Endre søk
Begrens søket
45678910 301 - 350 of 922
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Treff pr side
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
Merk
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 301.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Thorium: The first 5f element in the actinide series2013Inngår i: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 245, s. 119-NUCL-Artikkel i tidsskrift (Annet vitenskapelig)
  • 302.
    Johansson, Börje
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Sa
    Itinerant f-electron elements2009Inngår i: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 89, nr 22-24, s. 1793-1799Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    To obtain a proper understanding of the 5f elements, the actinides, it is useful to compare their behavior with the 4f transition elements, the lanthanides. It is especially rewarding to capitalize on the remarkable similarity between the solid-state properties of compressed Ce and the actinide metals. The intensively studied alpha-gamma transition in Ce is considered to be a Mott transition, namely, the 4f electron changes its behavior from being localized to become delocalized (itinerant/metallic). This change also means that the 4f electron transforms from a non-bonding to a bonding configuration which, in turn, gives rise to a volume collapse. This collapse is isostructural in character, which contributes to the immense interest in this phase transition. An analogous and remarkable change in bonding (cohesive) properties is also found within the actinide series, where the sudden volume increase from Pu to Am (50%) can be viewed as a Mott transition within the 5f shell as a function of atomic number Z. The elements on the metallic side of the 5f Mott transition, i.e. the earlier actinides (Pa-Pu), show low symmetry structures at ambient conditions, while the heavier elements (from Am and beyond) adopt structures typical for the lighter trivalent lanthanide elements with localized 4f electrons. An important consequence of the localized and trivalent behavior in Am is a non-magnetic 5f(6) (J = L + S = 0) configuration for the f electrons. This led to the prediction of superconductivity in americium and subsequently to its experimental verification.

  • 303.
    Johansson, Börje
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Sa
    The actinides - a beautiful ending of the Periodic Table2007Inngår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 444, s. 202-206Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The 5f elements, actinides, show many properties which have direct correspondence to the 4f transition metals, the lanthanides. The remarkable similarity between the solid state properties of compressed Ce and the actinide metals is pointed out in the present paper. The alpha-gamma transition in Ce is considered as a Mott transition, namely, from delocalized to localized 4f states. An analogous behavior is also found for the actinide series, where the sudden volume increase from Pu to Am can be viewed upon as a Mott transition within the 5f shell as a function of the atomic number Z. On the itinerant side of the Mott transition, the earlier actinides (Pa-Pu) show low symmetry structures at ambient conditions; while across the border, the heavier elements (Am-Cf) present the dhcp structure, an atomic arrangement typical for the trivalent lanthanide elements with localized 4f magnetic moments. The reason for an isostructural Mott transition of the f electron in Ce, as opposed to the much more complicated cases in the actinides, is identified. The strange appearance of the delta-phase (fcc) in the phase diagram of Pu is another consequence of the border line behavior of the 5f electrons. The path leading from delta-Pu to alpha-Pu is identified.

  • 304.
    Johansson, Börje
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Luo, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden.
    Li, Sa
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University.
    Cerium; Crystal Structure and Position in The Periodic Table2014Inngår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 4, s. 6398-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The properties of the cerium metal have intrigued physicists and chemists for many decades. In particular a lot of attention has been directed towards its high pressure behavior, where an isostructural volume collapse (gamma phase -> alpha phase) has been observed. Two main models of the electronic aspect of this transformation have been proposed; one where the 4f electron undergoes a change from being localized into an itinerant metallic state, and one where the focus is on the interaction between the 4f electron and the conduction electrons, often referred to as the Kondo volume collapse model. However, over the years it has been repeatedly questioned whether the cerium collapse really is isostructural. Most recently, detailed experiments have been able to remove this worrisome uncertainty. Therefore the isostructural aspect of the a-c transition has now to be seriously addressed in the theoretical modeling, something which has been very much neglected. A study of this fundamental characteristic of the cerium volume collapse is made in present paper and we show that the localized reversible arrow delocalized 4f electron picture provides an adequate description of this unique behavior. This agreement makes it possible to suggest that an appropriate crossroad position for cerium in The Periodic Table.

  • 305.
    Johansson, Börje
    et al.
    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.
    Abrikosov, I. A.
    Comment on "thermal signatures of the Kondo volume collapse in cerium"2009Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 102, nr 18, s. 189601-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A Comment on the Letter by M.J. Lipp et al., Phys. Rev. Lett.PRLTAO0031-9007 101, 165703 (2008)10.1103/PhysRevLett.101.165703

  • 306.
    Johansson, Börje Örje
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Sa
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Isaev, E.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Theoretical study of protactinium at high pressure2006Inngår i: Mater Res Soc Symp Proc, 2006, s. 255-269Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We have studied the crystal structure of Pa metal under high pressure by means of first-principles calculations based on the density functional theory (DFT) using the generalized gradient approximation (GGA). The body centered tetragonal (bct) to orthorhombic (α-U) phase transition was calculated to take place at 29 GPa and with a volume change of 1.3%. The calculated c/a for the bet phase reaches the ideal c/a value (0.816) at around 50 GPa. A bulk modulus of 113 GPa was derived from a Murnaghan equation of state (EOS) fitting procedure. Our results are in general good agreement with recent experiment performed by Haire et al, [Phys. Rev. B 67, 134101 (2003)]. We have also calculated phonon spectra for fcc, bct and bcc Pa. The bcc spectrum gives imaginary frequencies showing the low temperature instability of this crystallographic phase for Pa.

  • 307. Johansson, Malin B.
    et al.
    Baldissera, Gustavo
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Valyukh, Iryna
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. University of Oslo, Norway.
    Arwin, Hans
    Niklasson, Gunnar A.
    Österlund, Lars
    Electronic and optical properties of nanocrystalline WO3 thin films studied by optical spectroscopy and density functional calculations2013Inngår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 25, nr 20, s. 205502-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The optical and electronic properties of nanocrystalline WO3 thin films prepared by reactive dc magnetron sputtering at different total pressures (P-tot) were studied by optical spectroscopy and density functional theory (DFT) calculations. Monoclinic films prepared at low P-tot show absorption in the near infrared due to polarons, which is attributed to a strained film structure. Analysis of the optical data yields band-gap energies E-g approximate to 3.1 eV, which increase with increasing P-tot by 0.1 eV, and correlate with the structural modifications of the films. The electronic structures of triclinic delta-WO3, and monoclinic gamma- and epsilon-WO3 were calculated using the Green function with screened Coulomb interaction (GW approach), and the local density approximation. The delta-WO3 and gamma-WO3 phases are found to have very similar electronic properties, with weak dispersion of the valence and conduction bands, consistent with a direct band-gap. Analysis of the joint density of states shows that the optical absorption around the band edge is composed of contributions from forbidden transitions (>3 eV) and allowed transitions (>3.8 eV). The calculations show that E-g in epsilon-WO3 is higher than in the delta-WO3 and gamma-WO3 phases, which provides an explanation for the P-tot dependence of the optical data.

