| 1. |
- Li, Wei, et al.
(författare)
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Generalized stacking fault energy of gamma-Fe
- 2016
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Ingår i: Philosophical Magazine. - : Taylor & Francis. - 1478-6435 .- 1478-6443. ; 96:6, s. 524-541
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the generalized stacking fault energy ( [GRAPHICS] -surface) of paramagnetic [GRAPHICS] -Fe as a function of temperature. At static condition, the face-centred cubic (fcc) lattice is thermodynamically unstable with respect to the hexagonal close-packed lattice, resulting in a negative intrinsic stacking fault energy (ISF). However, the unstable stacking fault energy (USF), representing the energy barrier along the [GRAPHICS] -surface connecting the ideal fcc and the intrinsic stacking fault positions, is large and positive. The ISF is calculated to have a strong positive temperature coefficient, while the USF decreases monotonously with temperature. According to the recent plasticity theory, the overall effect of temperature is to move paramagnetic fcc Fe from the stacking fault formation regime ( [GRAPHICS] K) towards maximum twinning ( [GRAPHICS] K) and finally to a dominating full-slip regime ( [GRAPHICS] K). Our predictions are discussed in connection with the available experimental observations.
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| 2. |
- Laukkanen, P., et al.
(författare)
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Core-level shifts of the c(8 x 2)-reconstructed InAs(100) and InSb(100) surfaces
- 2010
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 177:1, s. 52-57
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Tidskriftsartikel (refereegranskat)abstract
- We have studied In-stabilized c(8 2)-reconstructed InAs(1 0 0) and InSb(1 0 0) semiconductor surfaces, which play a key role in growing improved III-V interfaces for electronics devices, by core-level photoelectron spectroscopy and first-principles calculations. The calculated surface core-level shifts (SCLSs) for the zeta and zeta a models, which have been previously established to describe the atomic structures of the III-V(1 00)c(8 x 2) surfaces, yield hitherto not reported interpretation for the As 3d, In 4d, and Sb 4d core-level spectra of the III-V(1 00)c(8 x 2) surfaces, concerning the number and origins of SCLSs. The fitting analysis of the measured spectra with the calculated zeta and zeta a SCLS values shows that the InSb spectra are reproduced by the zeta SCLSs better than by the zeta a SCLSs. Interestingly, the zeta a fits agree better with the InAs spectra than the zeta fits do, indicating that the zeta a model describes the InAs surface better than the InSb surface. These results are in agreement with previous X-ray diffraction data. Furthermore, an introduction of the complete-screening model, which includes both the initial and final state effects, does not improve the fitting of the InSb spectra, proposing the suitability of the initial-state model for the SCLSs of the III-V(1 0 0)c(8 x 2) surfaces. The found SCLSs are discussed with the ab initio on-site charges.
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| 3. |
- Huang, L., et al.
(författare)
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Anomalous temperature dependence of elastic constant c(44) in V, Nb, Ta, Pd, and Pt
- 2010
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Ingår i: Journal of Physics and Chemistry of Solids. - : Elsevier BV. - 0022-3697 .- 1879-2553. ; 71:8, s. 1065-1068
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Tidskriftsartikel (refereegranskat)abstract
- The anomalous temperature dependence of elastic constant c(44) for elements V. Nb, Ta, Pd, and Pt, has been calculated using first-principles theory. It is shown that the variation of elastic constant for simple elements can be approximated as the sum of thermal expansion and electronic components. The thermal expansion contributes the normal linearly decreasing effect to the elastic constant with temperature, while electronic contribution is determined by the unique character of electronic structure of elements and leads to the anomalous effect to the elastic constant with temperature.
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| 4. |
- Belonoshko, Anatoly, et al.
(författare)
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Properties of the fcc Lennard-Jones crystal model at the limit of superheating
- 2007
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 76:6, s. 064121-
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Tidskriftsartikel (refereegranskat)abstract
- The face-centered-cubic (fcc) Lennard-Jones (LJ) model can be considered as a representative model of a simple solid. We investigate the mechanism of melting at the limit of superheating in the fcc LJ solid by means of the procedure recently developed by us [Phys. Rev. B 73, 012201 (2006)]. Insight into the mechanism of melting was gained by studying diffusion and defects in the fcc LJ solid by means of molecular dynamics simulations. We found that the limit of superheating achieved by us is likely to be the highest so far. We also found that the size of the cluster which ignites the melting is very small (down to five to six atoms, depending on the size of the supercell) and closely correlates with the linear size of a supercell when the number of atoms varies between 500 and 13 500.
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| 5. |
- Belonoshko, Anatoly, et al.
(författare)
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Xenon melting: Density functional theory versus diamond anvil cell experiments
- 2006
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Ingår i: Physical Review B Condensed Matter. - : American Physical Society. - 0163-1829 .- 1095-3795. ; 74:5, s. 054114-
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Tidskriftsartikel (refereegranskat)abstract
- We performed two-phase ab initio density functional theory based molecular dynamics simulations of Xe melting and demonstrated that, contrary to claims in the recent literature, the pressure dependence of the Xe melting curve is consistent with the corresponding-states theory as well as with the melting curve obtained earlier from classical molecular dynamics with a Xe pair potential. While at low pressure the calculated melting curve is in perfect agreement with reliable experiments, our calculated melting temperatures at higher pressures are inconsistent with those from the most recent diamond anvil cell experiment. We discuss a possible explanation for this inconsistency.
