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  • 451.
    Zhang, Hualei
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Center of Microstructure Science, Frontier Institute of Science and Technology, State Key Laboratory for Mechanical Behavior of Materials, Xi'An Jiaotong University, Xi'an, China.
    Lu, Song
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Zhou, Minna
    Punkkinen, Marko P. J.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala Univ, Dept Phys & Mat Sci, Div Mat Theory, SE-75120 Uppsala, Sweden.
    Vitos, Levente
    Ab initio determination of the elastic properties of ferromagnetic body-centered cubic Fe-Mn-Al alloys2015Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 118, nr 10, artikel-id 103904Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The elastic properties of ferromagnetic Fe1-x-yMnyAlx (0 <= x <= 0.5, y = 0, 0.1, and 0.2) random solid solutions in the body-centered cubic (bcc) crystallographic phase have been investigated using the ab initio exact muffin-tin orbitals method in combination with the coherent-potential approximation. Comparison with the experimental data demonstrates that the employed theoretical approach accurately captures the observed composition dependence of the lattice parameter. The predicted elastic parameters follow complex composition dependence. The C-11, C-12, and C' = (C-11 - C-12)/2 single-crystal elastic constants, the bulk (B), shear (G), and Young's (E) moduli, and the Cauchy pressure (C-12 - C-44) mainly decrease with increasing Al content, whereas the Zener anisotropy ratio (C-44/C') strongly increases with x. C-44 exhibits a non-linear x dependence. The Poisson (v) and Pugh (B/G) ratios first decrease with x but show non-monotonous behavior in high-Al alloys. In terms of the Pugh criterion, these trends suggest an increased brittleness in Al-containing alloys. Manganese has a complex non-monotonous effect on B/G in low-Al alloys (below similar to 15 at. % Al) but enhances the brittleness of the bcc solid solution in large-Al regime. The peculiar Mn alloying effect is explained in terms of magneto-volume mechanisms.

  • 452.
    Zhang, Hualei
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Punkkinen, Marko P. J.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Theoretical elastic moduli of ferromagnetic bcc Fe alloys2010Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 22, nr 27, s. 275402-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The polycrystalline elastic parameters of ferromagnetic Fe1-xMx (M = Al, Si, V, Cr, Mn, Co, Ni, Rh; 0 <= x <= 0.1) random alloys in the body centered cubic (bcc) crystallographic phase have been calculated using first-principles alloy theory in combination with statistical averaging methods. With a few exceptions, the agreement between the calculated and the available experimental data for the polycrystalline aggregates is satisfactory. All additions considered here decrease the bulk modulus (B) and Poisson's ratio (nu) of bcc Fe. The complex composition dependence of the C-44 single-crystal elastic constant is reflected in the polycrystalline shear modulus (G), Young's modulus (E), and Debye temperature (Theta). The polycrystalline anisotropy of bcc Fe is increased by all additions, and Al, Si, Ni, and Rh yield the largest alloying effects.

  • 453.
    Zhang, Hualei
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Punkkinen, Marko Patrick John
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Hertzman, Staffan
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Single-crystal elastic constants of ferromagnetic bcc Fe-based random alloys from first-principles theory2010Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, nr 18, s. 184105-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The elastic properties of ferromagnetic Fe1-xMx (M=Al, Si, V, Cr, Mn, Co, Ni, and Rh; 0 <= x <= 0.1) random alloys in the body-centered-cubic (bcc) crystallographic phase have been studied using the all-electron exact muffin-tin orbitals method in combination with the coherent-potential approximation. The theoretical lattice parameters and the single-crystal elastic constants agree well with the available experimental data. The most significant alloying effects are found for Al, Si, and Ni additions. All elements enlarge the lattice parameter and decrease the C-11, C-12, and C' elastic constants and the bulk modulus of bcc Fe. At the same time, C-44 is found to increase with Al, Si, V, Cr, or Mn and remain nearly constant with Co, Ni, and Rh. Accordingly, the elastic anisotropy of bcc Fe increases with all alloying elements considered here. The calculated alloying effects on the single-crystal elastic constants are shown to originate from volume effects in combination with the peculiar electronic structure of bcc Fe.

  • 454.
    Zhang, Hualei
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Wang, Guisheng
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Punkkinen, Marko P. J.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Hertzman, Staffan
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Elastic anomalies in Fe-Cr alloys2013Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 25, nr 19, s. 195501-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using ab initio alloy theory, we determine the elastic parameters of ferromagnetic and paramagnetic Fe1-cCrc (0 <= c <= 1) alloys in the body centered cubic crystallographic phase. Comparison with the experimental data demonstrates that the employed theoretical approach accurately describes the observed composition dependence of the polycrystalline elastic moduli. The predicted single-crystal elastic constants follow complex anomalous trends, which are shown to originate from the interplay between magnetic and chemical effects. The nonmonotonic composition dependence of the elastic parameters has marked implications on the micro-mechanical properties of ferrite stainless steels.

