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  • 201. Gonzalez-Borrero, P. P.
    et al.
    Sato, F.
    Medina, A. N.
    Baesso, M. L.
    Bento, A. C.
    Baldissera, Gustavo
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Niklasson, G. A.
    Granqvist, C. G.
    da Silva, A. F.
    Optical band-gap determination of nanostructured WO3 film2010Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 96, nr 6Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The optical band-gap energy of a nanostructured tungsten trioxide film is determined using the photoacoustic spectroscopy method under continuous light excitation. The mechanism of the photoacoustic signal generation is discussed. The band-gap energy is also computed by other methods. The absorption coefficient as well as the band-gap energy of three different crystal structures of tungsten trioxide is calculated by a first-principles Green's function approach using the projector augmented wave method. The theoretical study indicates that the cubic crystal structure shows good agreement with the experimental data.

  • 202. Gorbatov, O. I.
    et al.
    Korzhavyi, Pavel A.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ruban, Andrei V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Gornostyrev, Yu. N.
    Dependence of vacancy-solute interactions on magnetic state in dilute iron-based alloys2011Inngår i: Solid-Solid Phase Transformations in Inorganic Materials: Part 2 / [ed] Y. Brechet, E. Clouet, A. Deschamps, A. Finel, F. Soisson, Zurich-Durnten, Switzerland: TRANS TECH PUBLICATIONS , 2011, s. 979-984Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Vacancy-solute interactions play a crucial role in diffusion-controlled phase transformations, such as ordering or decomposition, which occur in alloys under heat treatment or under irradiation. The knowledge of these interactions is important for predicting long-term behavior of nuclear materials (such as reactor steels and nuclear-waste containers) under irradiation, as well as for advancing our general understanding of kinetic processes in alloys. Using first-principles calculations based on density functional theory and employing the locally self-consistent Green’s function technique, we develop a database of vacancy-solute interactions in dilute alloys of bcc Fe with 3p (Al, Si, P, S), 3d (Ti – Cu), and 4d (Nb – Ag) elements. Interactions within the first two coordination shells have been computed in the ferromagnetic state as well as in the paramagnetic (disordered local moment) state of the iron matrix. Magnetism is found to have a very strong effect on the vacancy-solute interactions.

  • 203. Gorbatov, O. I.
    et al.
    Korzhavyi, Pavel A.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialteknologi.
    Ruban, Andrei V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Gornostyrev, Yu. N.
    Vacancy-solute interactions in ferromagnetic and paramagnetic bcc iron: Ab initio calculations2011Inngår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 419, nr 1-3, s. 248-255Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Vacancy-solute interactions play a crucial role in diffusion-controlled processes, such as ordering or decomposition, which occur in alloys under heat treatment or under irradiation. Detailed knowledge of these interactions is important for predicting long-term behavior of nuclear materials (such as reactor steels and nuclear-waste containers) as well as for advancing our general understanding of kinetic processes in alloys. Using first-principles calculations based on the density functional theory and employing the locally self-consistent Green's function technique, we develop a database of vacancy-solute interactions in dilute alloys of bcc Fe with 3p (Al, Si, P, S), 3d (Sc-Cu), and 4d (Y-Ag) elements. Unrelaxed interactions within the first three coordination shells have been computed in the ferromagnetic state as well as in the paramagnetic (disordered local moment) state of the iron matrix. Magnetism is found to have a strong effect on the vacancy-solute interactions. Implications of the obtained results for interpreting the effects of vacancy trapping and enhanced impurity diffusion are discussed.

  • 204. Gorbatov, O. I.
    et al.
    Kuznetsov, A. R.
    Gornostyrev, Yu. N.
    Ruban, Andrei V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ershov, N. V.
    Lukshina, V. A.
    Chernenkov, Yu. P.
    Fedorov, V. I.
    Role of Magnetism in the Formation of a Short-Range Order in Iron-Silicon Alloys2011Inngår i: Journal of Experimental and Theoretical Physics, ISSN 1063-7761, E-ISSN 1090-6509, Vol. 112, nr 5, s. 848-859Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The formation of a short-range order in soft magnetic Fe-Si alloys depending on the annealing temperature has been investigated theoretically and experimentally. The B2-type short-range order has been observed in samples quenched from temperatures T > T(C) (where T(C) is the Curie temperature) with the content c(Si) close to the boundary of the two-phase region. Annealing at temperatures T < T(C) for the content c(Si) >= 0.08 leads to an increase in the fraction of regions with the D0(3)-type short-range order. The mechanism of the formation of the short-range order in Fe-Si solid solutions has been analyzed by the Monte Carlo simulation with the ab initio calculated interatomic interaction parameters. It has been shown that the energy of the effective Si-Si interaction in bcc iron strongly depends on the magnetic state of the matrix. As a result, the B2-type short-range order is formed at T > T(C) and is fixed at quenching, whereas the D0(3)-type short-range order is equilibrium in the ferromagnetic state. The results reveal the decisive role of magnetism in the formation of the short-range order in Fe-Si alloys and allow the explanation of the observed structural features of the alloys depending on the composition and temperature.

  • 205. Gorbatov, O. I.
    et al.
    Ruban, Andrei V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Korzhavyi, Pavel A.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Gornostyrev, Yu.N.
    Effect of magnetism on precipitation of Cu in bcc Fe: Ab-initio based modeling2009Inngår i: Scientific basis for nuclear waste management XXXIII, Materials Research Society, 2009, s. 469-476Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Theoretical modeling of the decomposition in bcc Fe-Cu alloys has been performed using a combined approach which includes ab-initio calculations of the effective cluster interactions and statistical-mechanical (Monte Carlo) simulations. We showed that the effective Cu-Cu and Cu-vacancy interactions in the bcc Fe matrix have a strong dependence on the global magnetic state of iron. As a result, all the related thermodynamic properties of the alloys (such as solubility limit and diffusivity) are expected to have a pronounced non-Arrhenius temperature behavior, originated from variation of the global magnetization with temperature. We find that strong Cu-vacancy interactions in the bcc Fe matrix lead to a remarkable effect of vacancies on the Cu precipitation and significantly modify the alloy decomposition kinetics under irradiation.

  • 206. Granas, O.
    et al.
    Korzhavyi, Pavel A.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kissavos, A. E.
    Abrikosov, I. A.
    Theoretical study of the Mo-Ru sigma phase2008Inngår i: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 32, nr 1, s. 171-176Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The thermodynamic properties of the Mo-Ru binary sigma-phase are investigated using a combination of ab initio calculations and CALPHAD modeling. Total energy calculations have been performed for the complete set of 32 end-member compounds of a 5-sublattice compound energy model. The internal crystallographic parameters for each end-member compound have been determined by minimising the total energy. A simpler, 3-sublattice model of the Mo-Ru a-phase is formulated on the basis of calculated total energies. The site occupancy is acquired by minimising the free energy given by the compound energy model. A strong preference of Mo and Ru towards high-coordination sites and icosahedral sites in the Mo-Ru a-phase is found and analysed in terms of the electronic structure.

