| 1. |
- Li, Ruihuan, et al.
(författare)
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Effects of Cr and W additions on the stability and migration of He in bcc Fe : A first-principles study
- 2016
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Ingår i: Computational materials science. - : Elsevier. - 0927-0256 .- 1879-0801. ; 123, s. 85-92
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Tidskriftsartikel (refereegranskat)abstract
- Density functional theory calculations have been performed to study the effects of alloying Cr and W on the stability and diffusivity of interstitial He impurity in body-centered cubic (bcc) Fe host lattice. The interaction between two close Cr/W atoms is repulsive. The relative stable position for an interstitial He remains the tetrahedral interstitial site in the presence Cr. Energetically, He prefers to locate far away from W inside Fe host lattice due to the strong repulsive interaction between He and W. On the other hand, the He migration barrier becomes lower in the presence of Cr (0.026 eV) and W(0.049 eV), as compared to 0.059 eV for pure Fe. Addition of Cr is benefit for He self-trapping, while W is against. The effective diffusivity of He decreases with increasing Cr and W concentrations. Moreover, the additions of Cr and W slightly hinder He being trapped by monovacancy.
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| 2. |
- Li, Ruihuan, et al.
(författare)
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Stacking fault energy of face-centered cubic metals : thermodynamic and ab initio approaches
- 2016
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Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 28:39
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Tidskriftsartikel (refereegranskat)abstract
- The formation energy of the interface between face-centered cubic (fcc) and hexagonal close packed (hcp) structures is a key parameter in determining the stacking fault energy (SFE) of fcc metals and alloys using thermodynamic calculations. It is often assumed that the contribution of the planar fault energy to the SFE has the same order of magnitude as the bulk part, and thus the lack of precise information about it can become the limiting factor in thermodynamic predictions. Here, we differentiate between the interfacial energy for the coherent fcc(1 1 1)/hcp(0 0 0 1) interface and the 'pseudo-interfacial energy' that enters the thermodynamic expression for the SFE. Using first-principles calculations, we determine the coherent and pseudo-interfacial energies for six elemental metals (A1, Ni, Cu, Ag, Pt, and Au) and three paramagnetic Fe-Cr-Ni alloys. Our results show that the two interfacial energies significantly differ from each other. We observe a strong chemistry dependence for both interfacial energies. The calculated pseudo-interfacial energies for the Fe-Cr-Ni steels agree well with the available literature data. We discuss the effects of strain on the description of planar faults via thermodynamic and ab initio approaches.
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| 3. |
- Li, Xiaojie, et al.
(författare)
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Ab initio calculations of mechanical properties of bcc W-Re-Os random alloys : effects of transmutation of W
- 2016
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Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 28:29
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Tidskriftsartikel (refereegranskat)abstract
- To examine the effect of neutron transmutation on tungsten as the first wall material of fusion reactors, the elastic properties of W1-x-yRexOsy (0 <= x, y <= 6%) random alloys in body centered cubic (bcc) structure are investigated systematically using the all-electron exact muffin-tin orbitals (EMTO) method in combination with the coherent-potential approximation (CPA). The calculated lattice constant and elastic properties of pure W are consistent with available experiments. Both Os and Re additions reduce the lattice constant and increase the bulk modulus of W, with Os having the stronger effect. The polycrystalline shear modulus, Young's modulus and the Debye temperature increase (decrease) with the addition of Re (Os). Except for C-11, the other elastic parameters including C-12, C-44, Cauchy pressure, Poisson ratio, B/G, increase as a function of Re and Os concentration. The variations of the latter three parameters and the trend in the ratio of cleavage energy to shear modulus for the most dominant slip system indicate that the ductility of the alloy enhances with increasing Re and Os content. The calculated elastic anisotropy of bcc W slightly increases with the concentration of both alloying elements. The estimated melting temperatures of the W-Re-Os alloy suggest that Re or Os addition will reduce the melting temperature of pure W solid. The classical Labusch-Nabarro model for solid-solution hardening predicts larger strengthening effects in W1-yOsy than in W1-xRex. A strong correlation between C' and the fcc-bcc structural energy difference for W1-x-yRexOsy is revealed demonstrating that canonical band structure dictates the alloying effect on C'. The structural energy difference is exploited to estimate the alloying effect on the ideal tensile strength in the [0 0 1] direction.
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| 4. |
- Liu, Jinxuan, et al.
(författare)
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A new class of epitaxial porphyrin metal-organic framework thin films with extremely high photocarrier generation efficiency : promising materials for all-solid-state solar cells
- 2016
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 4:33, s. 12739-12747
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the fabrication of a new class of epitaxial porphyrin metal-organic framework thin films whose photophysical properties can be tuned by the introduction of electron-donating diphenylamine (DPA) groups into the porphyrin skeleton. The attachment of DPA groups results in strongly improved absorption characteristics, yielding the highest photocarrier generation efficiency reported so far. DFT calculations identify a shift of the charge localization pattern in the VBM (lowest unoccupied molecular orbital), confirming that the introduction of the DPA groups is the main reason for the shift of the optical absorption spectrum and the improved photocurrent generation.
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