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  • 1. Al-Zoubi, N.
    et al.
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Assessing the Exact Muffin-Tin Orbitals method for the Bain path of metals2017Ingår i: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 97, nr 15, s. 1243-1264Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We scrutinise the muffin-tin approximation and the screening within the framework of the Exact Muffin-Tin Orbitals method in the case of cubic and tetragonal crystal symmetries. Systematic total energy calculations are carried out for the Bain path including the body-centred cubic and face-centred cubic structures for a set of simple and transition metals. The present converged results in terms of potential sphere radius (S) and hard sphere radius (b) are in good agreement with previous theoretical calculations. We demonstrate that for all structures considered here, potential sphere radii around and slightly larger than the average Wigner–Seitz radius (w) yield accurate total energy results whereas S values smaller than w give large errors. It is shown that for converged total energies hard spheres with radii b = 0.7–0.8w should be used for an efficient screening within real space clusters consisting typically of 70–90 lattice sites. The less efficient convergence of the total energy in the case of small hard spheres is ascribed to the delocalisation of the screened spherical waves, which leads to inaccurate interstitial overlap matrix. The above conclusions are not significantly affected by the volume of the system.

  • 2.
    Al-Zoubi, Noura
    et al.
    Tafila Tech Univ, Dept Appl Phys, Tafila, Jordan..
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Xiaoqing
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Elastic properties of 4d transition metal alloys: Values and trends2019Ingår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 159, s. 273-280Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using the Exact Muffin-Tin Orbitals method within the Perdew-Burke-Ernzerhof exchange-correlation approximation for solids and solid surfaces (PBEso1), we study the single crystal elastic constants of 4d transition metals (atomic number Z between 39 and 47) and their binary alloys in the body centered cubic (bcc) and face centered cubic (fcc) structures. Alloys between the first neighbors Z(Z + 1) and between the second neighbors Z(Z + 2) are considered. The lattice constants, bulk moduli and elastic constants are found in good agreement with the available experimental and theoretical data. It is shown that the correlation between the relative tetragonal shear elastic constant C-fcc'-2C(bcc)' and the structural energy difference between the fcc and bcc lattices Delta E is superior to the previously considered models. For a given crystal structure, the equiatomic Z(Z + 2) alloys turn out to have similar structural and elastic properties as the pure elements with atomic number (Z + 1). Furthermore, alloys with composition Z(1-x)(Z + 2)(x) possess similar properties as Z(1-2x)(Z + 1)(2x). The present theoretical data on the structural and the elastic properties of 4d transition metal alloys provides consistent input for coarse scale modeling of material properties.

  • 3. Csire, Gabor
    et al.
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ujfalussy, Balazs
    First-principles approach to thin superconducting slabs and heterostructures2016Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, nr 14, artikel-id 140502Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a fully first-principles method for superconducting thin films. The layer dependent phonon spectrum is calculated to determine the layer dependence of the electron-phonon coupling for such systems, which is coupled to the Kohn-Sham-Bogoliubov-de Gennes equations, and it is solved in a parameter-free way. The theory is then applied to different surface facets of niobium slabs and to niobium-gold heterostructures. We investigate the dependence of the transition temperature on the thickness of the slabs and the inverse proximity effect observed in thin superconducting heterostructures.

  • 4.
    Dong, Zhihua
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Chen, D.
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Long, M.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Longitudinal spin fluctuation contribution to thermal lattice expansion of paramagnetic Fe2017Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 95, nr 5, artikel-id 054426Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using an efficient first-principles computational scheme for paramagnetic body-centered cubic (bcc) and face-centered cubic (fcc) Fe, we investigate the impact of thermal longitudinal spin fluctuations (LSFs) on the thermal lattice expansion. The equilibrium physical parameters are derived from the self-consistent Helmholtz free energy, in which the LSFs are considered within the adiabatic approximation and the anharmonic lattice vibration effect is included using the Debye-Grüneisen model taking into account the interplay between thermal, magnetic, and elastic degrees of freedom. Thermal LSFs are energetically more favorable in the fcc phase than in the bcc one giving a sizable contribution to the linear thermal expansion of γ-Fe. The present scheme leads to accurate temperature-dependent equilibrium Wigner-Seitz radius, bulk modulus, and Debye temperature within the stability fields of the two phases and demonstrates the importance of thermal spin fluctuations in paramagnetic Fe.

  • 5.
    Dong, Zhihua
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Chongqing University, China.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Lu, Song
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Chen, Dengfu
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden; Wigner Research Center for Physics, Hungary.
    Thermal spin fluctuation effect on the elastic constants of paramagnetic Fe from first principles2015Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, nr 22, artikel-id 224420Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate the impact of longitudinal thermal spin fluctuations on the temperature dependence of the elastic constants of paramagnetic body-centered-cubic (bcc) and face-centered-cubic (fcc) Fe. Based on a series of constrained local magnetic moment calculations, the spin fluctuation distribution is established using Boltzmann statistics and involving the Jacobian weight, and a temperature-dependent quadratic mean moment is introduced that accurately represents the spin fluctuation state as a function of temperature. We show that with increasing temperature, c' and c(44) for the fcc phase and c(44) for the bcc phase decrease at different rates due to different magnetoelastic coupling strengths. In contrast, c' in the bcc phase exhibits relatively high thermal stability. Longitudinal thermal spin fluctuations diminish the softening of both elastic constants in either phase and have comparatively large contributions in the fcc phase. In both bcc and fcc Fe, c(44) has a larger temperature factor than c'. On the other hand, c' is more sensitive to the longitudinal thermal spin fluctuations, which balance the volume-induced softening by 21.6% in fcc Fe.