  • 207. Grechnev, G. E.
    et al.
    Logosha, A. V.
    Svechkarev, I. V.
    Kuchin, A. G.
    Kulikov, Y. A.
    Korzhavyi, Pavel A.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Eriksson, O.
    Electronic structure and magnetic properties of RNi5-xCux alloys (R=Y, La, Ce)2006Inngår i: Low temperature physics (Woodbury, N.Y., Print), ISSN 1063-777X, E-ISSN 1090-6517, Vol. 32, nr 12, s. 1140-1146Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A study is made of the electronic structure and magnetic properties of RN5-xCux alloys (R = Y, La, Ce). The influence of substitution of nickel by copper on the features of the band structure and behavior of the magnetic susceptibility of these alloys is investigated. An analysis is made of the electronic states and interactions responsible for the magnetic properties of RNi5-xCux alloys.

  • 208. Grigoriev, A.
    et al.
    Skorodumova, N. V.
    Simak, S. I.
    Wendin, G.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, R.
    Electron transport in stretched monoatomic gold wires2006Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 97, nr 23Artikkel i tidsskrift (Fagfellevurdert)
  • 209.
    Grönhagen, Karin
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Metallografi.
    Razumowski, Vsevolod
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ödqvist, J.
    Ruban, Andrei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Korzhavyi, Pavel A.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Phase-field coupled with CALPHAD database and ab-initio modeling of diffusion barriers and prefactors for simulating spinodal decomposition in ZrC-TiC carbidesManuskript (preprint) (Annet vitenskapelig)
  • 210. Gubicza, J.
    et al.
    Heczel, A.
    Kawasaki, M.
    Han, J. -K
    Zhao, Y.
    Xue, Y.
    Huang, Shuo
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Lábár, J. L.
    Evolution of microstructure and hardness in Hf 25 Nb 25 Ti 25 Zr 25 high-entropy alloy during high-pressure torsion2019Inngår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 788, s. 318-328Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A four-component equimolar high-entropy alloy (HEA) with the composition of HfNbTiZr and body-centered cubic (bcc) structure was processed by HPT at RT. The evolution of the dislocation density, the grain size and the hardness was monitored along the HPT-processed disk radius for different numbers of turns between ¼ and 20. It was found that most of the increase of the dislocation density and the refinement of the grain structure occurred up to the shear strain of ∼40. Between the strains of ∼40 and ∼700, only a slight grain size reduction was observed. The saturated dislocation density and grain size were ∼2.1 × 10 16 m −2 and ∼30 nm, respectively. The saturation in hardness was obtained at ∼4450 MPa. These values were similar to the parameters determined in the literature for five-component HEAs processed by HPT. The analysis confirmed that the main component in the strength was given by the friction stress in the HPT-processed bcc HfNbTiZr HEA. It was also revealed that the contribution of the high dislocation density to the strength was significantly higher than the effect of the small grain size.

  • 211. Guo, J. H.
    et al.
    Vayssieres, L.
    Persson, Clas
    Ahuja, R.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Nordgren, J.
    Polarization-dependent soft-x-ray absorption of a highly oriented ZnO microrod-array2005Inngår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 17, nr 1, s. 235-240Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Polarization-dependent x-ray absorption measurements were performed on a crystalline ZnO three-dimensional array consisting of highly oriented microrods as well as on particulate thin film consisting of monodisperse spherical nanoparticles. Strong anisotropic effects have been observed for the highly oriented ZnO rods, unlike for the isotropic spherical ones. Full-potential calculations of orbital-resolved x-ray absorption of a ZnO wurtzite periodic crystal, including the Zn 3d as part of the valence states, shows a very good agreement with the experimental findings. Comprehensive fundamental knowledge of the electronic structure of ZnO is obtained by probing and demonstrating the orbital symmetry of oxygen and its contribution to the conduction band of this important II-VI semiconductor.

  • 212. Guo, Z.
    et al.
    Sa, B.
    Pathak, B.
    Zhou, J.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Sun, Z.
    Band gap engineering in huge-gap semiconductor SrZrO3 for visible-light photocatalysis2014Inngår i: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 39, nr 5, s. 2042-2048Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Using SrZrO3 (SZO, the intrinsic band gap being 5.6 eV) as an example, we have investigated the design principles for huge-gap semiconductors with band gap larger than 5 eV for the application of efficient visible-light driven photocatalysts for splitting water into hydrogen. Based on the hybrid density function calculations, the electronic structures of mono-doped and co-doped SZO are investigated to obtain design principles for improving their photocatalytic activity in hydrogen generation. The cationic-anionic co-doping in SZO could reduce the band gap significantly and its electronic band position is excellent for the visible-light photocatalysis. This work reports a new type of candidate material for visible-light driven photocatalysis, i.e., huge-gap semiconductors with band gap larger than 5 eV. Furthermore, based on the present results we have proposed the design principles for band gap engineering that provides general guideline for other huge-gap semiconductors.

  • 213. Han, Sung-Ho
    et al.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Hasoon, Falah S.
    Al-Thani, Hamda A.
    Hermann, Allen M.
    Levi, Dean H.
    Optical properties and electronic structures of (4CuInSe(2))(y)(CuIn5Se8)(1-y)2006Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, nr 8Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Spectroscopic ellipsometric measurements of thin polycrystalline (4CuInSe(2))(y)(CuIn5Se8)(1-y) films reveal that there are important differences in optical properties and electronic structures between alpha-phase CuInSe2 and Cu-poor CuInSe2. We report the optical functions of thin-film polycrystalline (4CuInSe(2))(y)(CuIn5Se8)(1-y) and describe how they change depending on the degree of Cu deficiency. We find a reduction in the absorption strength in the spectral region of 1-3 eV for Cu-poor CuInSe2. This reduction can be explained in terms of density of the Cu 3d states in CuInSe2. Cu-poor CuInSe2 samples show an increase in band gap due to reduced p-d interaction. We find that the reduction in the amplitudes of E-0(A,B,C) transitions at the Gamma point and E-1(A,B) transitions at the N point are due to Cu deficiency. Local density approximation calculations with a modeled on-site self-interaction correction of the absorption coefficients of Cu8In8Se16 (CuInSe2), Cu5In9Se16 (CuIn3Se5-like), and Cu2In10Se16 (CuIn5Se8) are in good agreement with those of thin-film polycrystalline CuInSe2 samples with 24.1, 15.6, and 9.1 at. % Cu, respectively.