  • 308.
    Johansson, Malin B.
    et al.
    Uppsala Univ, Dept Chem, Div Phys Chem, Angstrom Lab, Box 523, SE-75120 Uppsala, Sweden..
    Philippe, Bertrand
    Uppsala Univ, Dept Phys & Astron, Div Mol & Condensed Matter Phys, SE-75120 Uppsala, Sweden..
    Banerjee, Amitava
    Uppsala Univ, Dept Phys & Astron, Mat Theory Div, Condensed Matter Theory Grp, Box 516, SE-75120 Uppsala, Sweden..
    Phuyal, Dibya
    Uppsala Univ, Dept Phys & Astron, Div Mol & Condensed Matter Phys, SE-75120 Uppsala, Sweden..
    Mukherjee, Soham
    Uppsala Univ, Dept Phys & Astron, Div Mol & Condensed Matter Phys, SE-75120 Uppsala, Sweden..
    Chakraborty, Sudip
    Uppsala Univ, Dept Phys & Astron, Mat Theory Div, Condensed Matter Theory Grp, Box 516, SE-75120 Uppsala, Sweden..
    Cameau, Mathis
    Uppsala Univ, Dept Phys & Astron, Div Mol & Condensed Matter Phys, SE-75120 Uppsala, Sweden..
    Zhu, Huimin
    Uppsala Univ, Dept Chem, Div Phys Chem, Angstrom Lab, Box 523, SE-75120 Uppsala, Sweden..
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala Univ, Dept Phys & Astron, Mat Theory Div, Condensed Matter Theory Grp, Box 516, SE-75120 Uppsala, Sweden..
    Boschloo, Gerrit
    Uppsala Univ, Dept Chem, Div Phys Chem, Angstrom Lab, Box 523, SE-75120 Uppsala, Sweden..
    Rensmo, Hakan
    Uppsala Univ, Dept Phys & Astron, Div Mol & Condensed Matter Phys, SE-75120 Uppsala, Sweden..
    Johansson, Erik M. J.
    Uppsala Univ, Dept Chem, Div Phys Chem, Angstrom Lab, Box 523, SE-75120 Uppsala, Sweden..
    Cesium Bismuth Iodide Solar Cells from Systematic Molar Ratio Variation of CsI and BiI32019Inngår i: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 58, nr 18, s. 12040-12052Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Metal halide compounds with photovoltaic properties prepared from solution have received increased attention for utilization in solar cells. In this work, low-toxicity cesium bismuth iodides are synthesized from solution, and their photovoltaic and, optical properties as well as electronic and crystal structures are investigated. The X-ray diffraction patterns reveal that a CsI/BiI3 precursor ratio of 1.5:1 can convert pure rhombohedral BiI3 to pure hexagonal Cs3Bi2I9, but any ratio intermediate of this stoichiometry and pure BiI3 yields a mixture containing the two crystalline phases Cs3Bi2I9 and BiI3, with their relative fraction depending on the CsI/BiI3 ratio. Solar cells from the series of compounds are characterized, showing the highest efficiency for the compounds with a mixture of the two structures. The energies of the valence band edge were estimated using hard and soft X-ray photoelectron spectroscopy for more bulk and surface electronic properties, respectively. On the basis of these measurements, together with UV-vis-near-IR spectrophotometry, measuring the band gap, and Kelvin probe measurements for estimating the work function, an approximate energy diagram has been compiled clarifying the relationship between the positions of the valence and conduction band edges and the Fermi level.

  • 309. Joyce, J. J.
    et al.
    Wills, J. M.
    Durakiewicz, T.
    Butterfield, M. T.
    Guziewicz, E.
    Moore, D. P.
    Sarrao, J. L.
    Morales, L. A.
    Arko, A. J.
    Eriksson, O.
    Delin, Anna
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Graham, K. S.
    Dual nature of the 5f electrons in plutonium materials2006Inngår i: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 378-80, s. 920-924Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The electronic structure of select Pu materials is examined by means of photoemission (PES) and model calculations. We present the first photoemission results and electronic structure calculations for the material PuIn3. Results for Pu materials, including the cubic delta-phase metal and the superconductor PuCoGa5, give indication of the 5f electrons exhibiting both localized and itinerant character. These new results for PuIn3 place this compounds also in the 5f dual nature category. The dual nature of the Pu 5f electrons demarks the boundary between localized and itinerant 5f character in the actinides. The photoemission data for delta-Pu, PuIn3 and PuCoGa5 are compared against model calculations. The calculations are a mixed level model (MLM) which is a multi-electron extension of the generalized gradient approximation. Using the MLM, one obtains good agreement for the volume and total energy minimum with 4 of 5 Pu 5f electrons localized. The calculations also agree well with the PES spectra. Other computational schemes and interpretations are also reviewed.

  • 310. Kabliman, Evgeniya
    et al.
    Blaha, Peter
    Schwarz, Karlheinz
    Peil, Oleg E.
    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.
    Configurational thermodynamics of the Fe-Cr sigma phase2011Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, nr 18, s. 184206-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Configurational thermodynamics of the Fe-Cr sigma phase is investigated on the basis of an Ising-type configurational Hamiltonian and a single-site mean-field model for the free energy. The parameters of the statistical models are obtained from efficient first-principles calculations using different computational techniques. We demonstrate that the effective pair and multisite interactions in the sigma phase are relatively small, which allows using a simplified model for distributing Fe and Cr atoms among sublattices. We also show that this system exhibits a nontrivial magnetic behavior at high temperatures, which affects the site occupation by Fe and Cr atoms. The structural variation (volume and c/a) that might be present due to neutron irradiation and thermal expansion can lead to an additional atomic redistribution.

  • 311. Kabliman, Evgeniya
    et al.
    Blaha, Peter
    Schwarz, Karlheinz
    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.
    Ab initio-based mean-field theory of the site occupation in the Fe-Cr sigma-phase2011Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 83, nr 9, s. 092201-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An efficient first-principles-based mean-field theory is applied to study the site occupations in the Fe-Cr sigma phase. It is based on the expansion of the total energy of a random alloy close to the equiatomic composition in the paramagnetic state in terms of the effective on-site interactions and takes into account longitudinal spin fluctuations at high temperatures. The calculated site occupation is in very good agreement with the existing experimental data.