  • 455. Zheng-Johansson, J. X.
    et al.
    Johansson, Börje
    The peaked structure of phonon density of states of a confined superfluid - a theoretical prediction, and discussions regarding its experimental probe2000Ingår i: Journal de Physique IV: Colloque, ISSN 1155-4339, E-ISSN 1764-7177, Vol. 10, nr P7, s. 181-184Artikel i tidskrift (Refereegranskat)
  • 456.
    Århammar, Cecilia
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Araujo, C. Moyses
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Rao, K. Venkat
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Norgren, S.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Energetics and magnetic properties of V-doped MgO bulk and (001) surface: A GGA, GGA+U, and hybrid density functional study2010Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, nr 13, s. 134406-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work, a first-principles study of the energetic and magnetic properties of V-doped MgO is presented, where both the bulk and (001) surface were investigated. It is found that V assumes a high-spin state with a local moment of about 3 mu(B). In the bulk, the interaction between these local moments is very short ranged and the antiferromagnetic (AFM) ordering is energetically more favorable. The formation of V-V-Mg-V defect clusters is found to weaken the antiferromagnetic coupling in bulk MgO, degenerating the AFM and ferro-magnetic state. However, these clusters are high in energy and will not form at equilibrium conditions. By employing the GGA+U approach, with U=5 eV, the V 3d states on the (001) surface are shifted below the Fermi level, and a reasonable surface geometry was achieved. A calculation with the hybrid HSE03 functional, contradicts the GGA+U results, indicating that the V-MgO surface should be metallic at this concentration. From the energetics it is concluded that, at the modeled concentration, VxOy phases will limit the solubility of V in MgO at equilibrium conditions, which is in agreement with previous experimental findings. In order to achieve higher concentrations of V, an off-equilibrium synthesis method is needed. Finally, we find that the formation energy of V at the surface is considerably higher than in the bulk and V is thus expected to diffuse from the surface into the bulk of MgO.

  • 457.
    Århammar, Cecilia
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Moysés Araújo, C.
    Rao, K Venkat.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    First-principles investigation of magnetic properties of V-doped MgO: bulk and (001) surfaceManuskript (Övrigt vetenskapligt)
  • 458.
    Århammar, Cecilia
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Pietzsch, Annette
    Bock, Nicolas
    Holmstroem, Erik
    Araujo, C. Moyses
    Grasjo, Johan
    Zhao, Shuxi
    Green, Sara
    Peery, T.
    Hennies, Franz
    Amerioun, Shahrad
    Foehlisch, Alexander
    Schlappa, Justine
    Schmitt, Thorsten
    Strocov, Vladimir N.
    Niklasson, Gunnar A.
    Wallace, Duane C.
    Rubensson, Jan-Erik
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Unveiling the complex electronic structure of amorphous metal oxides2011Ingår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 108, nr 16, s. 6355-6360Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Amorphous materials represent a large and important emerging area of material's science. Amorphous oxides are key technological oxides in applications such as a gate dielectric in Complementary metal-oxide semiconductor devices and in Silicon-Oxide-Nitride-Oxide-Silicon and TANOS (TaN-Al2O3-Si3N4-SiO2-Silicon) flash memories. These technologies are required for the high packing density of today's integrated circuits. Therefore the investigation of defect states in these structures is crucial. In this work we present X-ray synchrotron measurements, with an energy resolution which is about 5-10 times higher than is attainable with standard spectrometers, of amorphous alumina. We demonstrate that our experimental results are in agreement with calculated spectra of amorphous alumina which we have generated by stochastic quenching. This first principles method, which we have recently developed, is found to be superior to molecular dynamics in simulating the rapid gas to solid transition that takes place as this material is deposited for thin film applications. We detect and analyze in detail states in the band gap that originate from oxygen pairs. Similar states were previously found in amorphous alumina by other spectroscopic methods and were assigned to oxygen vacancies claimed to act mutually as electron and hole traps. The oxygen pairs which we probe in this work act as hole traps only and will influence the information retention in electronic devices. In amorphous silica oxygen pairs have already been found, thus they may be a feature which is characteristic also of other amorphous metal oxides.

78910 451 - 458 av 458
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