  • 214. Han, XJ.
    et al.
    Bergqvist, Lars
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Dederichs, Peter H.
    Muller-Krumbhaar, Heinz
    Christie, Jaime
    Scandolo, Sandro
    Tangney, Paul
    Polarizable interatomic force field for TiO2 parametrized using density functional theory2010Inngår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 81, s. 134108-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report a classical interatomic force field for TiO2, which has been parametrized using density functional theory forces, energies, and stresses in the rutile crystal structure. The reliability of this classical potential is tested by evaluating the structural properties, equation of state, phonon properties, thermal expansion, and some thermodynamic quantities such as entropy, free energy, and specific heat under constant volume. The good agreement of our results with ab initio calculations and with experimental data, indicates that our force field describes the atomic interactions of TiO2 in the rutile structure very well. The force field can also describe the structures of the brookite and anatase crystals with good accuracy.

  • 215. He, Y.
    et al.
    Scheicher, R. H.
    Grigoriev, A.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Uppsala, Sweden .
    Long, S.
    Ji, Z.
    Yu, Z.
    Liu, M.
    Fast DNA sequencing via transverse differential conductance2010Inngår i: SISPAD 2010 - 15th International Conference on Simulation Of Semiconductor Processes and Devices, IEEE , 2010, s. 313-316Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We propose using characteristic transverse differential conductance for solid-state nanopore-based DNA sequencing and have explored this idea by performing molecular dynamics simulations on the translocation progress of single-stranded DNA molecule through the nanopore, and calculating the associated transverse differential conductance. Our results show that measurement of the transverse differential conductance is suitable to successfully discriminate between the four nucleotide types, and we show that this identification could even withstand electrical noise caused by fluctuations due to changes in the DNA orientation. Our findings demonstrate several compelling advantages of the differential conductance approach, which may lead to important applications in rapid genome sequencing.

  • 216. He, Yuhui
    et al.
    Scheicher, Ralph H.
    Grigoriev, Anton
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Long, Shibing
    Huo, ZongLiang
    Liu, Ming
    Enhanced DNA Sequencing Performance Through Edge-Hydrogenation of Graphene Electrodes2011Inngår i: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 21, nr 14, s. 2674-2679Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The use of graphene electrodes with hydrogenated edges for solid-state nanopore-based DNA sequencing is proposed, and molecular dynamics simulations in conjunction with electronic transport calculations are performed to explore the potential merits of this idea. The results of the investigation show that, compared to the unhydrogenated system, edge-hydrogenated graphene electrodes facilitate the temporary formation of H-bonds with suitable atomic sites in the translocating DNA molecule. As a consequence, the average conductivity is drastically raised by about 3 orders of magnitude while exhibiting significantly reduced statistical variance. Furthermore, the effect of the distance between opposing electrodes is investigated and two regimes identified: for narrow electrode separation, the mere hindrance due to the presence of protruding hydrogen atoms in the nanopore is deemed more important, while for wider electrode separation, the formation of H-bonds becomes the dominant effect. Based on these findings, it is concluded that hydrogenation of graphene electrode edges represents a promising approach to reduce the translocation speed of DNA through the nanopore and substantially improve the accuracy of the measurement process for whole-genome sequencing.

  • 217. He, Yuhui
    et al.
    Shao, Lubing
    Scheicher, Ralph H.
    Grigoriev, Anton
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Long, Shibing
    Ji, Zhuoyu
    Yu, Zhaoan
    Liu, Ming
    Differential conductance as a promising approach for rapid DNA sequencing with nanopore-embedded electrodes2010Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 97, nr 4, s. 043701-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We propose an approach for nanopore-based DNA sequencing using characteristic transverse differential conductance. Molecular dynamics and electron transport simulations show that the transverse differential conductance during the translocation of DNA through the nanopore is distinguishable enough for the detection of the base sequence and can withstand electrical noise caused by DNA structure fluctuation. Our findings demonstrate several advantages of the transverse conductance approach, which may lead to important applications in rapid genome sequencing. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3467194]

  • 218. Heathman, S.
    et al.
    Haire, R. G.
    Le Bihan, T.
    Ahuja, R.
    Li, S.
    Luo, W.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    The unique high-pressure behavior of curiurn probed further using alloys2007Inngår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 444, s. 138-141Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The changing role of the 5f electrons across the actinide series has been of prime interest for many years. The remarkable behavior of americium's 5f electrons under pressure was determined experimentally a few years ago and it precipitated a strong interest in the heavy element community. Theoretical treatments of americium's behavior under pressure followed and continue today. Experimental and theoretical findings regarding curium's behavior under pressure have shown that the pressure behavior of curium was not a mirror image of that for americium. Rather, one of the five crystallographic phases observed with curium (versus four for americium) was a unique monoclinic structure whose existence is due to a spin stabilization effect by curium's 5f(7) electronic configuration and its half-filled 5f-shell. We review briefly the behavior of pure curium under pressure but focus on the pressure behaviors of three curium alloys with the intent of comparing them with pure curium. An important experimental finding confirmed by theoretical computations, is that dilution of curium with its near neighbors is sufficient to prevent the formation of the unique C2/c phase that appears in pure Cm metal under pressure. As this unique C2/c phase is very sensitive to having a 5f7 configuration to maximize the magnetic spin polarization, dilution of this state with adjacent actinide neighbors reduces its stability.

  • 219. Heathman, S.
    et al.
    Haire, R. G.
    Le Bihan, T.
    Lindbaum, A.
    Idiri, M.
    Normile, P.
    Li, S.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Lander, G. H.
    A high-pressure structure in curium linked to magnetism2005Inngår i: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 309, nr 5731, s. 110-113Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Curium ties at the center of the actinide series and has a half-filled shell. with seven 5f electrons spatially residing inside its radon core. As a function of pressure, curium exhibits five different crystallographic phases up to 100 gigapascals, of which all but one are also found in the preceding element, americium. We describe here a structure in curium, Cm III, with monoctinic symmetry, space group C2/c, found at intermediate pressures (between 37 and 56 gigapascals). Ab initio electronic structure calculations agree with the observed sequence of structures and establish that it is the spin polarization of curium's 5f electrons that stabilizes Cm Ill. The results reveal that curium is one of a few elements that has a lattice structure stabilized by magnetism.