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| 6. |
- Loa, I, et al.
(författare)
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Lattice Dynamics and Superconductivity in Cerium at High Pressure
- 2012
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 108:4, s. 045502-
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Tidskriftsartikel (refereegranskat)abstract
- We have measured phonon dispersion relations of the high-pressure phase cerium-oC(4) (alpha phase with the alpha-uranium crystal structure) at 6.5 GPa by using inelastic x-ray scattering. Pronounced phonon anomalies are observed, which are remarkably similar to those of alpha-U. First-principles electronic structure calculations reproduce the anomalies and allow us to identify strong electron-phonon coupling as their origin. At the low-pressure end of its stability range, Ce-oC4 is on the verge of a lattice-dynamical instability and possibly a charge density wave. The superconducting transition temperatures of the fcc, oC4, and mC4 phases of Ce have been calculated, and the superconductivity observed experimentally by Wittig and Probst is attributed to the oC4 phase.
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| 7. |
- Vitos, Levente, et al.
(författare)
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Alloying effects on the stacking fault energy in austenitic stainless steels from first-principles theory
- 2006
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 54:14, s. 3821-3826
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Tidskriftsartikel (refereegranskat)abstract
- The stacking fault energy (SFE) of austenitic stainless steels has been determined using a quantum mechanical first-principles approach. We identify the electronic, magnetic and volume effects responsible for the compositional dependence of the SFE. We find that both the alloying element and the composition of the host material are important for understanding the alloying effects. Our results show that no simple and universally valid composition equations exist for the SEE.
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| 8. |
- Andersson, David A., et al.
(författare)
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Modeling of Ce2, Ce2O3 ,and CeO2-x in the LDA+U formalism
- 2007
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 75, s. 035109-1-035109-6
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure and thermodynamic properties of CeO2 and Ce2O3 have been studied from first principles by the all-electron projector-augmented-wave (PAW) method, as implemented in the ab initio total-energy and molecular-dynamics program VASP (Vienna ab initio simulation package). The local density approximation (LDA)+U formalism has been used to account for the strong on-site Coulomb repulsion among the localized Ce 4f electrons. We discuss how the properties of CeO2 and Ce2O3 are affected by the choice of U as well as the choice of exchange-correlation potential, i.e., the local density approximation or the generalized gradient approximation. Further, reduction of CeO2, leading to formation of Ce2O3 and CeO2-x, and its dependence on U and exchange-correlation potential have been studied in detail. Our results show that by choosing an appropriate U it is possible to consistently describe structural, thermodynamic, and electronic properties of CeO2, Ce2O3, and CeO2-x, which enables modeling of redox processes involving ceria-based materials.
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| 9. |
- Andersson, David A., et al.
(författare)
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Redox properties of CeO2-MO2 MO2 (M=Ti, Zr, Hf or Th) solid solutions from first principles calculations
- 2007
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 90:3, s. 031909-
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Tidskriftsartikel (refereegranskat)abstract
- The authors have used density functional theory calculations to investigate how the redox thermodynamics and kinetics of CeO2 are influenced by forming solid solutions with TiO2, ZrO2, HfO2, and ThO2. Reduction is facilitated by dissolving TiO2 (largest improvement), HfO2, or ZrO2 (least improvement), while ThO2 makes reduction slightly more difficult. The migration barrier is much lower in the neighborhood of a Ti (largest decrease), Hf, or Zr (least decrease), while the binding energy of solute ions and vacancies increases in the same sequence. They rationalize the properties of ceria solid solutions in terms of defect cluster relaxations.
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| 10. |
- Andersson, David A., et al.
(författare)
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Theoretical study of CeO(2) doped with tetravalent ions
- 2007
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 76, s. 1741191-17411910
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Tidskriftsartikel (refereegranskat)abstract
- We have used density functional theory calculations within the LDA+U formulation to investigate how small amounts of dissolved SiO2, GeO2, SnO2, or PbO2 affect the redox thermodynamics of ceria (CeO2). Compared to pure ceria, reduction is facilitated and the reducibility increases in the sequence of CeO2-SnO2, CeO2-GeO2, and CeO2-SiO2, which correlates with the decrease of the ionic radii of the solutes. For low solute concentrations, there is an inverse relation between high reducibility and the solution energy of tetravalent solutes. CeO2-PbO2 is unique in the sense that the initial reduction occurs by Pb(IV)double right arrow Pb(II) instead of the usual Ce(IV)double right arrow Ce(III) reaction. Among the investigated ceria compounds, CeO2-PbO2 has the lowest reduction energy and rather low solution energy. We have studied how the solution and reduction energies depend on the concentration of Si, Ge, Sn, Pb, Ti, Zr, Hf, and Th solute ions. While the solution energy increases monotonously with concentration, the reduction energy first decreases, as compared to pure ceria (except for Th, which exhibits a small increase), and with further increase of solute concentration, it either remains almost constant (Zr, Hf, and Th) or slightly increases (Ti, Si, Ge, and Sn).
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