  • 6.
    Dong, Zhihua
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Chen, Dengfu
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Long, Mujun
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Uppsala, Sweden; Research Institute for Solid State Physics and Optics, Wigner Research Center for Physics, Budapest, Hungary.
    Elastic properties of paramagnetic austenitic steel at finite temperature: Longitudinal spin fluctuations in multicomponent alloys2017Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, nr 17, artikel-id 174415Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We propose a first-principles framework for longitudinal spin fluctuations (LSFs) in disordered paramagnetic (PM) multicomponent alloy systems and apply it to investigate the influence of LSFs on the temperature dependence of two elastic constants of PM austenitic stainless steel Fe15Cr15Ni. The magnetic model considers individual fluctuating moments in a static PM medium with first-principles-derived LSF energetics in conjunction with describing chemical disorder and randomness of the transverse magnetic component in the single-site alloy formalism and disordered local moment (DLM) picture. A temperature-sensitive mean magnetic moment is adopted to accurately represent the LSF state in the elastic-constant calculations. We make evident that magnetic interactions between an LSF impurity and the PM medium are weak in the present steel alloy. This allows gaining accurate LSF energetics and mean magnetic moments already through a perturbation from the static DLM moments instead of a tedious self-consistent procedure. We find that LSFs systematically lower the cubic shear elastic constants c' and c(44) by similar to 6 GPa in the temperature interval 300-1600 K, whereas the predominant mechanism for the softening of both elastic constants with temperature is the magneto-volume coupling due to thermal lattice expansion. We find that non-negligible local magnetic moments of Cr and Ni are thermally induced by LSFs, but they exert only a small influence on the elastic properties. The proposed framework exhibits high flexibility in accurately accounting for finite-temperature magnetism and its impact on the mechanical properties of PM multicomponent alloys.

  • 7.
    Dong, Zhihua
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Chen, Dengfu
    Chongqing Univ, Coll Mat Sci & Engn, Chongqing 400030, Peoples R China..
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Thermal spin fluctuations in CoCrFeMnNi high entropy alloy2018Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, artikel-id 12211Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    High entropy alloys based on 3d transition metals display rich and promising magnetic characteristics for various high-technology applications. Understanding their behavior at finite temperature is, however, limited by the incomplete experimental data for single-phase alloys. Here we use first-principles alloy theory to investigate the magnetic structure of polymorphic CoCrFeMnNi in the paramagnetic state by accounting for the longitudinal spin fluctuations (LSFs) as a function of temperature. In both face-centered cubic (fcc) and hexagonal close-packed (hcp) structures, the LSFs induce sizable magnetic moments for Co, Cr and Ni. The impact of LSFs is demonstrated on the phase stability, stacking fault energy and the fcc-hcp interfacial energy. The hcp phase is energetically preferable to the fcc one at cryogenic temperatures, which results in negative stacking fault energy at these conditions. With increasing temperature, the stacking fault energy increases, suppressing the formation of stacking faults and nano-twins. Our predictions are consistent with recent experimental findings.

  • 8.
    Dong, Zhihua
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kwon, Se Kyun
    Pohang Univ Sci & Technol, Grad Inst Ferrous Technol, Pohang 37673, South Korea..
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala Univ, Div Mat Theory, Dept Phys & Astron, SE-75121 Uppsala, Sweden.;Wigner Res Ctr Phys, Res Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary..
    Plastic deformation modes in paramagnetic gamma-Fe from longitudinal spin fluctuation theory2018Ingår i: International journal of plasticity, ISSN 0749-6419, E-ISSN 1879-2154, Vol. 109, s. 43-53Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using an efficient first-principles computational scheme, we calculate the intrinsic stacking fault energy (gamma(isf) ) and the unstable stacking fault energy (gamma(usf)) of paramagnetic gamma-Fe as a function of temperature. The formation energies are derived from free energies accounting for thermal longitudinal spin fluctuations (LSFs). LSFs are demonstrated to be important for the accurate description of the temperature-dependent magnetism, intrinsic and unstable stacking fault energies, and have a comparatively large effect on gamma(isf) of gamma-Fe. Dominated by the magneto-volume coupling at thermal excitations, gamma(isf) of gamma-Fe exhibits a positive correlation with temperature, while gamma(usf )declines with increasing temperature. The predicted stacking fault energy of gamma-Fe is negative at static condition, crosses zero around 540 K, and reaches 71.0 mJ m(-2) at 1373 K, which is in good agreement with the experimental value. According to the plasticity theory formulated in terms of the intrinsic and unstable stacking fault energies, twinning remains a possible deformation mode even at elevated temperatures. Both the large positive temperature slope of gamma(usf) and the predicted high-temperature twinning are observed in the case of austenitic stainless steels.