  • 220. Heathman, S.
    et al.
    Le Bihan, T.
    Yagoubi, S.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Department of Physics and Materials Science, Uppsala University.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Department of Physics and Materials Science, Uppsala University.
    Structural investigation of californium under pressure2013Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, nr 21, s. 214111-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The high-pressure structural behavior of californium has been studied experimentally and theoretically up to 100 GPa. A valence change from divalent to trivalent forms was observed under modest pressure revealing californium to be the only actinide to exhibit more than one metallic valence at near to ambient conditions as is the case for cerium in the lanthanide series. Three metallic valencies and four different crystallographic phases were observed in californium as a function of pressure. High-pressure techniques, synchrotron radiation, and ab initio electronic structure calculations of total energies were used to investigate the material and to determine the role which californium's 5f electrons play in influencing these transitions. The crystallographic structures observed are similar to those found in the preceding actinide elements, curium and americium, with the initially localized 5f states becoming completely delocalized under the influence of high pressure.

  • 221. Heinonen, M. H.
    et al.
    Kokko, K.
    Punkkinen, Marko Patrick John
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Nurmi, E.
    Kollar, J.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Initial Oxidation of Fe-Al and Fe-Cr-Al Alloys: Cr as an Alumina Booster2011Inngår i: Oxidation of Metals, ISSN 0030-770X, E-ISSN 1573-4889, Vol. 76, nr 3-4, s. 331-346Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The boosting effect of Cr on the growth of the protective alumina scale on Fe-Al alloys is investigated by X-ray photoelectron spectroscopy. Using low oxygen pressure the surface chemistry of the alloys is monitored starting from the first moments of oxidation. Chromium affects the Fe/Al surface-bulk exchange which is clearly detected by analyzing the measured surface concentrations within the atomic concentration models. Experimental results presented are in good agreement with the previous ones obtained by experiments at ambient conditions and ab initio calculations.

  • 222. Hellman, O.
    et al.
    Skorodumova, Natalia V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Simak, S. I.
    Charge Redistribution Mechanisms of Ceria Reduction2012Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 108, nr 13, s. 135504-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Charge redistribution at low oxygen vacancy concentrations in ceria have been studied in the framework of the density functional theory. We propose a model to approach the dilute limit using the results of supercell calculations. It allows one to reproduce the characteristic experimentally observed behavior of composition versus oxygen pressure dependency. We show that in the dilute limit the charge redistribution is likely to be driven by a mechanism different from the one involving electron localization on cerium atoms. We demonstrate that it can involve charge localization on light element impurities.

  • 223.
    Hertzman, Staffan N.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Charles, J.
    GM APERAM I R&D, St Denis, France.
    On the effect of nitrogen on duplex stainless steels2011Inngår i: Revue de métallurgie (Imprimé), ISSN 0035-1563, E-ISSN 1156-3141, Vol. 108, nr 7-8, s. 413-425Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    One of the key issues in the development of the modern duplex stainless steels was the introduction of nitrogen as an alloying element. This was made possible by e. g. the AOD process and has meant that the problems with earlier grades regarding weldability could be solved. The prime reason for the lower weldability, namely a coarse-grained heat affected zone with inferior properties was then removed. Further beneficial effects of nitrogen increases in the new generation of duplex grades were pointed out: localized corrosion resistance particularly in chloride containing solutions, enhancement of fatigue properties, improved creep properties particularly when considering heat treatment ... The paper will outline the influence of nitrogen additions in duplex grades by means of thermodynamic calculations including phase diagrams, TTT phase precipitation diagrams from metallographic investigations, mechanical and corrosion properties. Metallographic investigations, corrosion resistance properties and mechanical properties will be presented. The specific links between welded joints microstructures and properties with different nitrogen contents will be discussed.

  • 224. Hoffmann, Martin
    et al.
    Marmodoro, Alberto
    Nurmi, Eero
    Kokko, Kalevi
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ernst, Arthur
    Hergert, Wolfram
    Elastic anomalies and long/short-range ordering effects: A first-principles investigation of the AgcPd1-c solid solution2012Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, nr 9, s. 094106-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We investigate the elastic properties of the binary alloy Ag-Pd. The lattice constant of this system shows significant deviations from the linear behavior anticipated by the semi-empirical Vegard's rule. This effect was formerly studied by assuming total substitutional disorder, and described by the coherent potential approximation (CPA). Theoretical phase diagram investigations have however suggested three ordered phases at low temperatures, and we extend our first-principles investigation to include such scenarios through the adoption of an extended unit cell representation and a recently developed multisublattice generalization of the original CPA. This allows us to explore equilibrium lattice constant and bulk modulus within a unified approach even in the presence of partial long-range order. We obtain significant variations of the bulk modulus in comparison to the totally disordered picture, and again very rich deviations from more intuitive predictions of a simple linear behavior. We follow former suggestions to analyze the different regimes in connection with topological transitions of the Fermi surface, examined through Bloch spectral function calculations.

  • 225. Hoglund, A.
    et al.
    Castleton, C. W. M.
    Göthelid, Mats
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik, Materialfysik, MF.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Mirbt, S.
    Point defects on the (110) surfaces of InP, InAs, and InSb: A comparison with bulk2006Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, nr 7Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The basic properties of point defects, such as local geometries, positions of charge-transfer levels, and formation energies, have been calculated using density-functional theory, both in the bulk and on the (110) surface of InP, InAs, and InSb. Based on these results we discuss the electronic properties of bulk and surface defects, defect segregation, and compensation. In comparing the relative stability of the surface and bulk defects, it is found that the native defects generally have higher formation energies in the bulk. From this it can be concluded that at equilibrium there is a considerably larger fraction of defects at the surface and under nonequilibrium conditions defects are expected to segregate to the surface, given sufficient time. In most cases the charge state of a defect changes upon segregation, altering the charge-carrier concentrations. The photothresholds are also calculated for the three semiconductors and are found to be in good agreement with experimental data.

  • 226. Holmstrom, E.
    et al.
    Olovsson, W.
    Abrikosov, I. A.
    Niklasson, A. M. N.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Gorgoi, M.
    Karis, O.
    Svensson, S.
    Schafers, F.
    Braun, W.
    Ohrwall, G.
    Andersson, G.
    Marcellini, M.
    Eberhardt, W.
    Sample preserving deep interface characterization technique2006Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 97, nr 26Artikkel i tidsskrift (Fagfellevurdert)
  • 227. Hones, K.
    et al.
    Eickenberg, M.
    Siebentritt, S.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Polarization of defect related optical transitions in chalcopyrites2008Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 93, nr 9Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We investigate the symmetry of shallow acceptors in Cu chalcopyrites by polarization dependent photoluminescence measurements and density functional calculations. We determine the influence of the band symmetry versus the site symmetry. The polarization of the emitted or absorbed light is parallel to the c-axis in the case of CuGaSe2 and perpendicular to the c-axis in the case of CuInSe2. The symmetry of the defects depends in each case on the symmetry of the topmost band. Neither does the site symmetry affect the defect symmetry nor do the defects change the symmetry of the band.