  • 312. Kabliman, Evgeniya
    et al.
    Ruban, Andrei V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Blaha, Peter
    Peil, Oleg
    Schwarz, Karlheinz
    Ab Initio Study of Lattice Site Occupancies in Binary Sigma Phases Using a Single-Site Mean Field Model2012Inngår i: Applied Sciences, E-ISSN 2076-3417, Vol. 2, nr 3, s. 654-668Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The site occupation of binary Fe-Cr, Co-Cr, Re-W and Fe-V sigma phases is studied in the present work with a first-principles-based single-site mean field theory. We show that the alloy components in these systems exhibit similar site preferences except for the Re-W system, where the occupation of two sites is reversed in agreement with previously published works. In case of the FeV sigma phase, for which the size mismatch between the alloy components is large, we also include into our consideration the effect of local lattice relaxations. The obtained results are found in good agreement with the experimental data and previous theoretical studies.

  • 313. Kadas, K.
    et al.
    Lindquist, M.
    Eriksson, O.
    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.
    Magnetism-driven anomalous surface alloying between Cu and Cr2009Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 94, nr 17Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cu-Cr contact materials are widely used as medium- and high-voltage vacuum interrupters. The microstructure of these materials is critical in their performance: the finer structure they have, the better are their physical properties. A solid solution of Cu and Cr could significantly increase the performance of such contact materials. However, Cu and Cr are practically immiscible in the bulk phase. Based on first principles density functional theory we show here that the solubility of Cr in Cu is dramatically increased on Cu surfaces already at room temperature and Cu-Cr alloys are formed on both the Cu(111) and Cu(100) surfaces. We demonstrate that the origin of this phenomenon is the unique magnetic properties of Cr atoms near surfaces.

  • 314. Kadas, K.
    et al.
    Nabi, Z.
    Kwon, S. K.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kollar, J.
    Surface relaxation and surface stress of 4d transition metals2006Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 600, nr 2, s. 395-402Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Using the density functional theory formulated within the framework of the exact muffin-tin orbitals method, we present a systematic study of the top layer relaxation and surface stress of 4d transition metals. Our calculations predict layer contractions for most surfaces. We also find that the relaxations of the close packed surfaces decrease with increasing atomic number through the 4d series. We propose that the relaxation is mainly due to the reduction of the number of sp electrons in the surface layer relative to bulk. The surface stress is found to be very sensitive to the relaxation and, therefore, an accurate determination of the layer relaxation is necessary for obtaining reliable values for the surface stress. Comparing the top layer relaxations for the close packed surfaces, we see essential deviations between data derived in different ab initio calculations. At the same time, the overall trend for the present surface stress of 4d metals is in reasonable agreement with recent full-potential data.

  • 315. Kadas, K.
    et al.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Elastic properties of iron-rich hcp Fe-Mg alloys up to Earth's core pressures2008Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 271, nr 1-4, s. 221-225Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Using density functional theory formulated within the framework of the exact muffin-tin orbital method, we investigate the elastic properties of hexagonal closed-packed Fe-Mg alloys, containing 5 and 10 at.% Mg, up to pressures of the Earth's inner core. We demonstrate the effect of Mg alloying on the hexagonal axial ratio, elastic constants, density and sound wave velocities. We find that 10% Mg alloying decreases the shear modulus of iron by 23% and reduces the transverse sound velocity, nu(s) by 12% at core pressures. Although it is debated whether or not Mg can partition into the core, our results support Mg as a candidate light element in the core.

  • 316. Kadas, K.
    et al.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kollar, J.
    Temperature-dependent elastic properties of alpha-beryllium from first principles2007Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 76, nr 23Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Using density functional theory formulated within the framework of the exact muffin-tin orbitals method, we investigate the temperature dependence of the structural parameters and the elastic properties of the hexagonal closed-packed phase of Be (alpha-Be). We find that the elastic constants follow a normal behavior with temperature: decrease with increasing temperature with a slightly increasing slope. Up to the melting point, the monocrystalline elastic constants decrease by an average of 16% and the polycrystalline elastic constants by 10%. These trends contradict the large temperature factor observed in high-temperature direct pulse ultrasonic experiments. At the same time, the low-temperature pulse echo measurements confirm the present theoretical findings. Our results call for further accurate experimental studies on the elastic properties of alpha-Be at high temperatures.

  • 317. Kadas, K.
    et al.
    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.
    Stability of body-centered cubic iron-magnesium alloys in the Earth's inner core2009Inngår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 106, nr 37, s. 15560-15562Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The composition and the structure of the Earth's solid inner core are still unknown. Iron is accepted to be the main component of the core. Lately, the body-centered cubic (bcc) phase of iron was suggested to be present in the inner core, although its stability at core conditions is still in discussion. The higher density of pure iron compared with that of the Earth's core indicates the presence of light element(s) in this region, which could be responsible for the stability of the bcc phase. However, so far, none of the proposed composition models were in full agreement with seismic observations. The solubility of magnesium in hexagonal Fe has been found to increase significantly with increasing pressure, suggesting that Mg can also be an important element in the core. Here, we report a first-principles density functional study of bcc Fe-Mg alloys at core pressures and temperatures. We show that at core conditions, 5-10 atomic percent Mg stabilizes the bcc Fe both dynamically and thermodynamically. Our calculated density, elastic moduli, and sound velocities of bcc Fe-Mg alloys are consistent with those obtained from seismology, indicating that the bcc-structured Fe-Mg alloy is a possible model for the Earth's inner core.

  • 318. Kadas, K.
    et al.
    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.
    Kollar, J.
    Structural stability of beta-beryllium2007Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, nr 3Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Using density-functional theory formulated within the framework of the exact muffin-tin orbitals method, we investigate the stability of the body-centered-cubic phase of Be (beta-Be). The elastic constants and Debye temperature of beta-Be are calculated over a wide volume range and compared to those obtained for the low-temperature hexagonal phase (alpha-Be). A significant difference in the anisotropy of the bcc and hcp structures is found. In line with experiments, we predict that the hcp -> bcc phase transition occurs at 240 GPa at 0 K and 239 GPa at ambient temperature. We find that the cubic shear constant C '=(C-11-C-12)/2 rapidly decreases for volumes above similar to 1.05V(0), where V-0 is the zero temperature equilibrium volume for beta-Be. At 1.17V(0), the stability condition C-'> 0 is violated and the bcc phase becomes mechanically unstable. We demonstrate that at 0 K, the softening of beta-Be near its experimental volume of 1.063V(0) is related to an electronic topological transition due to the increased number of occupied s states near the Fermi level compared to that at V-0. This softening turns out to be important for the stability of the bcc phase before melting. The disclosed electronic topological transition is found to be present in other analogous hexagonal metals as well.