  • 9.
    Huang, Shuo
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Xiaoqing
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Bergqvist, Lars
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Holmström, E.
    Varga, L. K.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Wigner Research Centre for Physics, Hungary; Uppsala University, Sweden.
    Mechanism of magnetic transition in FeCrCoNi-based high entropy alloys2016Ingår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 103, s. 71-74Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    First-principles alloy theory and Monte-Carlo simulations are performed to investigate the magnetic properties of FeCrCoNiAlx high entropy alloys. Results show that face-centered-cubic (fcc) and body-centered-cubic (bcc) structures possess significantly different magnetic behaviors uncovering that the alloy's Curie temperature is controlled by the stability of the Al-induced single phase or fcc-bcc dual-phase. We show that the appearance of the bcc phase with increasing Al content brings about the observed transition from the paramagnetic state for FeCrCoNi to the ferromagnetic state for FeCrCoNiAl at room-temperature. Similar mechanism is predicted to give rise to room-temperature ferromagnetism in FeCrCoNiGa high entropy alloy.

  • 10.
    Khasanov, Rustem
    et al.
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland..
    Luetkens, Hubertus
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland..
    Morenzoni, Elvezio
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland..
    Simutis, Gediminas
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland..
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Östlin, Andreas
    Univ Augsburg, Augsburg Ctr Innovat Technol, D-86135 Augsburg, Germany.;Univ Augsburg, Ctr Elect Correlat & Magnetism, Theoret Phys 3, Inst Phys, D-86135 Augsburg, Germany..
    Chioncel, Liviu
    Univ Augsburg, Augsburg Ctr Innovat Technol, D-86135 Augsburg, Germany.;Univ Augsburg, Ctr Elect Correlat & Magnetism, Theoret Phys 3, Inst Phys, D-86135 Augsburg, Germany..
    Amato, Alex
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland..
    Superconductivity of Bi-III phase of elemental bismuth: Insights from muon-spin rotation and density functional theory2018Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, nr 14, artikel-id 140504Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using muon-spin rotation the pressure-induced superconductivity in the Bi-III phase of elemental bismuth (transition temperature T-c similar or equal to 7.05 K) was investigated. A Ginzburg-Landau parameter kappa = lambda/xi = 30(6) (lambda is the magnetic penetration depth, xi is the coherence length) was estimated, which turns out to be the highest among known single element superconductors. The temperature dependence of the superconducting energy gap [Delta(T)] reconstructed from lambda(-2)(T) deviates from the weakly coupled BCS prediction. The coupling strength 2 Delta/k(B)T

  • 11.
    Khasanov, Rustem
    et al.
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland..
    Radonjic, Milos M.
    Univ Belgrade, Inst Phys Belgrade, Sci Comp Lab, Ctr Study Complex Syst, Pregrev 118, Belgrade 11080, Serbia..
    Luetkens, Hubertus
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland..
    Morenzoni, Elvezio
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland..
    Simutis, Gediminas
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland..
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Appelt, Wilhelm H.
    Univ Augsburg, Inst Phys, Augsburg Ctr Innovat Technol, Theoret Phys 3, D-86135 Augsburg, Germany.;Univ Augsburg, Inst Phys, Ctr Elect Correlat & Magnetism, Theoret Phys 3, D-86135 Augsburg, Germany..
    Oestlin, Andreas
    Univ Augsburg, Inst Phys, Augsburg Ctr Innovat Technol, Theoret Phys 3, D-86135 Augsburg, Germany.;Univ Augsburg, Inst Phys, Ctr Elect Correlat & Magnetism, Theoret Phys 3, D-86135 Augsburg, Germany..
    Chioncel, Liviu
    Univ Augsburg, Inst Phys, Augsburg Ctr Innovat Technol, Theoret Phys 3, D-86135 Augsburg, Germany.;Univ Augsburg, Inst Phys, Ctr Elect Correlat & Magnetism, Theoret Phys 3, D-86135 Augsburg, Germany..
    Amato, Alex
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland..
    Superconducting nature of the Bi-II phase of elemental bismuth2019Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, nr 17, artikel-id 174506Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The superconductivity in the Bi-II phase of elemental bismuth (transition temperature T-c similar or equal to 3.92 K at pressure p similar or equal to 2.80 GPa) was studied experimentally by means of the muon-spin rotation as well as theoretically by using the Eliashberg theory in combination with density functional theory calculations. Experiments reveal that Bi-II is a type-I superconductor with a zero temperature value of the thermodynamic critical field B-c(0) similar or equal to 31.97 mT. The Eliashberg theory approach provides a good agreement with the experimental T-c and the temperature evolution of B-c . The estimated value for the retardation (coupling) parameter k(B)T(c)/omega(In) approximate to 0.07 (omega(In) is the logarithmically averaged phonon frequency) suggests that Bi-II is an intermediately coupled superconductor.