  • 228. Hu, Q. M.
    et al.
    Kadas, K.
    Hogmark, S.
    Yang, R.
    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.
    Hardness and elastic properties of covalent/ionic solid solutions from first-principles theory2008Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 103, nr 8Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Most of the engineering materials are alloys (solid solutions) and inevitably contain some impurities or defects such as vacancies. However, theoretical predictions of the hardness of this kind of materials have rarely been addressed in literature. In this paper, a hardness formula for multicomponent covalent solid solution is proposed based on the work of Simunek and Vackar [Phys. Rev. Lett. 96, 085501 (2006)]. With this formula, the composition dependence of the hardness is investigated for titanium nitrogencarbide (TiN1-xCx), off-stoichiometric transition-metal nitrides (TiN1-x and VN1-x), and B-doped semiconductors. The predicted hardness is in good agreement with experiments. To investigate the most frequently quoted correlation between hardness and elastic modulus, the elastic moduli of the systems involved in this paper have also been calculated. The results show that the elastic moduli cannot be used for rigorous predictions of the hardness of the solid solutions.

  • 229. Hu, Q. M.
    et al.
    Li, S. J.
    Hao, Y. L.
    Yang, R.
    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.
    Phase stability and elastic modulus of Ti alloys containing Nb, Zr, and/or Sn from first-principles calculations2008Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 93, nr 12Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The alloying effects of Nb, Zr, and/or Sn on the phase stability and elastic properties of Ti are investigated by using a first-principles method. Our calculation results indicate that a carefully designed Ti-Nb-Zr-Sn system can be a good candidate for low modulus biomedical materials. We find that the well-known correlation between the e/a ratio and both elastic and phase stabilities for Ti alloyed with transition metal elements breaks down for the Ti-Sn alloy.

  • 230.
    Hu, Qing-Miao
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Chun-Mei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kulkova, Svetlana E.
    Institute of Strength Physics and Materials Science, Siberian Branch of Russian Academy of Science, Russia.
    Yang, Rui
    Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, China.
    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.
    Magnetoelastic effects in Ni2Mn1+xGa1-x alloys from first-principles calculations2010Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, nr 6, s. 064108-1-064108-5Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The magnetic coupling between Mn atoms on Ga sublattice (Mn-Ga) and Mn atoms on Mn sublattice (Mn-Mn) in Ni2Mn1+xGa1-x alloy and its effect on the elastic modulus of the alloy are investigated by the use of first-principles methods. It is shown that, for x = 0.25, the state with antiparallel Mn-Ga-Mn-Mn magnetic coupling is slightly more stable than that with parallel coupling, whereas for x = 0.10, both magnetic states are almost degenerated. For both antiparallel and parallel Mn-Ga-Mn-Mn magnetic couplings, the bulk modulus (B) of Ni2Mn1+xGa1-x deviates from the general e/a-B relationship with e/a being the number of valence electrons per atom. The shear modulus C' versus the martensitic transformation temperature T-M for Ni2Mn1+xGa1-x with antiparallel Mn-Ga-Mn-Mn magnetic coupling is in line with the general C'-T-M relationship for Ni2MnGa-based alloys, in contrast to the case of parallel Mn-Ga-Mn-Mn magnetic coupling.

  • 231.
    Hu, Qing-Miao
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Chun-Mei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Yang, Rui
    Kulkova, Svetlana E.
    Institute of Strength Physics and Materials Science, Siberian Branch of Russian Academy of Science, Russia.
    Bazhanov, Dmitry I.
    Faculty of Physics, Moscow State University, Russia.
    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.
    Site occupancy, magnetic moments, and elastic constants of off-stoichiometric Ni2MnGa from first-principles calculations2009Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, nr 14Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The site occupancy and elastic modulus of off-stoichiometric Ni2MnGa alloys are investigated by the use of the first-principles exact muffin-tin orbital method in combination with coherent-potential approximation. The stable site occupancy at 300 K is determined by comparing the free energies of the alloys with different site-occupation configurations. It is shown that, for most of the off-stoichiometric Ni2MnGa, the "normal" site occupation is favorable, i.e., the excess atoms of the rich component occupy the sublattice(s) of the deficient one(s). Nevertheless, for the Ga-rich alloys, the excess Ga atoms have strong tendency to take the Mn sublattice no matter if Mn is deficient or not. Based on the determined site occupancy, the elastic moduli of the off-stoichiometric Ni2MnGa are calculated. We find that, in general, the bulk modulus increases with increasing e/a ratio (i.e., the number of valence electrons per atom). The shear moduli C-' and C-44 change oppositely with e/a ratio: C-' decreases but C-44 increases with increasing e/a. However, the Mn-rich Ga-deficient alloys deviate significantly from this general trend. The correlation of calculated elastic moduli and available experimental martensitic transformation temperatures (T-M) demonstrates that the alloy with larger C-' than that of the perfect Ni2MnGa generally possesses lower T-M except for Ni2Mn1+xGa1-x.

  • 232. Hu, Qing-Miao
    et al.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Yang, Rui
    Theoretical investigation of the omega-related phases in TiAl-Nb/Mo alloys2014Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, nr 5, s. 054109-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The incorporation of cubic beta/beta(0) phase improves significantly the ductility and workability of TiAl-based alloys. However, the ductility deteriorates with the precipitation of the ordered hexagonal omega(0) phase in the beta/beta(0) phase. To avoid the formation of the omega(0) phase in alloy design, fundamentals about the beta/beta(0) to omega(0) phase transition and its alloying element dependence have to be known. In the present work, we investigated the phase transition and phase stability in Ti4Al3Nb and Ti4Al3Mo alloys using a first-principles method based on density functional theory. Our calculations indicate that for the beta(0) to omega(0) transition, the "collapse-diffusion" pathway is easier than the "diffusion-collapse" one; however, both pathways are quite difficult due to the high-energy barriers. The beta(0) to omega '' transition occurs through the "diffusion-collapse" pathway without an energy barrier (except for the activation energy for the short-range diffusion needed for atomic rearrangement). Comparing the total energies of different phases, we find that the omega(0) phase of Ti4Al3Nb is more stable than beta(0) and vice versa for Ti4Al3Mo whereas the relative stability of omega '' to beta(0) for Ti4Al3Nb is stronger than that for Ti4Al3Mo, indicating that the addition of Mo inhibits the transition from the beta(0)- to the omega-related phases in Ti4Al3Nb. Our calculations demonstrate that omega '' is more stable than omega(0) for both Ti4Al3Nb and Ti4Al3Mo, in contrast to the previously proposed picture based on some experimental observations, the possible origins of which are discussed in detail.