  • 319. Kadas, Krisztina
    et al.
    da Costa, Marcio Teles
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Andersson, Yvonne
    Bergman, Anders
    Eriksson, Olle
    On the icosahedral metal-phosphorus coordination in melliniite: a gift from the sky for materials chemistry2012Inngår i: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 22, nr 29, s. 14741-14745Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Recently a new mineral, melliniite, was reported from a meteorite sample. This mineral has an ideal chemical composition of (Ni,Fe)(4)P and a crystal structure where the phosphorus atoms are coordinated by twelve nearest neighboring metal atoms. No other phosphide has been reported to have such high metal coordination. Therefore melliniite provides new and important information about the chemical interaction in transition metal chalcogenides and possibly pnictides. We demonstrate here, using first principles theory, that the stability and icosahedral metal-phosphorous coordination of melliniite are due to a balance between covalent Fe-P binding, configurational entropy and a weaker nickel-phosphorus binding, that has only a weak directional dependence.

  • 320. Kaewmaraya, T.
    et al.
    Kim, Duck Young
    Lebegue, S.
    Pickard, C. J.
    Needs, R. J.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Theoretical investigation of xenon-hydrogen solids under pressure using ab initio DFT and GW calculations2011Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, nr 9, s. 092101-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have calculated crystal structures and electronic properties of Xe-H(2) compounds under high pressures using first-principles density functional theory calculations and ab-initio random structure searching. We present results for the equation of state, Xe-Xe separations, and the electronic charge transfer between the Xe and H atoms. Our results are broadly consistent with experimental results by M. Somayazulu et al. [Nature Chem. 2, 50 (2010)]. We have in addition calculated the metallization pressure within the GW approximation, finding it to be around 250 GPa, which is close to the maximum pressure reached in the experiment.

  • 321. Kaewmaraya, T.
    et al.
    Pathak, B.
    Araujo, C. M.
    Rosa, A. L.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Water adsorption on ZnO(10(1)over-bar0): The role of intrinsic defects2012Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 97, nr 1, s. 17014-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Density functional theory (DFT) calculations have been performed to investigate the interaction of water molecules with bare and defective ZnO(10 (1) over bar0) surfaces. We show that at high coverages water molecules avoid adsorption close to defect sites, whereas at low coverages adsorption on defective surfaces show a similar adsorption pattern to those adsorbed on the defect-free surface, adsorbing in a molecular fashion. Finally we show that the electronic structure of the defective non-polar surface is not much affected by the adsorption of water, with exception of the O-defect surfaces.

  • 322. Kaewmaraya, T.
    et al.
    Ramzan, M.
    Löfås, H.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Hybrid density functional study of electronic and optical properties of phase change memory material: Ge2Sb2Te52013Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, nr 3, s. 033510-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this article, we use hybrid density functional (HSE06) to study the crystal and electronic structures and optical properties of well known phase change memory material Ge2Sb2Te5. We calculate the structural parameters, band gaps, and dielectric functions of three stable structures of this material. We also analyze the electron charge distribution using the Bader's theory of charge analysis. We find that hybrid density functional slightly overestimates the value of "c" parameter. However, overall, our results calculated with the use of hybrid density functional (HSE06) are very close to available experimental values than calculated with the use of Perdew Burke-Ernzerhof functional. Specifically, the electronic band gap values of this material calculated with HSE06 are in good agreement with the available experimental data in the literature. Furthermore, we perform the charge analysis and find that naive ionic model fails to explain the charge distribution between the constituent atoms, showing the complex nature of this compound.

  • 323. Kaewmaraya, T.
    et al.
    Ramzan, M.
    Osorio-Guillen, J. M.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Condensed Matter Theory Group, Department of Physics and Astronomy, Uppsala University.
    Electronic structure and ionic diffusion of green battery cathode material: Mg2Mo6S82014Inngår i: Solid State Ionics, ISSN 0167-2738, E-ISSN 1872-7689, Vol. 261, s. 17-20Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report ab-initio density functional theory calculations of crystal and electronic structure of Mg2Mo6S8, a candidate material to be used in rechargeable magnesium batteries, by employing hybrid exchange-correlation functionals. We find that Mg2Mo6S8 crystalizes in a triclinic geometry and it is a semiconductor with an indirect band gap. Ab-initio molecular dynamics shows that Mg ions present progressive diffusion starting at 200 K with a preferable path through the channel between Mo6S8 blocks along the [010] direction. The intercalation voltage of the system is also determined and the results show that the voltage evaluated by PBE and hybrid functionals likely implies the lower and the upper limit of the experimental value. Lastly, we confirm the dynamical stability of the crystal structure by the calculated phonon dispersion relation.

  • 324. Kaewmaraya, T.
    et al.
    Ramzan, M.
    Sun, WeiWei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Sagynbaeva, M.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Atomistic study of promising catalyst and electrode material for memory capacitors: Platinum oxides2013Inngår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 79, s. 804-810Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Platinum oxides have the technological importance as evidenced by numerous studies concentrating on their crystal structures to attain the clear atomistic understanding but the controversy exists between the experimental and theoretical studies. In our present study, we report the electronic and optical properties of crystalline PtO and PtO2 on the basis of Heyd-Scuseria-Ernzerhof (HSE06) functional within the framework of the density functional theory (DFT). We present the structural parameters, electronic and optical properties of several proposed structures of PtO and PtO2. We find that PtS-type structure of PtO and CaCl2-type structure of PtO2 are the most stable structures of these materials on the basis of hybrid functional and they appear to be semiconductors with band gap values of 0.87 eV and 1.85 eV, respectively. The mechanical stability of these structures is also confirmed by calculating the phonon band structures. The corresponding structural parameters are found in good agreement with experimental values. Furthermore, we present the bader charge analysis and optical properties of these phases.

  • 325. Kaewmaraya, Thanayut
    et al.
    De Sarkar, Abir
    Sa, Baisheng
    Sun, Z.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Department of Physics and Astronomy, Uppsala University.
    Strain-induced tunability of optical and photocatalytic properties of ZnO mono-layer nanosheet2014Inngår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 91, s. 38-42Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Strain-induced tunability of several properties of ZnO monolayer nanosheet has been systematically studied using density functional theory. The band gap of the sheet varies almost linearly with uniaxial strain, while it shows a parabola-like behavior under homogeneous biaxial strain. Tensile strain reduces ionicity of Zn-O bonds, while compressive strain increases it. This provides ample implications for the photocatalytic dissociation of water molecules and the scission of polar molecules on ZnO nanosheet. The dynamical stability of the sheet assessed by the calculation of its vibrational frequencies has shown the sheet to be unstable for 10% and 7.5% compressive biaxial homogeneous strain.