  • 12. Lee, J. -Y
    et al.
    Punkkinen, M. P. J.
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Nabi, Z.
    Kádas, K.
    Zólyomi, V.
    Koo, Y. M.
    Hu, Q. -M
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Box 516, Uppsala, Sweden.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Box 516, Uppsala, Sweden.
    Kollár, J.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kwon, S. K.
    The surface energy and stress of metals2018Ingår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 674, s. 51-68Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigated surface properties of metals by performing first-principles calculations. A systematic database was established for the surface relaxation, surface energy (γ), and surface stress (τ) for metallic elements in the periodic table. The surfaces were modeled by multi-layered slab structures along the direction of low-index surfaces. The surface energy γ of simple metals decreases as the atomic number increases in a given group, while the surface stress τ has its minimum in the middle. The transition metal series show parabolic trends for both γ and τ with a dip in the middle. The dip occurs at half-band filling due to a long-range Friedel oscillation of the surface charge density, which induces a strong stability to the Peierls-like transition. In addition, due to magnetic effects, the dips in the 3d metal series are shallower and deeper for γ and τ, respectively, than those of the 4d and 5d metals. The surface stress of the transition metals is typically positive, only Cr and Mn have a negative τ for the (100) surface facet, indicating that they are under compression. The light actinides have an increasing γ trend according to the atomic number. The present work provides a useful and consistent database for the theoretical modelling of surface phenomena.

  • 13.
    Li, Guijiang
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Xiaoqing
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Delczeg-Czirjak, Erna K.
    Kvashnin, Yaroslav O.
    Eriksson, Olle
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden.
    Kinetic arrest induced antiferromagnetic order in hexagonal FeMnP0.75Si0.25 alloy2014Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, nr 26, s. 262405-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The magnetic state of the FeMnP0.75Si0.25 alloy was investigated by first principles calculations. The coexistence of ferromagnetic and antiferromagnetic phases in FeMnP0.75Si0.25 with the same hexagonal crystal structure was revealed. It was found that kinetic arrest during the transition from the high temperature disordered paramagnetic phase to the low temperature ordered ferromagnetic phase results in the intermediate metastable and partially disordered antiferromagnetic phase. We propose that the ratio of the ferromagnetic and antiferromagnetic phases in the FeMnP0.75Si0.25 sample can be tuned by adjusting the kinetic process of atomic diffusion. The investigations suggest that careful control of the kinetic diffusion process provides another tuning parameter to design candidate magnetocaloric materials.

  • 14.
    Li, Ruihuan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Dalian University of Technology, China.
    Lu, Song
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. University of Turku, Finland.
    Kim, Dongyoo
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Zhao, Jijun
    Kwon, Se Kyun
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden.
    Stacking fault energy of face-centered cubic metals: thermodynamic and ab initio approaches2016Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 28, nr 39, artikel-id 395001Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 15.
    Li, Ruihuan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Dalian University of Technology, China.
    Lu, Song
    Kim, Dongyoo
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Zhao, Jijun
    Kwon, Se Kyun
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Stacking fault energy of face-centered cubic metals: thermodynamic andab initio approaches2015Manuskript (preprint) (Övrigt vetenskapligt)
  • 16.
    Li, Xiaojie
    et al.
    Dalian Univ Technol, Minist Educ, Key Lab Mat Modificat Laser Electron & Ion Beams, Dalian 116024, Peoples R China.;KTH Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden..
    Li, Xiaoqing
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Ruihuan
    Changzhou Vocat Inst Mechatron Technol, Inst Mold Technol, Changzhou 213164, Peoples R China..
    Zhao, Jijun
    Dalian Univ Technol, Minist Educ, Key Lab Mat Modificat Laser Electron & Ion Beams, Dalian 116024, Peoples R China..
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala Univ, Div Mat Theory, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden.;Res Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary..
    Understanding the mechanical properties of reduced activation steels2018Ingår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 146, s. 260-272Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Reduced activation ferritic/martensitic (RAFM) steels are structural materials with potential application in Generation-IV fission and fusion reactors. We use density-functional theory to scrutinize the micro-mechanical properties of the main alloy phases of three RAFM steels based on the body-centered cubic FeCrWVMn solid solution. We assess the lattice parameters and elastic properties of ferromagnetic alpha-Fe and Fe91Cr9, which are the main building blocks of the RAFM steels, and present a detailed analysis of the calculated alloying effects of V, Cr, Mn, and W on the mechanical properties of Fe91Cr9. The composition dependence of the elastic parameters is decomposed into electronic and volumetric contributions and studied for alloying levels that cover the typical intervals in RAFM steels. A linear superposition of the individual solute effects on the properties of Fe91Cr9 is shown to provide an excellent approximation for the ab initio values obtained for the RAFM steels. The intrinsic ductility is evaluated through Rice's phenomenological theory using the surface and unstable stacking fault energies, and the predictions are contrasted with those obtained by empirical criteria. Alloying with V or W is found to enhance the ductility, whereas additional Cr or Mn turns the RAFM base alloys more brittle.