  • 233. Hu, Q.M.
    et al.
    Yang, R.
    Lu, J.M.
    Wang, L.
    Li, Y.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.
    Effect of Zr on the properties of (TiZr)Ni alloys from first-principles calculations2007Inngår i: Physical Review B, ISSN 0163-1829, Vol. 76, s. 224201-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effect of Zr on the martensitic transformation (MT) behavior and mechanical properties of (Ti(0.5-x)Zr(x))Ni(0.5) alloys is investigated by calculating the elastic constants and elastic moduli in the B2 phase as a function of x for 0 <= x <= 0.2. The calculations are performed using the coherent potential approximation implemented within the framework of the exact muffin-tin orbitals method. We find that the theoretical elastic properties correlate well with the behavior of the MT. With increasing Zr concentration, the anisotropy of the alloy decreases, indicating that the nonbasal plane shear on which the modulus C(44) plays an important role, dominates and, therefore, a monoclinic martensitic phase should result. The experimental Zr content dependence of the MT temperature is paralleled with the calculated C(44) versus Zr content. The theoretical elastic moduli demonstrate that the (TiZr)Ni alloys, with Zr distributed randomly on the Ti sublattice, are intrinsically ductile, which suggests that the poor ductility of these alloys may be ascribed to some other factors, for example, impurities, precipitation, and grain boundaries.

  • 234.
    Huang, Dan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Band gap change induced by defect complexes in Cu2ZnSnS42013Inngår i: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 535, s. 265-269Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Understanding the impact on the electronic and optical properties of kesterite Cu2ZnSn(S,Se)(4) due to the presence of native defects is crucial for designing and manufacturing efficient solar cells. In this work, we complement earlier published theoretical studies by investigating the change in the Cu2ZnSnS4 band gap energy induced by the dominating isovalent (Zn (Cu) + Cu-Zn) and (Zn-Cu + V-Cu) defect complexes and the corresponding larger [(Zn-Cu + Cu-Zn)+(Zn-Cu + V-Cu)] complex. The study is based on the generalized gradient approximation with corrections for on-site Coulomb interactions (GGA + U) and the Heyd-Scuseria-Ernzerh hybrid functional method (HSE06) within the first-principles density functional theory. We find that (Zn-Cu + Cu-Zn) and (Zn-Cu + V-Cu) affect the band gap energies in an opposite way: (Zn-Cu + Cu-Zn) decreases the gap whereas (Zn-Cu + V-Cu) increases the gap. However, there is a strong correlation between these two defect complexes. The presence of the Cu-poor (Zn-Cu + V-Cu) defect complex lowers the formation energy of the antisite (Zn-Cu + Cu-Zn) defect complex in close configuration, and vice versa. Thereby, and considering the opposite effect on the band gap for (Zn-Cu + Cu-Zn) and (Zn-Cu + V-Cu), our results indicate that the band gap energy will be compensated and stabilized in Cu-poor Cu2ZnSnS4. We discuss the underlying mechanisms behind the band gap physics of the considered isovalent defect complexes.

  • 235.
    Huang, Dan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Stability of the bandgap in Cu-poor CuInSe22012Inngår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 24, nr 45, s. 455503-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Recent photoluminescence studies report that the bandgap energy E-g approximate to 1.0 eV of CuInSe2 is stable for Cu-poor compounds [Cu]/[In] < 1, despite the fact that Cu vacancies and (In-Cu + 2V(Cu)) complexes increase the energy gap. In this work, the impact on E-g due to the presence of native defects is analyzed using a screened hybrid density functional approach. We demonstrate that the formation energy of neutral (Cu-In + In-Cu) anti-site dimers decreases for CuInSe2 compounds when [Cu]/[In] decreases. This is explained in terms of the octet rule for the Se atoms next to the (In-Cu + 2V(Cu)) defects. As a consequence, Cu-poor CuInSe2 involves the large [(In-Cu + 2V(Cu)) + (Cu-In + In-Cu)] complexes where the anti-site defects stabilize E-g, in agreement with experimental findings.

  • 236.
    Huang, He
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Sci & Technol Surface Phys & Chem Lab, Mianyang 621900, Peoples R China..
    Li, Xiaoqing
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Dong, Zhihua
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Huang, Shuo
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Meng, Daqiao
    Sci & Technol Surface Phys & Chem Lab, Mianyang 621900, Peoples R China..
    Lai, Xinchun
    Sci & Technol Surface Phys & Chem Lab, Mianyang 621900, Peoples R China..
    Liu, Tianwei
    Sci & Technol Surface Phys & Chem Lab, Mianyang 621900, Peoples R China..
    Zhu, Shengfa
    Sci & Technol Surface Phys & Chem Lab, Mianyang 621900, Peoples R China..
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Dept Phys & Astron, Div Mat Theory, SE-75120 Uppsala, Sweden.;Wigner Res Ctr Phys, Inst Solid State Phys & Opt, H-1525 Budapest, Hungary..
    Critical stress for twinning nucleation in CrCoNi-based medium and high entropy alloys2018Inngår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 149, s. 388-396Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The CrCoNi-based medium and high entropy alloys (MHEAs) have drawn much attention due to their exceptional mechanical properties at cryogenic temperatures. The twinning critical resolved shear stress (CRSS) is a fundamental parameter for evaluating the strength-ductility properties of MHEAs. Here we construct and apply an extended twinning nucleation Peierls-Nabarro (P-N) model to predict the twinning CRSSes of face-centered cubic (FCC) CrCoNi-based MHEAs. The order of the twinning CRSSes of the selected alloys is CrCoNi > CrCoNiMn > CrCoNiFe > CrCoNiFeMn and the values are 291, 277, 274 and 236 MPa, respectively. These theoretical predictions agree very well with the experimental twinning CRSSes of CrCoNi and CrCoNiFeMn accounting for 260 +/- 30 and 235 +/- 10 MPa, respectively and are perfectly consistent with the strength-ductility properties including yield stress, ultimate tensile stress and uniform elongation for fracture of the FCC CrCoNi-based MHEAs obtained at cryogenic temperatures. The present method offers a first-principle quantum-mechanical tool for optimizing and designing new MHEAs with exceptional mechanical properties. 

  • 237. Huang, L. M.
    et al.
    Araujo, Carlos Moyses
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Magnetic and electronic properties of 3d transition-metal-doped In2O3: An ab initio study2009Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 87, nr 2Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The magnetic and electronic properties of the transition metal (TM) (V, Cr, Mn, Fe, Co, Ni, Cu) doped In2O3 have been theoretically studied by using the density functional theory. When two TM ions are placed close to each other (TM-TM distance of about 3.4 angstrom), the ferromagnetic ordering is found to be the lowest-energy configuration. The only exception is Fe, which possesses a half-filled 3d band. However, for further separation distance of about 7.2 angstrom, only Co, Ni and Cu ions (having more than half-filled 3d band) still prefer the ferromagnetic orientation, while V, Cr, or Mn ions (having less than half-filled 3d band) prefer antiferromagnetic ordering. The energies of the 3d band for TM ions show a decrease with increasing TM atomic number. For V, Cr and Mn, the 3d bands are merged with the conduction band, and show less hybridization with the host valence band; while for Co, Ni and Cu, the 3d bands show strong hybridization with the host valence band mainly formed by the oxygen 2p state. In this situation, polarized holes are formed on the oxygen sites close to the TM ions. Moreover, V-doped In2O3 is found to meet the requirements for a strong donor-mediated ferromagnetism.