  • 326. Kaewmaraya, Thanayut
    et al.
    Luo, Wei
    Yang, Xiao
    Panigrahi, Puspamitra
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden.
    A new, layered monoclinic phase of Co3O4 at high pressure2015Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, nr 30, s. 19957-19961Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present the crystal structures and electronic properties of a Co3O4 spinel under high pressure. Co3O4 undergoes a first-order transition from a cubic (CB) Fd (3) over barm to a lower-symmetry monoclinic (MC) P2(1)/c phase at 35 GPa, occurring after the local high-spin to low-spin phase transition. The high-pressure phase exhibits the octahedral coordination of Co(II) and Co(III), whereas the CB phase contains the fourfold coordination of Co(II) and the sixfold coordination of Co(III). The CB-to-MC transition is attributed to the charge-transfer between the di-and trivalent cations via the enhanced 3d-3d interactions.

  • 327. Kanchana, V.
    et al.
    Vaitheeswaran, G.
    Alouani, M.
    Delin, Anna
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Electronic structure and x-ray magnetic circular dichroism of Sr2FeMoO6: Ab initio calculations2007Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, nr 22Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Theoretical investigations of the electronic structure, x-ray absorption, and x-ray magnetic circular dichroism (XMCD) at the Fe L-2,L-3 and Mo L-2,L-3 edges of Sr2FeMoO6 are carried out by means of the generalized gradient approximation. The magnetic coupling between Fe and Mo is found to be antiparallel, which gives direct confirmation of ferrimagnetic ordering and settles controversies existing between the earlier experimental reports. This is also confirmed by our good agreement of the Mo L-2,L-3 edges with experiment. Using our theoretical spectra, we recalculate the spin and orbital magnetic moments by means of the XMCD sum rules and compare the results with a direct self-consistent calculation and experiment.

  • 328. Kanchana, V.
    et al.
    Vaitheeswaran, G.
    Svane, A.
    Delin, Anna
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    First-principles study of elastic properties of CeO2, ThO2 and PoO22006Inngår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 18, nr 42, s. 9615-9624Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Using first-principles density functional calculations, the structural and elastic properties of fluorite type oxides CeO2, ThO2 and PoO2 were studied by means of the full-potential linear muffin-tin orbital method. Calculations were performed within the local density approximation (LDA) as well as generalized gradient approximation (GGA) to the exchange correlation potential. The calculated equilibrium lattice constants and bulk moduli are in good agreement with the experimental results, as are the computed elastic constants for CeO2 and ThO2. For PoO2 this is the first quantitative theoretical prediction of the ground state properties, and it still awaits experimental confirmation. The calculations find PoO2 to be a semiconductor with an indirect band gap and elastic constants similar in magnitude to those of CeO2 and ThO2.

  • 329.
    Kanchana, Venkatakrishnan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vaitheeswaran, Ganapathy
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ma, Yanming
    Xie, Yu
    Svane, A.
    Eriksson, O.
    Density functional study of elastic and vibrational properties of the Heusler-type alloys Fe2VAl and Fe2VGa2009Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 80, nr 12, s. 125108-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The structural and elastic properties as well as phonon-dispersion relations of the Heusler-type alloys Fe2VAl and Fe2VGa are computed using density functional and density-functional perturbation theory within the generalized-gradient approximation. The calculated equilibrium lattice constants agree well with the experimental values. The elastic constants of Fe2VAl and Fe2VGa are predicted. From the elastic constants the shear modulus, Young's modulus, Poisson's ratio, sound velocities, and Debye temperatures are obtained. By analyzing the ratio between the bulk and shear moduli, we conclude that both Fe2VAl and Fe2VGa are brittle in nature. The computed phonon-dispersion relation shows that both compounds are dynamically stable in the L2(1) structure without any imaginary phonon frequencies. The isomer shifts in Fe in the two compounds are discussed in terms of the Fe s partial density of states, which reveal larger ionicity/less hybridization in Fe2VGa than in Fe2VAl. For the same reason the Cauchy pressure is negative in Fe2VAl but positive in Fe2VGa.

  • 330. Kanhere, P.
    et al.
    Nisar, J.
    Tang, Y.
    Pathak, B.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Zheng, J.
    Chen, Z.
    Electronic structure, optical properties, and photocatalytic activities of LaFeO 3-NaTaO 3 solid solution2012Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, nr 43, s. 22767-22773Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A solid solution photocatalyst, Na 1-xLa xFe 1-xTa xO 3 (x up to 0.06), was prepared by the conventional solid-state method. The photophysical properties of the samples were studied by various experimental techniques and the electronic structures were investigated by using screened hybrid density functional (HSE06) calculations. The solid solution photocatalyst showed absorption of visible light extending up to 450 nm. Upon loading of platinum nanoparticles cocatalyst, the photocatalytic hydrogen evolution of 0.81 μ·mol·h -1·g -1 was obtained for 2% doping of LaFeO 3 in NaTaO 3, under visible radiation (λ > 390 nm; 20% methanol solution). The photocatalytic properties of the solid solution were found to be better than Fe doped NaTaO 3 compounds on account of the suitable band structure. The electronic structure analysis revealed that, in the case of Fe doping at the Ta site, unoccupied electronic states in between the band gap appear that are responsible for the visible-light absorption. However, in the case of La and Fe codoping (passivated doping) the mid-gap electronic states are completely filled, which makes the band structure suitable for the visible-light photocatalysis. The present solid solution of perovskites (LaFeO 3 and NaTaO 3) sheds light on the interesting photophysical properties and photocatalytic activities which could be beneficial for the photocatalysts derived from these compounds.

  • 331. Kanhere, Pushkar
    et al.
    Chakraborty, Sudip
    Rupp, Caroline J.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Condensed Matter Theory Group, Department of Physics and Astronomy, Uppsala University, Sweden.
    Chen, Zhong
    Substitution induced band structure shape tuning in hybrid perovskites (CH3NH3Pb1-xSnxI3) for efficient solar cell applications2015Inngår i: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 5, nr 130, s. 107497-107502Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Organic-inorganic hybrid perovskite compounds such as CH3NH3PbI3 hold a great potential for low cost photovoltaic devices. Though CH3NH3PbI3 possesses fundamental properties favorable for solar energy harvesting, environmentally safe materials with higher energy efficiency are needed for practical applications. Replacement of lead by tin is a promising solution and investigating the fundamental properties of lead and tin mixed halides is essential. In this article, we have reported electronic and optical properties by employing Density Functional Theory based first principles calculations of Sn doped methyl ammonium lead halide, CH3NH3Pb1-xSnxI3 (x = 0, 0.25, 0.5, 0.75, 1.0). Our results reveal that tin doping narrows the optical band gap allowing absorption of visible light up to 850 nm. Tin doping at Pb sites primarily affects the composition and nature of the valence band maximum. Tin 5p induced electronic states are highly delocalized in nature and are likely to improve the mobility and possible exciton diffusion lengths of holes. Based on the results of this study, 50% Sn doping could to be useful for enhanced performance of perovskite based photovoltaics.