  • 17.
    Li, Xiaojie
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Dalian University of Technology, China.
    Schonecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Ruihuan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Xiaoqing
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Wang, Yuanyuan
    Zhao, Jijun
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Department of Physics and Astronomy, Division of Materials Theory, Sweden.
    Vitos, Levente
    Department of Physics and Astronomy, Division of Materials Theory, Sweden; Wigner Research Center for Physics, Hungary.
    Ab initio calculations of mechanical properties of bcc W-Re-Os random alloys: effects of transmutation of W2016Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 28, nr 29, artikel-id 295501Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 18.
    Li, Xiaojie
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Dalian Univ Technol, Minist Educ, Key Lab Mat Modificat Laser Electron & Ion Beams, Dalian 116024, Peoples R China..
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Li, Xiaoqing
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Hao, Shengzhi
    Dalian Univ Technol, Minist Educ, Key Lab Mat Modificat Laser Electron & Ion Beams, Dalian 116024, Peoples R China..
    Zhao, Jijun
    Dalian Univ Technol, Minist Educ, Key Lab Mat Modificat Laser Electron & Ion Beams, Dalian 116024, Peoples R China..
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Uppsala Univ, Div Mat Theory, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Uppsala Univ, Div Mat Theory, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden.;Wigner Res Ctr Phys, Res Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary..
    First-principles study of crystal-face specificity in surface properties of Fe-rich Fe-Cr alloys2019Ingår i: PHYSICAL REVIEW MATERIALS, ISSN 2475-9953, Vol. 3, nr 3, artikel-id 034401Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A density-functional theory investigation of the (100) and (110) surfaces of the body-centered cubic (bcc) Fe1-xbCrxb binary alloys, x(b) <= 15 at.%, is reported. The energies and segregation energies of these surfaces were calculated for chemically homogeneous concentration profiles and for Cr surface contents deviating from the nominal one of the bulk. The implications of these results for the surface alloy phase diagram are discussed. The surface chemistry of Fe-Cr(100) is characterized by a transition from Cr depletion to Cr enrichment in a critical bulk Cr composition window of 6 < x(b) < 9 at.%. In contrast, such threshold behavior of the surface Cr content is absent for Fe-Cr(110) and a nearly homogeneous Cr concentration profile is energetically favorable. The strongly suppressed surface-layer relaxation at both surfaces is shown to be of magnetic origin. The compressive, magnetic contribution to the surface relaxation stress is found to correlate well with the surface magnetic moment squared at both surface terminations. The stability of the Cr surface magnetic moments against bulk Cr content is clarified based on the surface electronic structure.

  • 19.
    Li, Xiaoqing
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden.
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    First-principles prediction of the stacking fault energy of gold at finite temperature2017Ingår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 135, s. 88-95Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The intrinsic stacking fault energy (ISFE) γ is a material parameter fundamental to the discussion of plastic deformation mechanisms in metals. Here, we scrutinize the temperature dependence of the ISFE of Au through accurate first-principles derived Helmholtz free energies employing both the super cell approach and the axial Ising model (AIM). A significant decrease of the ISFE with temperature, −(36–39) % from 0 to 890 K depending on the treatment of thermal expansion, is revealed, which matches the estimate based on the experimental temperature coefficient dγ/dT closely. We make evident that this decrease predominantly originates from the excess vibrational entropy at the stacking fault layer, although the contribution arising from the static lattice expansion compensates it by approximately 60%. Electronic excitations are found to be of minor importance for the ISFE change with temperature. We show that the Debye model in combination with the AIM captures the correct sign but significantly underestimates the magnitude of the vibrational contribution to γ(T). The hexagonal close-packed (hcp) and double hcp structures are established as metastable phases of Au. Our results demonstrate that quantitative agreement with experiments can be obtained if all relevant temperature-induced excitations are considered in first-principles modeling and that the temperature dependence of the ISFE is substantial enough to be taken into account in crystal plasticity modeling.

  • 20.
    Li, Xiaoqing
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Zhao, J.
    Johansson, Börje
    Uppsala University, Sweden.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden; Wigner Research Center for Physics, Hungary.
    Alloying effect on the ideal tensile strength of ferromagnetic and paramagnetic bcc iron2016Ingår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 676, s. 565-574Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using ab initio alloy theory formulated within the exact muffin-tin orbitals theory in combination with the coherent potential approximation, we investigate the ideal tensile strength (ITS) in the [001] direction of bcc ferro-/ferrimagnetic (FFM) and paramagnetic (PM) Fe1-xMx (M = Al, V, Cr, Mn, Co, or Ni) random alloys. The ITS of ferromagnetic (FM) Fe is calculated to be 12.6 GPa, in agreement with available data, while the PM phase turns out to posses a significantly lower value of 0.7 GPa. Alloyed to the FM matrix, we predict that V, Cr, and Co increase the ITS of Fe, while Al and Ni decrease it. Manganese yields a weak non-monotonic alloying behavior. In comparison to FM Fe, the alloying effect of Al and Co to PM Fe is reversed and the relative magnitude of the ITS can be altered more strongly for any of the solutes. All considered binaries are intrinsically brittle and fail by cleavage of the (001) planes under uniaxial tensile loading in both magnetic phases. We show that the previously established ITS model based on structural energy differences proves successful in the PM Fe-alloys but is of limited use in the case of the FFM Fe-based alloys. The different performance is attributed to the specific interplay between magnetism and volume change in response to uniaxial tension. We establish a strong correlation between the compositional effect on the ITS and the one on the shear elastic constant C' for the PM Fe-alloys and briefly discuss the relation between hardenability and the ITS.

  • 21.
    Li, Xiaoqing
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Zhao, Jijun
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden;.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden; Wigner Research Center for Physics, Hungary.
    Anomalous ideal tensile strength of ferromagnetic Fe and Fe-rich alloys2014Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, nr 2Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Within the same failure mode, iron has the lowest ideal tensile strength among the transition metals crystallizing in the body-centered cubic structure. Here, we demonstrate that this anomalously low strength of Fe originates partly from magnetism and is reflected in unexpected alloying effects in dilute Fe(M) (M = Al, V, Cr, Mn, Co, Ni) binaries. We employ the structural energy difference and the magnetic pressure to disentangle the magnetic effect on the ideal tensile strength from the chemical effect. We find that the investigated solutes strongly alter the magnetic response of the Fe host from the weak towards a stronger ferromagnetic behavior, which is explained based on single-particle band energies.

  • 22.
    Li, Xiaoqing
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Zhao, Jijun
    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.
    Ideal strength of random alloys from first principles2013Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, nr 21, s. 214203-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The all-electron exact muffin-tin orbitals method in combination with the coherent-potential approximation was employed to investigate the ideal tensile strengths of elemental V and Mo solids, and V-and Mo-based random solid solutions. Under uniaxial [001] tensile loading, the ideal tensile strength of V is 11.6 GPa and the lattice fails by shear. Assuming isotropic Poisson contraction, the ideal tensile strengths are 26.7 and 37.6 GPa for V in the [111] and [110] directions, respectively. The ideal strength of Mo is 26.7 GPa in the [001] direction and decreases when a few percent of Tc is introduced in Mo. For the V-based alloys, Cr increases and Ti decreases the ideal tensile strength in all principal directions. Adding the same concentration of Cr and Ti to V leads to ternary alloys with similar ideal strength values as that of pure V. The alloying effects on the ideal strength are explained using the electronic band structure.

  • 23.
    Li, Xiaoqing
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Zhao, Jijun
    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.
    Ieal tensile strength of ferromagnetic Fe-based alloys from first-principles theoryManuskript (preprint) (Övrigt vetenskapligt)
  • 24. Li, Xiaoqing
    et al.
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Zhao, Jijun
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Elastic anharmonicity of bcc Fe and Fe-based random alloys from first-principles calculations2017Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, nr 2, artikel-id 024203Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We systematically investigate elastic anharmonic behavior in ferromagnetic body-centered cubic (bcc) Fe and Fe1-xMx (M = Al, V, Cr, Co, or Ni) random alloys by means of density-functional simulations. To benchmark computational accuracy, three ab initio codes are used to obtain the complete set of second-and third-order elastic constants (TOECs) for bcc Fe. The TOECs of Fe1-xMx alloys are studied employing the first-principles alloy theory formulated within the exact muffin-tin orbital method in combination with the coherent-potential approximation. It is found that the alloying effects on C-111, C-112, and C-123, which are governed by normal strains only, are more pronounced than those on C-144, C-166, and C-456, which involve shear strains. Remarkably, the magnitudes of all TOECs but C-123 decrease upon alloying with Al, V, Cr, Co, or Ni. Using the computed TOECs, we study compositional effects on the pressure derivatives of the effective elastic constants (dB(ij)/dP), bulk (dK/dP), and shear moduli (dG/dP) and derive longitudinal acoustic nonlinearity parameters (beta). Our predictions show that the pressure derivatives of K and G decrease with x for all solute elements and reveal a strong correlation between the compositional trends on dK/dP and dG/dP arising from the fact that alloying predominantly altersdB(11)/dP. The sensitivity of dB(11)/dP to composition is attributed to intrinsic alloying effects as opposed to lattice parameter changes accompanying solute addition. For Fe and the considered Fe-based alloys, beta along high-symmetry directions orders as beta[111] > beta[100] > beta[110], and alloying increases the directional anisotropy of beta but reduces its magnitude.

  • 25.
    Li, Xiaoqing
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Tian, Fuyang
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. University of Science and Technology Beijing, China.
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Zhao, Jijun
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Uppsala University, Sweden; Wigner Research Center for Physics, Hungary.
    Ab initio-predicted micro-mechanical performance of refractory high-entropy alloys2015Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, artikel-id 12334Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Recently developed high-entropy alloys (HEAs) consisting of multiple principal elements represent a new field of metallurgy and have demonstrated appealing properties for a wide range of applications. Using ab initio alloy theory, we reveal the alloying effect on the elastic properties and the ideal tensile strength (ITS) in the [001] direction of four body-centered cubic (bcc) refractory HEAs based on Zr, V, Ti, Nb, and Hf. We find that these HEAs show high elastic anisotropy and large positive Cauchy pressure, suggesting good extrinsic ductility. Starting from ZrNbHf, it is found that the ITS decreases with equimolar Ti addition. On the other hand, if both Ti and V are added to ZrNbHf, the ITS is enhanced by about 42%. An even more captivating effect is the ITS increase by about 170%, if Ti and V are substituted for Hf. The alloying effect on the ITS is explained by the d-band filling. An intrinsic brittle-to-ductile transition is found in terms of the failure mode under uniaxial tension. These investigations suggest that intrinsically ductile HEAs with high ideal strength can be achieved by controlling the proportion of group four elements to group five elements.

  • 26.
    Schoenecker, Stephan
    et al.
    KTH, Skolan för industriell teknik och management (ITM).
    Li, Xiaoqing
    Koepernik, Klaus
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM).
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM).
    Richter, Manuel
    Metastable cubic and tetragonal phases of transition metals predicted by density-functional theory2015Ingår i: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 5, nr 85, s. 69680-69689Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    By means of density-functional calculations, we systematically investigated 24 transition metals for possible metastable phases in body-centered tetragonal structure (bct), including face-centered cubic (fcc) and body-centered cubic (bcc) geometries. A total of 36 structures not coinciding with equilibrium phases were found to minimize the total energy for the bct degrees of freedom. Among these, the fcc structures of Sc, Ti, Co, Y, Zr, Tc, Ru, Hf, Re, and Os, and bct Zr with c/a = 0.82 were found to be metastable according to their computed phonon spectra. Eight of these predicted phases are not known from the respective pressure-temperature phase diagrams. Possible ways to stabilize the predicted metastable phases are illustrated.

  • 27.
    Schönecker, Stephan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kwon, S. K.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Division of Materials Theory, Uppsala University.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Division of Materials Theory, Uppsala University.
    Surface parameters of ferritic iron-rich Fe-Cr alloy2013Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 25, nr 30, s. 305002-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using first-principles density functional theory in the implementation of the exact muffin-tin orbitals method and the coherent potential approximation, we studied the surface energy and the surface stress of the thermodynamically most stable surface facet (100) of the homogeneous disordered body-centred cubic iron-chromium system in the concentration interval up to 20 at.% Cr. For the low-index surface facets of Fe and Cr, the surface energy of Cr is slightly larger than that of Fe, while the surface stress of Cr is considerably smaller than that of Fe. We find that Cr addition to Fe generally increases the surface energy of the Fe-Cr alloy; however, an increase of the bulk amount of Cr also increases the surface stress. As a result of this unexpected trend, the (100) surface of Fe-Cr becomes more stable against reconstruction with increasing Cr concentration. We show that the observed trends are of magnetic origin. In addition to the homogeneous alloy case, we also investigated the impact of surface segregation on both surface parameters.

  • 28.
    Schönecker, Stephan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Xiaoqing
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kwon, Se Kyun
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Thermal surface free energy and stress of iron2015Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, artikel-id 14860Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Absolute values of surface energy and surface stress of solids are hardly accessible by experiment. Here, we investigate the temperature dependence of both parameters for the (001) and (110) surface facets of body-centered cubic Fe from first-principles modeling taking into account vibrational, electronic, and magnetic degrees of freedom. The monotonic decrease of the surface energies of both facets with increasing temperature is mostly due to lattice vibrations and magnetic disorder. The surface stresses exhibit nonmonotonic behaviors resulting in a strongly temperature dependent excess surface stress and surface stress anisotropy.

  • 29.
    Schönecker, Stephan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Xiaoqing
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden; Wigner Research Center for Physics, Hungary.
    Atomic long-range order effects on Curie temperature and adiabatic spin-wave dynamics in strained Fe-Co alloy films2016Ingår i: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 94, nr 6, artikel-id 064410Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The strained Fe-Co alloy in body-centered tetragonal (bct) structure has raised considerable interest due to its giant uniaxial magnetocrystalline anisotropy energy. On the basis of the classical Heisenberg Hamiltonian with ab initio interatomic exchange interactions, we perform a theoretical study of fundamental finite temperature magnetic properties of Fe1-xCox alloy films as a function of three variables: chemical composition 0.3 <= x <= 0.8, bct geometry [a, c(a)] arising from in-plane strain and associated out-of-plane relaxation, and atomic long-range order (ALRO). The Curie temperatures T-C(x, a) obtained from Monte Carlo simulations display a competition between a pronounced dependence on tetragonality, strong ferromagnetism in the Co-rich alloy, and the beginning instability of ferromagnetic order in the Fe-rich alloy when c/a -> root 2. Atomic ordering enhances T-C and arises mainly due to different distributions of atoms in neighboring coordination shells rather than altering exchange interactions significantly. We investigate the ordering effect on the shape of the adiabatic spin-wave spectrum for selected pairs (x, a). Our results indicate that long-wavelength acoustic spin-wave excitations show dependencies on x, a, and ALRO similar to those of T-C. The directional anisotropy of the spin-wave stiffness d(x, a) peaks in narrow ranges of composition and tetragonality. ALRO exhibits a strong effect on d for near equiconcentration Fe-Co. We also discuss our findings in the context of employing Fe-Co as perpendicular magnetic recording medium.

  • 30.
    Schönecker, Stephan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Xiaoqing
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Richter, Manuel
    IFW Dresden, D-01069 Dresden, Germany.;Dresden Ctr Computat Mat Sci, D-01069 Dresden, Germany..
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Lattice dynamics and metastability of fcc metals in the hcp structure and the crucial role of spin-orbit coupling in platinum2018Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, nr 22, artikel-id 224305Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate the lattice dynamical properties of Ni, Cu, Rh, Pd, Ag, Ir, Pt, and Au in the nonequilibrium hcp structure by means of density-functional simulations, wherein spin-orbit coupling (SOC) was considered for Ir, Pt, and Au. The determined dynamical properties reveal that all eight elements possess a metastable hcp phase at zero temperature and pressure. The hcp Ni, Cu, Rh, Pd, and Au previously observed in nanostructures support this finding. We make evident that the inclusion of SOC is mandatory for an accurate description of the phonon dispersion relations and dynamical stability of hcp Pt. The underlying sensitivity of the interatomic force constants is ascribed to a SOC-induced splitting of degenerate band states accompanied by a pronounced reduction of electronic density of states at the Fermi level. To give further insight into the importance of SOC in Pt, we (i) focus on phase stability and examine a lattice transformation related to optical phonons in the hcp phase and (ii) focus on the generalized stacking fault energy (GSFE) of the fcc phase pertinent to crystal plasticity. We show that the intrinsic stable and unstable fault energies of the GSFE scale as in other common fcc metals, provided that the spin-orbit interaction is taken into account.

  • 31.
    Schönecker, Stephan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. IFW Dresden, Germany.
    Richter, M.
    Koepernik, K.
    Eschrig, H.
    Prediction of first-order martensitic transitions in strained epitaxial films2015Ingår i: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 17, artikel-id 023005Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Coherent epitaxial growth allows us to produce strained crystalline films with structures that are unstable in the bulk. Thereby, the overlayer lattice parameters in the interface plane, (a, b), determine the minimum-energy out-of-plane lattice parameter, cmin(a, b). We show by means of density-functional total energy calculations that this dependence can be discontinuous and predict related first-order phase transitions in strained tetragonal films of the elements V, Nb, Ru, La, Os, and Ir. The abrupt change of cmin can be exploited to switch properties specific to the overlayer material. This is demonstrated for the example of the superconducting critical temperature of a vanadium film which we predict to jump by 20% at a discontinuity of cmin.

  • 32.
    Wang, Guisheng
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Hertzman, Staffan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Termodynamisk modellering.
    Hu, Qing-Miao
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kwon, Se Kyun
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ab initio prediction of the mechanical properties of alloys: The case of Ni/Mn-doped ferromagnetic Fe2015Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, nr 22, s. 224203-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    First-principles alloy theory, formulated within the exact muffin-tin orbitals method in combination with the coherent-potential approximation, is used to study the mechanical properties of ferromagnetic body-centered cubic (bcc) Fe1−xMx alloys (M=Mn or Ni, 0≤x≤0.1). We consider several physical parameters accessible from \emph{ab initio} calculations and their combinations in various phenomenological models to compare the effect of Mn and Ni on the properties of Fe. Alloying is found to slightly alter the lattice parameters and produce noticeable influence on elastic moduli. Both Mn and Ni decrease the surface energy and the unstable stacking fault energy associated with the {110} surface facet and the {110}⟨111⟩ slip system, respectively. Nickel is found to produce larger effect on the planar fault energies than Mn. The semi-empirical ductility criteria by Rice and Pugh consistently predict that Ni enhances the ductility of Fe but give contradictory results in the case of Mn doping. The origin of the discrepancy between the two criteria is discussed and an alternative measure of the ductile-brittle behavior based on the theoretical cleavage strength and single-crystal shear modulus G{110}⟨111⟩ is proposed.

  • 33.
    Wang, Guisheng
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Theory of unstable stacking fault energy of transition metalsManuskript (preprint) (Övrigt vetenskapligt)
  • 34. Wolter, A. U. B.
    et al.
    Corredor, L. T.
    Janssen, L.
    Nenkov, K.
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Do, S. -H
    Choi, K. -Y
    Albrecht, R.
    Hunger, J.
    Doert, T.
    Vojta, M.
    Buechner, B.
    Field-induced quantum criticality in the Kitaev system alpha-RuCl32017Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, nr 4, artikel-id 041405Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    alpha-magnetic excitations akin to Kitaev's honeycomb-lattice spin liquid. We have performed a detailed specific-heat investigation at temperatures down to 0.4 K in applied magnetic fields up to 9 T for fields parallel to the ab plane. We find a suppression of the zero-field antiferromagnetic order, together with an increase of the low-temperature specific heat, with increasing field up to mu H-0(c) approximate to 6.9 T. Above H-c, the magnetic contribution to the low-temperature specific heat is strongly suppressed, implying the opening of a spin-excitation gap. Our data point toward a field-induced quantum critical point at H-c; this is supported by universal scaling behavior near H-c. Remarkably, the data also reveal the existence of a small characteristic energy scale well below 1 meV, above which the excitation spectrum changes qualitatively. We relate the data to theoretical calculations based on a J(1)-K-1-Gamma(1)-J(3) honeycomb model.

  • 35.
    Zhang, Hualei
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Xiaoqing
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Jesperson, Henrik
    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.
    Anomalous elastic hardening in Fe-Co alloys at high temperature2014Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, nr 18, s. 184107-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The elastic moduli of Fe1-cCoc (c <= 0.2) alloys are found to decrease strongly with increasing temperature, but show very weak alloying effects for both low-temperature ferromagnetic and high-temperature paramagnetic states. For temperatures slightly below and around the Curie temperature of Fe, Co addition significantly increases the elastic moduli. The variation of the tetragonal shear elastic constant upon 20% Co addition increases from a small negative value to more than 135% as the temperature rises from 0 to 1200 K. The expected elastic softening in the case of Al doping is not confirmed. Both anomalous trends are ascribed to the interplay between intrinsic chemical effects, magnetism, and temperature.

1 - 35 av 35
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