  • 238. Huang, L. M.
    et al.
    Silvearv, F.
    Araujo, Carlos Moyses
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Defect-induced strong ferromagnetism in Cr-doped In2O3 from first-principles theory2010Inngår i: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 150, nr 13-14, s. 663-665Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We demonstrate by means of first-principles calculations that the high Curie temperature observed in Cr-doped In2O3 is mediated by intrinsic p-type defects, namely In vacancies or O interstitials. Charge transfer from Cr 3d states to the hole states formed by these defects makes Cr ions in the mixed valence state, giving rise to a strong ferromagnetic coupling. Calculated formation energies of various defects also show that doping Cr in In2O3 could greatly lower the formation energies of p-type intrinsic defects even in oxygen-deficient growth conditions. These results advance our understanding of the underlying physics of diluted magnetic oxides.

  • 239. Huang, L. M.
    et al.
    Århammar, Cecilia
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Araujo, José
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Silvearv, F.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Tuning magnetic properties of In2O3 by control of intrinsic defects2010Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 89, nr 4Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The electronic structure and magnetic properties of In2O3 with four kinds of intrinsic point defects (O vacancy, In interstitial, O interstitial, and In vacancy) have been theoretically studied using the density functional theory. The defect energy states of the O vacancy and In interstitial are close to the bottom of conduction band and act as shallow donors, while the defect energy states of the In vacancy and O interstitial are just above the top of the valence band and act as shallow acceptors. Without addition of any magnetic ions, all the hole states are completely spin polarized, while the electron states display no spin polarization. This implies that semiconducting In2O3 can display magnetic ordering, purely due to the intrinsic defects. However, the formation energies for neutral p-type defects are too high to be thermodynamically stable at reasonable temperatures. Nevertheless, it is shown that negative charging can greatly decrease the formation energies of p-type defects, simultaneously removing the local magnetic moments. We conlcude that V-In''' and O-I '' will be the dominant compensating defects as In2O3 is doped with TM ions, such as Sn, Mo, V and Cr. This result is consistent with the general view that the p-type defect is a key feature to mediate ferromagnetic coupling between transition metal ions of dilute concentration in metal oxides.

  • 240. Huang, L.
    et al.
    Ramzan, M.
    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.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Anomalous temperature dependence of elastic constant c(44) in V, Nb, Ta, Pd, and Pt2010Inngår i: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 71, nr 8, s. 1065-1068Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    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.

  • 241. Huang, L.
    et al.
    Skorodumova, N. V.
    Belonoshko, Anatoly B.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Carbon in iron phases under high pressure2005Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 32, nr 21Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The influence of carbon impurities on the properties of iron phases (bcc, hcp, dhcp, fcc) has been studied using the first-principles projector augmented-wave ( PAW) method for a wide pressure range. It is shown that the presence of similar to 6 at. % of interstitial carbon has a little effect on the calculated structural sequence of the iron phases under high pressure. The bcc ! hcp transition both for pure iron and iron containing carbon takes place around 9 GPa. According to the enthalpies comparison, the solubility of carbon into the iron solid is decreased by high pressure. The coexistence of iron carbide (Fe3C) + pure hcp Fe is most stable phase at high pressure compared with other phases. Based on the analysis of the pressure-density dependences for Fe3C and hcp Fe, we suggest that there might be some fraction of iron carbide present in the core.

  • 242. Huang, L.
    et al.
    Vitos, Levente
    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.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Thermoelastic properties of random alloys from first-principles theory2006Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 73, nr 10Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a first-principles description of the temperature-dependent elastic constants in random alloys. The substitutional disorder is treated using the coherent potential approximation implemented within the frameworks of exact muffin-tin orbitals theory. The temperature effects are approximated as the sum of electronic and thermal expansion contributions. Calculations on pure Nb demonstrate that this approach correctly accounts for the main temperature dependence of cubic elastic constants. When extended to Nb-Zr solid solution, the theoretical results show good agreement with experiments at temperatures less than or similar to 300 K.

  • 243.
    Huang, Shou
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vida, Á.
    Molnár, D.
    Kádas, K.
    Varga, L. K.
    Holmström, E.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Box 516, Uppsala, Sweden.
    Phase stability and magnetic behavior of FeCrCoNiGe high-entropy alloy2015Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 107, nr 25Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report an alternative FeCrCoNiGe magnetic material based on FeCrCoNi high-entropy alloy with Curie point far below the room temperature. Investigations are done using first-principles calculations and key experimental measurements. Results show that the equimolar FeCrCoNiGe system is decomposed into a mixture of face-centered cubic and body-centered cubic solid solution phases. The increased stability of the ferromagnetic order in the as-cast FeCrCoNiGe composite, with measured Curie temperature of 640 K, is explained using the exchange interactions.

  • 244.
    Huang, Shuo
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Quantum-Mechanical Modeling of High-Entropy Alloys2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    High-entropy alloys (HEAs) consisting of multi-principal elements open up a near-infinite compositional space for materials design. Extensive attention has been put on HEAs, and interesting structural, physical and chemical properties are being continuously revealed. Based on first-principle theory, here we focus on the fundamental characteristics of HEAs, as well as on the optimization and prediction of alternative alloy with promising technological applications.

    The relative phase stability of different-types of HEAs is investigated from the minimum of structural energy, and the composition-, temperature-, and ordering-induced phase transformations are presented. The elastic properties are discussed through the single-crystal and polycrystalline elastic moduli by making use of a series of phenomenological models. The competition between full slip, twinning, and stacking fault in face-centered cubic HEAs is analyzed by studying the generalized stacking fault energy. The magnetic characteristics are provided through the Heisenberg Hamiltonian model in connection with Monte-Carlo simulation, and the Curie temperature of a large number of cubic HEAs is mapped out with the help of mean-filed approximation. The thermal expansion behavior is estimated by using the Debye-Grüneisen model.

    This work provides some fundamental and pioneering theoretical points of view to understand the intrinsic physical mechanisms in HEAs, and reveals alternative opportunities for optimizing and designing properties of materials. The challenge of comprehending the observed complex behavior behind the multi-component nature of HEAs is great, on the other hand, the potential to enhance the underlying theoretical understanding is remarkable.