  • 332. Kanhere, Pushkar
    et al.
    Shenai, Prathamesh
    Chakraborty, Sudip
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Condense Matter Theory Group, Department of Physics and Astronomy, Uppsala University.
    Zheng, Jianwei
    Chen, Zhong
    Mono- and co-doped NaTaO3 for visible light photocatalysis2014Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, nr 30, s. 16085-16094Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Electronic structures of doped NaTaO3 compounds are of significant interest to visible light photocatalysis. This work involves the study of the band gap, band edge potentials, and thermodynamic stability of certain mono-doped and co-doped NaTaO3 systems, using DFT-PBE as well as hybrid (PBE0) functional calculations. Doping of certain non-magnetic cations (Ti, V, Cu, Zn, W, In, Sn, Sb, Ce, and La), certain anions (N, C, and I), and certain co-dopant pairs (W-Ti, W-Ce, N-I, N-W, La-C, Pb-I, and Cu-Sn) is investigated. Our calculations suggest that substitutional doping of Cu at the Ta site, Cu at the Na site, and C at the O site narrows the band gap of NaTaO3 to 2.3, 2.8, and 2.1 eV, respectively, inducing visible light absorption. Additionally, passivated co-doping of Pb-I and N-W narrows the band gap of NaTaO3 to the visible region, while maintaining the band potentials at favorable positions. Hybrid density of states (DOS) accurately describe the effective band potentials and the location of mid-gap states, which shed light on the possible mechanism of photoexcitation in relation to the photocatalysis reactions. Furthermore, the thermodynamic stability of the doped systems and defect pair binding energies of co-doped systems are discussed in detail. The present results provide useful insights into designing new photocatalysts based on NaTaO3.

  • 333.
    Kapilashrami, Mukes
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Xu, Jun
    Biswas, Anis
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Tamaki, Takahiko
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Sharma, P.
    Rao, K. Venkat
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Belova, Lyuba
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Coexistence of ultraviolet photo-response and room-temperature ferromagnetism in polycrystalline ZnO thin films2010Inngår i: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, ISSN 0167-577X, Vol. 64, nr 11, s. 1291-1294Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The coexistence of ultraviolet (UV) photoconductivity (PC) and room-temperature ferromagnetism (RTFM) is observed in polycrystalline ZnO thin films deposited by unbalanced magnetron sputtering under high oxygen pressure. A significant increase in PC (similar to 870% to 40000%) is observed with increasing film thickness and the consequent structural disorder and film porosity. In contrast, the saturation magnetization (M(S)) at room temperature is found to decrease from 1.02 emu/g to 0.53 emu/g with increasing film thickness from 50 to 150 nm.

  • 334.
    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 theory2018Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, nr 14, artikkel-id 140504Artikkel i tidsskrift (Fagfellevurdert)
    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

  • 335.
    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 bismuth2019Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, nr 17, artikkel-id 174506Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 336. Khmelevska, T.
    et al.
    Khmelevskyi, S.
    Ruban, Andrei V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Mohn, P.
    Dependence of magnetism of VAu4 alloy on the state of chemical order: A first principles study2007Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 76, nr 5Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The strong dependence of the magnetic properties of the alloy VAu4 upon the degree of chemical order has been a subject of intense experimental studies and controversial theoretical interpretations. In the framework of density functional theory using the coherent potential approximation embodied in the Korringa-Kohn-Rostoker method, we perform first principles calculations of VAu4 varying the degree of atomic chemical order from a disordered fcc alloy to the fully ordered MoNi4-type structure. In contrast to the conventional point of view, partially also based on earlier first principles studies of the ordered structure, our results suggest a localized character of the vanadium moments rather than being weakly itinerant. Moreover, we find that in the fully ordered alloy an antiferromagnetic state is more stable than the ferromagnetic. This finding leads to a significant revision of the earlier descriptions of magnetism in VAu4, which were based either on itinerant or local moment pictures. Investigating fcc Au-V alloys richer in vanadium, we also study the role of local environment effects on the stabilization of the magnetic moments at the V atoms and advocate a ferrimagnetic character of the experimentally observed state with a small spontaneous magnetization.

  • 337. Khmelevska, T.
    et al.
    Khmelevskyi, S.
    Ruban, Andrei V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Mohn, P.
    Magnetism and origin of non-monotonous concentration dependence of the bulk modulus in Fe-rich alloys with Si, Ge and Sn: a first-principles study2006Inngår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 18, nr 29, s. 6677-6689Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Using the first-principles calculations based on the coherent potential approximation, we study the electronic structure, magnetic moments and the bulk modulus of FeX alloys with IVB group elements ( X = Si, Ge, Sn) in the Fe-rich concentration range (x = 0.0 - 0.25), which form a stability region of bcc-related phases. In agreement with experiment, our calculations reproduce well a peculiar non-monotonous behaviour of the bulk modulus in Fe - Si alloys with increasing Si concentration. Such a dependence is found for all bcc-related disordered and partially ordered Fe - Si phases A2, B2 and D0(3), which is in contrast with an earlier suggestion that the non-monotonous bulk modulus behaviour is related to partial ordering in Fe - Si. In addition, our results predict a similar behaviour in Fe - Ge and Fe - Sn alloys. It is shown that the observed behaviour of the bulk modulus is entirely related to the changes of the magnetic properties with chemical composition.

  • 338. Khmelevskuyi, S.
    et al.
    Ruban, Andrei V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Mohn, P.
    Frustrated magnetism in superconducting hexagonal Fe: Calculation of inter-atomic pair exchange interactions2007Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 460, s. 647-648Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We calculate magnetic exchange interaction parameters in hcp Fe using magnetic force theorem in density functional theory in a range of volumes, which covers the region of stability of the superconducting state. The calculations are done for a paramagnetic state using disordered local moment model within a local fixed spin-moment constraint. It is found that exchange interaction parameters strongly favor antiferromagnetic inter-plane stacking of the basal hcp planes. At the same time, the nearest neighbor in-plane exchange interaction parameters are also strongly antiferromagnetic, which should lead to magnetic frustrations in the planar triangular lattice. Eventual consequences of the magnetic frustration effects on the interplay between magnetism and superconductivity in hcp Fe under pressure are discussed.

  • 339. Khmelevskyi, S.
    et al.
    Khmelevska, T.
    Ruban, Andrei V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Mohn, P.
    Magnetic exchange interactions in the paramagnetic state of hcp Gd2007Inngår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 19, nr 32Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We use the first-principles magnetic force theorem embodied in the Korringa-Kohn-Rostoker method to calculate pair magnetic exchange interactions in pure hexagonal close packed ( hcp) Gd metal in the ferromagnetic as well as in the paramagnetic state with disordered local 4f-moments. It is found that the exchange interactions between the localized 4f-moments, in particular also distant ones, depend on the state of magnetic disorder. Such a dependence is a consequence of the electronic structure changes of the conduction band that mediates the interaction between the local moments. The magnetic ordering temperature has been calculated using a Monte Carlo simulation technique and the results are compared with mean-field based studies.

