's modulus are compared with the original values in pristine graphene. The interval and mean values of Young's modulus, total strain and energy density are also provided and discussed. Compared with the results of graphene with Vacancy defects under uniaxial tension, the enhancement effects of Vacancy defects are less evident in the graphene under shear stress.