  • 245.
    Huang, Shuo
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Theoretical Investigations of High-Entropy Alloys2017Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    High-entropy alloys (HEAs) are composed of multi-principal elements with equal or near-equal concentrations, which open up a vast compositional space for alloy design. Based on first-principle theory, we focus on the fundamental characteristics of the reported HEAs, as well as on the optimization and prediction of alternative HEAs with promising technological applications.

    The ab initio calculations presented in the thesis confirm and predict the relatively structural stability of different HEAs, and discuss the composition and temperature-induced phase transformations. The elastic behavior of several HEAs are evaluated through the single-crystal and polycrystalline elastic moduli by making use of a series of phenomenological models. The competition between dislocation full slip, twinning, and martensitic transformation during plastic deformation of HEAs with face-centered cubic phase are analyzed by studying the generalized stacking fault energy. The magnetic moments and magnetic exchange interactions for selected HEAs are calculated, and then applied in the Heisenberg Hamiltonian model in connection with Monte-Carlo simulations to get further insight into the magnetic characteristics including Curie point. The Debye-Grüneisen model is used to estimate the temperature variation of the thermal expansion coefficient.

    This work provides specific theoretical points of view to try to understand the intrinsic physical mechanisms behind the observed complex behavior in multi-component systems, and reveals some opportunities for designing and optimizing the properties of materials

  • 246.
    Huang, Shuo
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Holmstrom, Erik
    Sandvik Coromant R&D, S-12680 Stockholm, Sweden..
    Eriksson, Olle
    Uppsala Univ, Div Mat Theory, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden.;Orebro Univ, Sch Sci & Technol, SE-70182 Orebro, Sweden..
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala Univ; Wigner Res Ctr Phys.
    Mapping the magnetic transition temperatures for medium- and high-entropy alloys2018Inngår i: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 95, s. 80-84Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Tailorable magnetic state near room temperature is very promising for several technological, including magnetocaloric applications. Here using first-principle alloy theory, we determine the Curie temperature (T-C) of a number of equiatomic medium- and high-entropy alloys with solid solution phases. All calculations are performed at the computed lattice parameters, which are in line with the available experimental data. Theory predicts a large crystal structure dependence of T-C, which explains the experimental observations under specified conditions. The sensitivity of the magnetic state to the crystal lattice is reflected by the magnetic exchange interactions entering the Heisenberg Hamiltonian. The analysis of the effect of composition on T-C allows researchers to explore chemistry-dependent trends and design new multi-component alloys with pre-assigned magnetic properties.

  • 247.
    Huang, Shuo
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Huang, He
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Science and Technology on Surface Physics and Chemistry Laboratory, Mianyang, 621900, PR China.
    Li, Wei
    Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, SE-75120, Uppsala, Sweden.
    Kim, Dongyoo
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Department of Physics, Pukyung National University, Busan, 608-737, Republic of Korea.
    Lu, Song
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Xiaoqing
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Holmström, E.
    Kwon, S. K.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Twinning in metastable high-entropy alloys2018Inngår i: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 9, nr 1, artikkel-id 2381Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Twinning is a fundamental mechanism behind the simultaneous increase of strength and ductility in medium- and high-entropy alloys, but its operation is not yet well understood, which limits their exploitation. Since many high-entropy alloys showing outstanding mechanical properties are actually thermodynamically unstable at ambient and cryogenic conditions, the observed twinning challenges the existing phenomenological and theoretical plasticity models. Here, we adopt a transparent approach based on effective energy barriers in combination with first-principle calculations to shed light on the origin of twinning in high-entropy alloys. We demonstrate that twinning can be the primary deformation mode in metastable face-centered cubic alloys with a fraction that surpasses the previously established upper limit. The present advance in plasticity of metals opens opportunities for tailoring the mechanical response in engineering materials by optimizing metastable twinning in high-entropy alloys. 

  • 248.
    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.
    Holmström, Erik
    Sandvik Coromant R&D, S-12680 Stockholm, Sweden..
    Vitos, Levente
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Uppsala Univ, Dept Phys & Astron, Div Mat Theory, SE-75120 Uppsala, Sweden.;Inst Solid State Phys & Opt, Wigner Res Ctr Phys, H-1525 Budapest, Hungary..
    Phase-transition assisted mechanical behavior of TiZrHfTax high-entropy alloys2018Inngår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, artikkel-id 12576Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Recent developments of high-entropy alloys with high strength and high ductility draw attention to the metastability-engineering strategy. Using first-principle theory, here we demonstrate that reducing the Ta level in the refractory TiZrHfTax system destabilizes the body-centered cubic (bcc) phase and leads to the appearance of the hexagonal close-packed (hcp) phase embedded in the bcc matrix. The alloying-induced features of the elastic parameters for the cubic and hexagonal structures are mapped out in details, and strong sensitivity to the crystal lattice and chemistry is revealed. Results show softening of the bcc matrix with decreasing Ta concentration which ensures ductile behavior. However, the elastically nearly isotropic hcp precipitates possess enhanced resistance against shear which promotes strengthening of the TiZrHfTax dual-phase system. The present atomic-level insight provides strong evidence to the experimental observation, and emphasizes the significance of quantum-design for advanced multi-phase high-entropy alloys with excellent strength-ductility combinations.

  • 249.
    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.
    Holmström, Erik
    Sandvik Coromant R&D, S-12680 Stockholm, Sweden..
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Wigner Res Ctr Phys, Inst Solid State Phys & Opt, H-1525 Budapest, Hungary.;Uppsala Univ, Div Mat Theory, Dept Phys & Astron, SE-75120 Uppsala, Sweden..
    Strengthening Induced by MagnetoChemical Transition in Al-Doped Fe-Cr-Co-Ni High-Entropy Alloys2018Inngår i: Physical Review Applied, E-ISSN 2331-7019, Vol. 10, nr 6, artikkel-id 064033Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Alloys with adjustable mechanical performance are of fundamental interest in material designs. Here, we investigate the magnetic- and chemical-ordering behavior of the ferromagnetic Fe-Cr-Co-Ni-Al-x (1 <= x <= 2.5) high-entropy alloys with the help of first-principle alloy theory. The lattice constants and the single- and polycrystalline elastic parameters for partially ordered and random structures are considered. In contrast to the trend found for the completely disordered phase, we demonstrate that ordering driven primarily by Al results in an enhanced Young's modulus, especially at high-Al concentrations, which is in line with the observed increase of the hardness for systems with a body-centered-cubic underlying lattice. The results suggest that outstanding strength and ductility can be realized by proper control of the ordering level in single- and multiphase high-entropy alloys.

  • 250.
    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 alloys2016Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 103, s. 71-74Artikkel i tidsskrift (Fagfellevurdert)
    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.

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