  • 340. Khmelevskyi, S.
    et al.
    Ruban, Andrei V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kakehashi, Y.
    Mohn, P.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ab initio investigation of the Invar anomaly in ordered fcc Fe-Pt alloys2005Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, nr 6Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The magnetovolume anomaly in ordered fcc Fe-Pt Invar alloys is studied by ab inito Korringa-Kohn-Rostoker atomic-sphere approximation technique in the framework of density-functional theory. The paramagnetic state above the magnetic ordering transition temperature is treated using the disordered local moment (DLM) approach. We show that the DLM approach is able to describe and explain the Invar anomaly in ordered Fe-rich Fe-Pt alloys similarly to our previous work for the disordered modification. In particular, our calculations predict the weakening of the Invar anomaly in chemically ordered compositions as compared to the disordered case as well as a decreasing magnetovolume anomaly with increasing Pt concentrations for both ordered and disordered cases in full agreement with experimental observations. The detailed study of the Fe3Pt compound with varying chemical long-range order has revealed a continuously decreasing spontaneous volume magnetostriction with increasing degree of order. This can be understood from the corresponding band structure of random and ordered alloys.

  • 341. Khmelevskyi, S.
    et al.
    Ruban, Andrei V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Mohn, P.
    Electronic structure analysis of the pressure induced metamagnetic transition and magnetovolume anomaly in Fe3C - Cementite2005Inngår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 17, nr 46, s. 7345-7352Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Within the framework of ab initio electronic structure calculations we study a mechanism for the recently discovered pressure induced metamagnetic transition in Fe3C-cementite. It is shown that the transition occurs between a high moment ferromagnetic state and a non-magnetic (non-spin-polarized) state without stabilization of any intermediate antiferromagnetic-like state, which may explain the experimentally observed difference in character of the transitions in Fe3C and fcc Fe-Pt. Although both materials are Invar-type systems we find considerable differences between their electronic structures and the degrees of localization, or itinerancy, of the Fe magnetic moments. The possibilities for describing the thermal expansion anomaly in Fe3C within existing approaches to the Invar problem are discussed in detail.

  • 342.
    Kholmatov, Shavkat
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    On Some Positive Effects of the Swirl on Fluid Flow and Heat Transfer During Mould Filling2009Doktoravhandling, med artikler (Annet vitenskapelig)
  • 343.
    Khossossi, Nabil
    et al.
    Moulay Ismail Univ, Fac Sci, Dept Phys, LP2MS,Unite Associee CNRST URAC 08, BP 11201, Meknes, Morocco.;Uppsala Univ, Dept Phys & Astron, Condensed Matter Theory Grp, S-75120 Uppsala, Sweden..
    Banerjee, Amitava
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Benhouria, Younes
    Moulay Ismail Univ, Fac Sci, Dept Phys, LP2MS,Unite Associee CNRST URAC 08, BP 11201, Meknes, Morocco..
    Essaoudi, Ismail
    Moulay Ismail Univ, Fac Sci, Dept Phys, LP2MS,Unite Associee CNRST URAC 08, BP 11201, Meknes, Morocco.;Uppsala Univ, Dept Phys & Astron, Condensed Matter Theory Grp, S-75120 Uppsala, Sweden..
    Ainane, Abdelmajid
    Moulay Ismail Univ, Fac Sci, Dept Phys, LP2MS,Unite Associee CNRST URAC 08, BP 11201, Meknes, Morocco.;Uppsala Univ, Dept Phys & Astron, Condensed Matter Theory Grp, S-75120 Uppsala, Sweden.;Max Planck Inst Phys Complexer Syst, NothnitzerStr 38, D-01187 Dresden, Germany..
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala Univ, Dept Phys & Astron, Condensed Matter Theory Grp, S-75120 Uppsala, Sweden..
    Ab initio study of a 2D h-BAs monolayer: a promising anode material for alkali-metal ion batteries2019Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 21, nr 33, s. 18328-18337Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The selection of a suitable two dimensional anode material is one of the key steps in the development of alkali metal ion batteries to achieve superior performance with an ultrahigh rate of charging/discharging capability. Here, we have used state of the art density functional theory (DFT) to explore the feasibility of two dimensional (2D) honeycomb boron arsenide (h-BAs) as a potential anode for alkali-metal (Li/Na/K)-ion batteries. The structural and dynamic stability has been confirmed from the formation energy and the non-negative phonon frequency. The h-BAs monolayer exhibits negative adsorption-energy values of -0.422, -0.321 and -0.814 eV, for the Li, Na, and K-ions, respectively. Subsequently, during the charging process the adsorption-energy increases considerably without an energy-barrier when any of the A-atoms achieve a crucial distance (similar to 8 angstrom). In addition, it has been observed that insertion of the mono alkali metal atom into the h-BAs surface results in the semi-conducting nature of the monolayer being transformed into a metallic-state. The low energy barriers for Li (0.522 eV), Na (0.248), and K (0.204 eV) active ion migration imply high diffusion over the h-BAs surface, hence suggesting it has a high charge/discharge capability. Moreover, we have obtained low average operating voltages of 0.49 V (Li), 0.35 V (Na) and 0.26 V (K) and high theoretical capacities of 522.08 mA h g(-1) (for Li and Na) and 209.46 mA h g(-1) (for K) in this study. The aforementioned findings indicate that a h-BAs monolayer could be a promising anode material in the search for low cost and high performance alkali metal ion batteries.

  • 344. Kim, D. Y.
    et al.
    Scheicher, R. H.
    Mao, H. K.
    Kang, T. W.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    General trend for pressurized superconducting hydrogen-dense materials2010Inngår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 107, nr 7, s. 2793-2796Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The long-standing prediction that hydrogen can assume a metallic state under high pressure, combined with arguments put forward more recently that this state might even be superconducting up to high temperatures, continues to spur tremendous research activities toward the experimental realization of metallic hydrogen. These efforts have however so far been impeded by the enormous challenges associated with the exceedingly large required pressure. Hydrogen-dense materials, of the MH4 form ( where M can be, e. g., Si, Ge, or Sn) or of the MH3 form ( with M being, e. g., Al, Sc, Y, or La), allow for the rather exciting opportunity to carry out a proxy study of metallic hydrogen and associated high-temperature superconductivity at pressures within the reach of current techniques. At least one experimental report indicates that a superconducting state might have been observed already in SiH4, and several theoretical studies have predicted superconductivity in pressurized hydrogen-rich materials; however, no systematic dependence on the applied pressure has yet been identified so far. In the present work, we have used first-principles methods in an attempt to predict the superconducting critical temperature (T-c) as a function of pressure ( P) for three metal-hydride systems of the MH3 form, namely ScH3, YH3, and LaH3. By comparing the obtained results, we are able to point out a general trend in the T-c-dependence on P. These gained insights presented here are likely to stimulate further theoretical studies of metallic phases of hydrogen-dense materials and should lead to new experimental investigations of their superconducting properties.

  • 345. Kim, D. Y.
    et al.
    Srepusharawoot, P.
    Pickard, C. J.
    Needs, R. J.
    Bovornratanaraks, T.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Pinsook, U.
    Phase stability and superconductivity of strontium under pressure2012Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 101, nr 5, s. 052604-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have used the ab initio random structure searching method together with density functional theory calculations to find stable structures of strontium under pressures up to 50 GPa. We predict a sequence of structural phase transitions and the stability of an orthorhombic structure of Cmcm symmetry above 25 GPa. Our energy, lattice dynamics, and molecular dynamics calculations confirm the stability of the Cmcm structure. The electron-phonon coupling calculations show that superconductivity arises in the bcc structure of compressed Sr and that it continues to exist in the Cmcm structure. The calculated superconducting transition temperatures are in good agreement with experiment. Our study gives an excellent account of the experimental observations.

  • 346.
    Kim, Do-Kyung
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Hong, J.
    Origin of thickness dependent spin reorientation transition of B2 type FeCo alloy films2013Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 114, nr 21, s. 213911-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have investigated the origin of thickness dependent spin reorientation transition (SRT) of B2 type FeCo alloy using the full potential linearized augmented plane wave method. It has been reported that FeCo alloy films on various substrates show a SRT from perpendicular to in-plane magnetization at an approximate thickness of 15 monolayers (MLs). The enhanced perpendicular magnetic anisotropy in bulk FeCo is attributed to a tetragonal distortion. However, we have found that the tetragonal distortion tends to suppress the magnetocrystalline anisotropy (MCA) energy at increasing film thickness in two-dimensional structure. In contrast, the magnitude of the shape anisotropy energy increases at increasing FeCo film thickness. Interestingly, the shape anisotropy overcomes the MCA and the SRT, from perpendicular anisotropy to in-plane magnetization, which occurs at a thickness of 15 ML. Consequently, we are able to clearly understand the physical mechanism of the thickness dependent SRT in terms of the competing reactions of these two counteracting contributions.

  • 347.
    Kim, Dongyoo
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Hong, Jisang
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden; Wigner Research Center for Physics, Hungary.
    Epitaxial strain and composition-dependent magnetic properties of MnxGa1-x alloys2014Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, nr 14, s. 144413-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Using first-principles calculation, we have investigated the structural and magnetic properties of MnxGa1-x alloys with Mn content (x) changing from 0.5 to 0.75 in step of x = 0.125. The MnxGa1-x systems crystallize in tetragonal structures, and the tetragonal ratio (c/a) is strongly influenced by chemical composition. The in-plane lattice constants (a) show very weak concentration dependence, but the lattice parameters along the z axis (c) are significantly modified by x. We have found that the magnetic properties of MnxGa1-x alloys are strongly affected by the Mn content and the epitaxial strain. Very interestingly, the magnetocrystalline anisotropy (MCA) of MnxGa1-x alloys follows totally different behaviors with x and epitaxial strain. An especially wide range of MCA values are obtained by straining the Mn0.5Ga0.5 alloy. The spin polarization (at the Fermi level) of Mn0.75Ga0.25 has been calculated from 44% to 57% with epitaxial strain.

  • 348.
    Kim, Dongyoo
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden; Wigner Research Center for Physics, Hungary.
    Tuned Magnetic Properties of L1(0)-MnGa/Co(001) Films by Epitaxial Strain2016Inngår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, artikkel-id 19508Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We demonstrate that the interface structure has a significant influence on the magnetic state of MnGa/Co films consisting of L1(0)-MnGa on face-centered-cubic Co(001) surface. We reveal an antiferromagnetic to ferromagnetic magnetization reversal as a function of the lateral lattice constant. The magnetization reversal mainly originates from localized states and weak hybridization at interface due to charge redistribution between muffin-tin spheres and interstitial region. The magnetic anisotropy energy of Mn/Co interface system is enhanced with increasing in-plane lattice constant, which is ascribed to the interface interactions and the above magnetization reversal.

  • 349. Kissavos, A. E.
    et al.
    Shallcross, S.
    Kaufman, L.
    Granas, O.
    Ruban, Andrei V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Abrikosov, I. A.
    Thermodynamics of ordered and disordered phases in the binary Mo-Ru system2007Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, nr 18Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have performed ab initio calculations of the mixing enthalpy for the Mo-Ru alloy system. Both completely random alloys on the fcc, bcc, and hcp lattices as well as ordered and partially ordered structures based on the hcp lattice and a sigma phase have been examined. Further, we have performed a ground-state search for the Ru-rich region using ab initio derived effective interactions, and find a series of structures below the tie line of the simple compounds. Using the structures from this ground-state search, we are able to make an estimation of the contribution to the total energy due to ordering effects in this system. We find unusually large deviations between calculated and experimental values of the mixing enthalpy for Ru-rich hcp alloys. Our calculations indicate, in agreement with experiment, that there are ordering trends in the system. However, even under assumption of maximal order theoretical results differ substantially from the experiment. Possible reasons for the disagreement are discussed.

  • 350. Kissavos, A. E.
    et al.
    Simak, S. I.
    Olsson, Pär
    Department of Neutron Research, Ångström Laboratory, Uppsala University.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Abrikosov, I. A.
    Total energy calculations for systems with magnetic and chemical disorder2006Inngår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 35, nr 1, s. 1-5Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The accuracy of the exact muffin-tin orbitals method combined with the coherent potential approximation (EMTO-CPA) for total energy calculations for systems with magnetic and chemical disorder, which is present simultaneously, is investigated. The mixing enthalpy of ordered, as well as disordered FeCo, FeNi, and FeCu equiatomic ferromagnetic alloys is calculated with the EMTO-CPA method and with the full-potential projector augmented wave (PAW) method. The results are compared and found to be in excellent agreement with each other. The EMTO-CPA method, in combination with disordered local moment model, is then applied to calculate the mixing enthalpy of the random paramagnetic face-centered cubic (fcc) FeCo alloy, as well as body-centered cubic (bcc) FeCr and FeV alloys over the whole concentration range. The results are compared with experimental data and a very good agreement is found again.

45678910 301 - 350 of 922
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf