uu.seUppsala University Publications
Change search
Refine search result
3456789 251 - 300 of 551
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 251. Kulkarni, Shrinivas R.
    et al.
    Vennila, R. Selva
    Phatak, Nishad A.
    Saxena, S. K.
    Zha, C. S.
    El-Raghy, T.
    Barsoum, M. W.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Study of Ti2SC under compression up to 47 GPa2008In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 448, no 1-2, p. L1-L4Article in journal (Refereed)
    Abstract [en]

    The pressure dependence of the lattice parameters of the ternary layered carbide, Ti2SC, was measured by using synchrotron radiation X-ray diffraction and a diamond anvil cell setup. The experiment was conducted at room temperature and no phase transformation was observed up to the maximum pressure of 47 GPa. The a and c lattice parameters at room condition are 3.216 (A) over circle and 11.22 (A) over circle, respectively. The bulk modulus, calculated using the Birch-Murnaghan equation of state, is 191 +/- 3 GPa, with a pressure derivative of 4.0 +/- 0.3 and that obtained by our ab initio calculations is 183 GPa, with a pressure derivative of 4.1. L Like the majority of the ternary layered carbides (MAX phases), compressibility along the c-axis was higher than that along the a-axis.

  • 252.
    Kwon, S. K.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Nabi, Z.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Kádas, Krisztina
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Kollar, J.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Surface Energy and Stress Release by Layer Relaxation2005In: Physical Review B, Vol. 72, p. 235423-Article in journal (Refereed)
    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 ~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.

  • 253.
    Kádas, Krisztina
    et al.
    Applied Materials Physics, Department of Materials Science and Engineering, The Royal Institute of Technology, Stockholm.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Thermo-physical properties of body-centered cubic iron-magnesium alloys under extreme conditions2011In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 151, no 3, p. 203-207Article in journal (Refereed)
    Abstract [en]

    Using density functional theory formulated within the framework of the exact muffin-tin orbitals method, we investigate the thermo-physical properties of body-centered cubic (bcc) iron-magnesium alloys, containing 5 and 10 atomic % Mg, under extreme conditions, at high pressure and high temperature. The temperature effect is taken into account via the Fermi-Dirac distribution of the electrons. We find that at high pressures pure bcc iron is dynamically unstable at any temperature, having a negative tetragonal shear modulus (C’). Magnesium alloying significantly increases C’ of Fe, and bcc Fe-Mg alloys become dynamically stable at high temperature. The electronic structure origin of the stabilization effect of Mg is discussed in detail. We show that the thermo-physical properties of a bcc Fe-Mg alloy with 5% Mg agree well with those of the Earth’s inner core as provided by seismic observations.

  • 254. Kádas, Krisztina
    et al.
    Nabi, Z.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Kwon, S. K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Kollar, J.
    Surface relaxation and surface stress of $4d$ transition metals2006In: Surface Science, Vol. 600, p. 395-402Article in journal (Refereed)
  • 255.
    Kádas, Krisztina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Elastic properties of iron-rich hcp Fe-Mg alloys up to Earth's core pressures2008In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 271, no 1-4, p. 221-225Article in journal (Refereed)
    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.

  • 256.
    Kádas, Krisztina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Theoretical evidence of a superconducting transition in doped silicon and germanium driven by a variation of chemical composition2008In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 92, no 5, p. 052505-Article in journal (Refereed)
    Abstract [en]

    We present the first theoretical evidence of chemical composition driven superconductivity in acceptor-doped silicon and germanium, using density functional theory. We examine the concentration dependence of T-c in B-doped Si and Ge and predict that B-doped Ge is a superconductor with a slightly higher T-c than B-doped Si. We show that there is a critical concentration above which B-doped Si and Ge become superconducting and estimate it to be similar to 2.6% in Si:B and similar to 2.2% in Ge:B. Considering the Al-doped Si and Ge, we point out the decisive role of the chemical element in the hole-doping scenario.

  • 257.
    Kádas, Krisztina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Johansson, Borje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Kollar, Janos
    Temperature dependent elastic properties of alpha-beryllium from first principles2007In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 76, no 23, p. 235109-Article in journal (Refereed)
    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.

  • 258.
    Kádas, Krisztina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Stability of body-centered cubic iron-magnesium alloys in the Earth's inner core2009In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 106, no 37, p. 15560-15562Article in journal (Refereed)
    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.

  • 259.
    Lai, Qiwen
    et al.
    Univ New S Wales, Sch Chem Engn, MERLin Grp, Sydney, NSW 2052, Australia..
    Paskevicius, Mark
    Aarhus Univ, Dept Chem, DK-8000 Aarhus, Denmark.;Aarhus Univ, iNANO, DK-8000 Aarhus, Denmark.;Curtin Univ, Dept Phys Astron & Med Radiat Sci, Bentley, WA 6102, Australia..
    Sheppard, Drew A.
    Curtin Univ, Dept Phys Astron & Med Radiat Sci, Bentley, WA 6102, Australia..
    Buckley, Craig E.
    Curtin Univ, Dept Phys Astron & Med Radiat Sci, Bentley, WA 6102, Australia..
    Thornton, Aaron W.
    CSIRO, Clayton, Vic 3169, Australia..
    Hill, Matthew R.
    CSIRO, Clayton, Vic 3169, Australia..
    Gu, Qinfen
    Australian Synchrotron, Clayton, Vic 3168, Australia..
    Mao, Jianfeng
    Univ Wollongong, Inst Superconducting & Elect Mat, Wollongong, NSW 2500, Australia..
    Huang, Zhenguo
    Univ Wollongong, Inst Superconducting & Elect Mat, Wollongong, NSW 2500, Australia..
    Liu, Hua Kun
    Univ Wollongong, Inst Superconducting & Elect Mat, Wollongong, NSW 2500, Australia..
    Guo, Zaiping
    Univ Wollongong, Inst Superconducting & Elect Mat, Wollongong, NSW 2500, Australia..
    Banerjee, Amitava
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Chakraborty, Sudip
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Aguey-Zinsou, Kondo-Francois
    Univ New S Wales, Sch Chem Engn, MERLin Grp, Sydney, NSW 2052, Australia..
    Hydrogen Storage Materials for Mobile and Stationary Applications: Current State of the Art2015In: ChemSusChem, ISSN 1864-5631, E-ISSN 1864-564X, Vol. 8, no 17, p. 2789-2825Article in journal (Refereed)
    Abstract [en]

    One of the limitations to the widespread use of hydrogen as an energy carrier is its storage in a safe and compact form. Herein, recent developments in effective high-capacity hydrogen storage materials are reviewed, with a special emphasis on light compounds, including those based on organic porous structures, boron, nitrogen, and aluminum. These elements and their related compounds hold the promise of high, reversible, and practical hydrogen storage capacity for mobile applications, including vehicles and portable power equipment, but also for the large scale and distributed storage of energy for stationary applications. Current understanding of the fundamental principles that govern the interaction of hydrogen with these light compounds is summarized, as well as basic strategies to meet practical targets of hydrogen uptake and release. The limitation of these strategies and current understanding is also discussed and new directions proposed.

  • 260.
    Larsson, Peter
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Liivat, Anti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Structural Chemistry.
    Thomas, John O.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Structural Chemistry.
    Structural and electrochemical aspects of Mn substitution into Li2FeSiO4 from DFT calculations2010In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 47, no 3, p. 678-684Article in journal (Refereed)
    Abstract [en]

    DFT calculations are presented which probe the effect of low-concentration Mn substitution of the Fe-sites in Li2FeSiO4: the promising new and potentially cheap cathode material for upscaled Li-ion battery applications. The LixFe0.875Mn0.125SiO4 System investigated could be achieved by replacing 12.5% of the Fe-sites in 2 x 2 x 1 and 2 x 2 x 2 supercells by Mn ions. The evolution of Bader charges and partial densities of states (DOS) have been followed under a stepwise delithiation process. A clear structural distortion is seen to occur at the Mn-site on delithiation, suggesting possible structural instability. Oxidation of Mn beyond 3+ is calculated to occur at potentials in excess of 4.7 V, implying that oxidation of well separated (>10 angstrom) low-concentration Mn ions to Mn4+ is energetically unfavourable in the LixFe0.875Mn0.125SiO4 structure. This, together with previous DFT results for higher levels of Mn substitution into Li2FeSiO4, indicates that capacity increase in Li2Fe1 (-) yMnySiO4 through a > 1 electron redox reaction may not be so readily attainable in practice, either for high or low Mn concentrations.

  • 261.
    Larsson, Peter
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Araujo, C. Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Larsson, J. Andrea
    Jena, Puru
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Role of catalysts in dehydrogenation of MgH2 nanoclusters2008In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 105, no 24, p. 8227-8231Article in journal (Refereed)
    Abstract [en]

    A fundamental understanding of the role of catalysts in dehydrogenation of MgH2 nanoclusters is provided by carrying out first-principles calculations based on density functional theory. It is shown that the transition metal atoms Ti, V, Fe, and Ni not only lower desorption energies significantly but also continue to attract at least four hydrogen atoms even when the total hydrogen content of the cluster decreases. In particular, Fe is found to migrate from the surface sites to the interior sites during the dehydrogenation process, releasing more hydrogen as it diffuses This diffusion mechanism may account for the fact that a small amount of catalysts is sufficient to improve the kinetics of MgH2. which is essential for the use of this material for hydrogen storage in fuel-cell applications.

  • 262.
    Larsson, Peter
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Araújo, C. Moysés
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Larsson, J. Andreas
    Jena, Puru
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Role of Catalyst in Dehydrogenation of MgH2 Nanoclusters2008In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 105, no 24, p. 8227-8231Article in journal (Refereed)
  • 263.
    Larsson, Peter
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Larsson, J. Andreas
    Tyndall National Institute.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ding, Feng
    Fysiska Institutionen, Göteborgs Universitet.
    Yakubson, Boris I.
    ME&MS Department, Rice University, Houston, Texas.
    Duan, Haiming
    Fysiska Institutionen, Göteborgs Universitet.
    Rosén, Arne
    Fysiska Institutionen, Göteborgs Universitet.
    Bolton, Kim
    School of Engineering, University College of Borås.
    Calculating carbon nanotube–catalyst adhesion strengths2007In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, no 11, p. 115419-Article in journal (Refereed)
    Abstract [en]

    Density-functional theory is used to assess the validity of modeling metal clusters as single atoms or rings of atoms when determining adhesion strengths between clusters and single-walled carbon nanotubes (SWNTs). Representing a cluster by a single atom or ring gives the correct trends in SWNT-cluster adhesion strengths (Fe ≈ Co > Ni), but the single-atom model yields incorrect minimum-energy structures for all three metals. We have found that this is because of directional bonding between the SWNT end and the metal cluster, which is captured in the ring model but not by the single atom. Hence, pairwise potential models that do not describe directional bonding correctly, and which are commonly used to study these systems, are expected to give incorrect minimum-energy structures.

  • 264. Lebegue, Sebastien
    et al.
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kim, Duck Young
    Ramzan, Muhammad
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Mao, Ho-kwang
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Semimetallic dense hydrogen above 260 GPa2012In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 109, no 25, p. 9766-9769Article in journal (Refereed)
    Abstract [en]

    Being the lightest and the most abundant element in the universe, hydrogen is fascinating to physicists. In particular, the conditions of its metallization associated with a possible superconducting state at high temperature have been a matter of much debate in the scientific community, and progress in this field is strongly correlated with the advancements in theoretical methods and experimental techniques. Recently, the existence of hydrogen in a metallic state was reported experimentally at room temperature under a pressure of 260-270 GPa, but was shortly after that disputed in the light of more experiments, finding either a semimetal or a transition to an other phase. With the aim to reconcile the different interpretations proposed, we propose by combining several computational techniques, such as density functional theory and the GW approximation, that phase III at ambient temperature of hydrogen is the Cmca-12 phase, which becomes a semimetal at 260 GPa. From phonon calculations, we demonstrate it to be dynamically stable; calculated electron-phonon coupling is rather weak and therefore this phase is not expected to be a high-temperature superconductor.

  • 265.
    Lebègue, Sébastien
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Araújo, C. Moysés
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Arnaud, B.
    Alouani, M.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Quasiparticle and optical properties of BeH22007In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 19, no 3, p. 036223-Article in journal (Refereed)
    Abstract [en]

    The quasiparticle and optical properties of BeH2 are computed by means of the all-electron GW approximation in conjunction with the projector augmented wave (PAW) method. The GW approximation, through the calculation of the self-energy and the optical dielectric function in the random phase approximation, shows that BeH2 is a large band gap insulator. The results are discussed in view of future experiments.

  • 266. Lee, J. -Y
    et al.
    Punkkinen, M. P. J.
    Univ Turku, Dept Phys & Astron, FI-20014 Turku, Finland.
    Schönecker, S.
    KTH Royal Inst Technol, Appl Mat Phys, Dept Mat Sci & Engn, SE-10044 Stockholm, Sweden.
    Nabi, Z.
    Univ Djillali Liabes Sidi Bel Abbes, Lab Catalysis & React Syst, Sidi Bel Abbes 22000, Algeria.
    Kádas, Krisztina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Wigner Res Ctr Phys, Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary.
    Zolyomi, V.
    Wigner Res Ctr Phys, Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary;Univ Manchester, Natl Graphene Inst, Manchester M13 9PL, Lancs, England.
    Koo, Y. M.
    Pohang Univ Sci & Technol, Grad Inst Ferrous Technol, Pohang 37673, South Korea.
    Hu, Q. -M
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Appl Mat Phys, Dept Mat Sci & Engn, SE-10044 Stockholm, Sweden.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Appl Mat Phys, Dept Mat Sci & Engn, SE-10044 Stockholm, Sweden.
    Kollar, J.
    Wigner Res Ctr Phys, Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary.
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Appl Mat Phys, Dept Mat Sci & Engn, SE-10044 Stockholm, Sweden;Wigner Res Ctr Phys, Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary.
    Kwon, S. K.
    Pohang Univ Sci & Technol, Grad Inst Ferrous Technol, Pohang 37673, South Korea.
    The surface energy and stress of metals2018In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 674, p. 51-68Article in journal (Refereed)
    Abstract [en]

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

  • 267. Lee, Jae-chul
    et al.
    Lee, Ji-eun
    Lee, Ju-won
    Lee, Jae-choon
    Subramaniam, N. G.
    Kang, Tae-won
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Se concentration dependent band gap engineering in ZnO1-xSex thin film for optoelectronic applications2014In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 585, p. 94-97Article in journal (Refereed)
    Abstract [en]

    ZnO1-xSex films with various selenium concentrations are deposited on the sapphire substrate (0001) by pulsed laser deposition technique. Structural properties of the thin films studied by X-ray diffraction (XRD) and chemical bonding studied by X-ray photoelectron spectroscopy (XPS) reveals that Se is substituted in O site during the growth of ZnO1-xSex films. Optical properties are analyzed by UV-Visible spectrometer. From the plot for (alpha h upsilon)(2) vs photon energy, it is inferred that the band gap energy of ZnO1-xSex gradually reduces to 2.85 eV with increasing Se concentration.

  • 268.
    Lee, Juwon
    et al.
    Dongguk Univ, QSRC, Seoul 100715, South Korea..
    Subramaniam, Nagarajan Ganapathi
    Dongguk Univ, QSRC, Seoul 100715, South Korea.;Dongguk Univ, Nano Informat Technol Acad, Seoul 100715, South Korea..
    Kowalik, Iwona Agnieszka
    Polish Acad Sci, Inst Phys, PL-02668 Warsaw, Poland..
    Nisar, Jawad
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Lee, Jaechul
    Dongguk Univ, QSRC, Seoul 100715, South Korea..
    Kwon, Younghae
    Dongguk Univ, QSRC, Seoul 100715, South Korea..
    Lee, Jaechoon
    Dongguk Univ, QSRC, Seoul 100715, South Korea..
    Kang, Taewon
    Dongguk Univ, QSRC, Seoul 100715, South Korea.;Dongguk Univ, Nano Informat Technol Acad, Seoul 100715, South Korea.;Hindustan Univ, Clean Energy & Nano Convergence Ctr CENCON, Madras 603103, Tamil Nadu, India..
    Peng, Xiangyang
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Arvanitis, Dimitri
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol KTH, Dept Mat & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden..
    Towards a new class of heavy ion doped magnetic semiconductors for room temperature applications2015In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, article id 17053Article in journal (Refereed)
    Abstract [en]

    The article presents, using Bi doped ZnO, an example of a heavy ion doped oxide semiconductor, highlighting a novel p-symmetry interaction of the electronic states to stabilize ferromagnetism. The study includes both ab initio theory and experiments, which yield clear evidence for above room temperature ferromagnetism. ZnBixO1-x thin films are grown using the pulsed laser deposition technique. The room temperature ferromagnetism finds its origin in the holes introduced by the Bi doping and the p-p coupling between Bi and the host atoms. A sizeable magnetic moment is measured by means of x-ray magnetic circular dichroism at the O K-edge, probing directly the spin polarization of the O(2p) states. This result is in agreement with the theoretical predictions and inductive magnetometry measurements. Ab initio calculations of the electronic and magnetic structure of ZnBixO1-x at various doping levels allow to trace the origin of the ferromagnetic character of this material. It appears, that the spin-orbit energy of the heavy ion Bi stabilizes the ferromagnetic phase. Thus, ZnBixO1-x doped with a heavy non-ferromagnetic element, such as Bi, is a credible example of a candidate material for a new class of compounds for spintronics applications, based on the spin polarization of the p states.

  • 269.
    Leifer, Klaus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Experimental Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Blom, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Jafri, Hassan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Löfås, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grigoriev, Anton
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Wallner, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Use of a nanoelectrode nanoparticle bridge platform in molecular electronics2010In: ElecMol’10, 5th International Meeting on Molecular Electronics, Grenoble, France, December 6-10, 2010, 2010, p. 116-116Conference paper (Refereed)
  • 270.
    Leifer, Klaus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Experimental Physics.
    Blom, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Experimental Physics.
    Jafri, S.Hassan M.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Experimental Physics.
    Welch, Ken
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Strömme, Maria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Löfås, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Grigoriev, Anton
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    FIB Fabrication and use of high resistance nanogaps for application in molecular electronics2010In: 17th International Microscopy Congress, IMC17, Brazil, 2010Conference paper (Refereed)
  • 271.
    Leifer, Klaus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Experimental Physics.
    Jafri, S.Hassan M.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Experimental Physics.
    Löfås, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Agustsson, J.
    University Basel, Department of Physics, CH-4056 Basel, Switzerland.
    Blom, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Experimental Physics.
    Grigoriev, Anton
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Fransson, J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Wallner, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    Calame, M.
    University Basel, Department of Physics, CH-4056 Basel, Switzerland.
    Vibrational signatures in inelastic tunneling spectroscopy from short molecule-nanoparticle chains trapped in versatile nanoelectrodesManuscript (preprint) (Other academic)
  • 272. Li, Bing
    et al.
    Ding, Yang
    Kim, Duck Young
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Zou, Guangtian
    Mao, Ho-Kwang
    Rhodium dihydride (RhH(2)) with high volumetric hydrogen density2011In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 108, no 46, p. 18618-18621Article in journal (Refereed)
    Abstract [en]

    Materials with very high hydrogen density have attracted considerable interest due to a range of motivations, including the search for chemically precompressed metallic hydrogen and hydrogen storage applications. Using high-pressure synchrotron X-ray diffraction technique and theoretical calculations, we have discovered a new rhodium dihydride (RhH(2)) with high volumetric hydrogen density (163.7 g/L). Compressing rhodium in fluid hydrogen at ambient temperature, the fcc rhodium metal absorbs hydrogen and expands unit-cell volume by two discrete steps to form NaCl-typed fcc rhodium monohydride at 4 GPa and fluorite-typed fcc RhH(2) at 8 GPa. RhH(2) is the first dihydride discovered in the platinum group metals under high pressure. Our low-temperature experiments show that RhH(2) is recoverable after releasing pressure cryogenically to 1 bar and is capable of retaining hydrogen up to 150 K for minutes and 77 K for an indefinite length of time.

  • 273.
    Li, Jibiao
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Unsaturated surface in CO saturation2017In: Surface and Interface Analysis, ISSN 0142-2421, E-ISSN 1096-9918, Vol. 49, no 9, p. 892-897Article in journal (Refereed)
    Abstract [en]

    In this paper, density functional theory calculations are used to address the puzzle of CO saturation on Fe(100). Through a comprehensive modeling of possible local configurations, we would be able to figure out a structural model for the CO-saturated Fe(100). The structural model is featured by forming a local structural motif of coupled on-top and hollow CO molecules. In this model, the on-top-bonded CO molecules pertain to critical couplings in the next neighbor spacing, which exclude all couplings below and above the next neighbor spacing. Rather than forming tilted on-top CO on the surface, the critical couplings align the on-top CO molecules in the perpendicular orientation. The new model with the coverage of 0.5ML yields even better X-ray emission and absorption spectra calculated by using density functional theory and shows consistent agreement with all previous experiments.

  • 274.
    Li, Jibiao
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Yangtze Normal Univ, Chongqing Key Lab Extraordinary Bond Engn & Adv M, Chongqing, Peoples R China; Stockholm Univ, AlbaNova Univ Ctr, Dept Phys, Stockholm, Sweden.
    He, Xin
    Sichuan Univ Arts & Sci, Sch Intelligent Mfg, Dazhou, Peoples R China.
    Peng, Cheng
    Yangtze Normal Univ, Chongqing Key Lab Extraordinary Bond Engn & Adv M, Chongqing, Peoples R China.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Chemical Bonding of Unique CO on Fe(100)2018In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 16, p. 9062-9074Article in journal (Refereed)
    Abstract [en]

    At low coverage, CO molecules are known to preferentially occupy the hollow sites of Fe(100) with considerably inclined molecular orientations. This CO configuration serves as the precursor state of CO dissociation, which is particularly important in several important catalytic reactions. In this study, we present a unique bonding picture of the precursor state from the spin, charge, and orbital perspectives. From the spin and orbital views, we show the antiferromagenetic nature of the adsorbate–metal coupling, where 2π magnetism prevails with a dominant spin-down channel. However, contrasting tendencies are found for the two 1π orbitals in two orthogonal directions: the 1π orbital in the vertical plane loses its symmetry, whereas the other 1π orbital remains intact with a preserved symmetry. The 1π symmetry in the vertical plane favors the 1π → 2π* excitation mechanism owing to the partial opening up of the 1π symmetry. In the charge perspective, we have identified a charge transfer mechanism involving the local structural IFeC–C–O motif, in which the surface slightly charges the adsorbate with additional partial electrons located at the surface Fe atoms bonded to the carbon end, whereas the charges of the metallic atoms beneath the IFeC–C–O motif are found to be depleted. In both the adsorbate and metal sides, the depletion of s electrons serves as a good measure of orbital repulsion and delocalization. Interestingly, the carbon and oxygen ends exhibit contrasting electron affinity with the metal surface: the carbon end is attractive, whereas the oxygen end is repulsive in terms of the contrasting charge rearrangement in the bonded metallic atoms.

  • 275.
    Li, Mingkai
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Hubei Univ, Wuhan, Peoples R China.
    Long, Debing
    Hubei Univ, Wuhan, Peoples R China.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    He, Yunbin
    Hubei Univ, Wuhan, Peoples R China.
    Magnetic order and phase diagram of magnetic alloy system: MgxNi1-xO alloy2017In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 254, no 9, article id 1700085Article in journal (Refereed)
    Abstract [en]

    The antiferromagnetic phase diagram of MgxNi1-xO alloy was reexamined theoretically by multicomponent cluster expansion method. It predicts antiferromagnetic state in the alloy with high Mg content, instead of a mixture of antiferromagnetic and paramagnetic states, which was deduced previously from neutron diffraction results. The theoretically found intermediate antiferromagnetic ground states at Mg contents of x(Mg) = 0.25 and 0.75 exhibit very low neutron diffraction intensities, which leads to confusion with paramagnetic state. Our approach here reduced remarkably the computation time in searching the intermediate ground states as well as calculating the magnetic phase diagram.

  • 276.
    Li, S.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Barsoum, M. W.
    Jena, P.
    Johansson, B.
    Optical properties of Ti3SiC2 and Ti4AlN32008In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 92, no 22, p. 221907-Article in journal (Refereed)
    Abstract [en]

    The dielectric functions of the MAX phases, Ti3SiC2 and Ti4AlN3, have been determined from first principles calculations. We compared the dielectric functions and the reflectivity spectra of Ti3SiC2 and Ti4AlN3 with those of TiC and TiN. The optical spectra were analyzed by means of the electronic structure, which provides theoretical understanding of the conduction mechanism of these two phases. We found that Ti4AlN3 can be used to avoid solar heating and also increase the radiative cooling due to the increased thermal emittance as compared to TiN. Ti4AlN3 can therefore be a candidate coating material for temperature control of space vehicles.

  • 277.
    Li, S.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ahuja, Rajeev
    Wang, Y.
    Johansson, Börje
    Crystallographic structures of PbWO42003In: High Pressure Research, Vol. 23, no 3, p. 343-Article in journal (Refereed)
  • 278. Li, S.
    et al.
    Jena, P.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Dehydrogenation Mechanism in Catalyst-activated MgH22006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, no 13, p. 132106-Article in journal (Refereed)
    Abstract [en]

    A small amount of Nb2O5 catalyst is known to substantially improve the desorption thermodynamics and kinetics of MgH2. Using density functional theory in combination with ab initio molecular dynamics simulation, we provide theoretical understanding of the mechanism of dehydrogenation in Nb doped MgH2. We show that the substitution of Nb at the Mg site followed by the clustering of H around Nb is a likely pathway for hydrogen desorption. We also find that dehydrogenation from the vicinity of Mg vacancies is exothermic. However, the vacancies are not likely to play a significant role in hydrogen desorption due to their high formation energy (3.87 eV).

  • 279.
    Li, S.
    et al.
    Physics Department, Virginia Commonwealth University, Richmond, Virginia 23284-2000, USA.
    Jena, P.
    Physics Department, Virginia Commonwealth University, Richmond, Virginia 23284-2000, USA.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Effect of Ti and metal vacancies on the electronic structure, stability, and dehydrogenation of Na3AlH6: Supercell band-structure formalism and gradient-corrected density-functional theory2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 73, no 21, article id 214107Article in journal (Refereed)
    Abstract [en]

    Electronic and structural properties of sodium-aluminum hexahydride (Na3AlH6) formed during the decomposition reaction of sodium alanate (NaAlH4) and the effects of Ti catalyst are studied using supercell approach and density-functional theory. The preferred site of Ti has been determined by substituting it at both the Na and Al sites and comparing the respective formation energies. The least unfavorable site for Ti is found to be the Al site. To examine the role of Ti substitution on the desorption of hydrogen, the energy cost to remove a H atom from the vicinity of Ti was calculated and compared with that from the pure Na3AlH6 The improvement in dehydrogenation of Na3AlH6 was found to be due to the weakening the Al-H bond caused by Ti substitution. We also studied the role of metal vacancies on hydrogen desorption. Although this desorption was exothermic, the energies to create these vacancies are high.

  • 280. Li, Sa
    et al.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Araújo, C. Moysés
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Jena, Puru
    Dehydrogenation associated with Ti catalyst in sodium alanate2010In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 71, no 8, p. 1073-1076Article in journal (Refereed)
    Abstract [en]

    Addition of small amount of Ti precursors to sodium alanate has recently been found to substantially improve the kinetics and thermodynamics of hydrogen sorption in sodium alanate. In spite of several attempts, a fundamental understanding of how the catalyst works has remained unattainable. Using first principles methods we have investigated the mechanisms for hydrogen desorption in this material. We conclude that Ti substituted at Al site is energetically most favorable. The small amount of Ti substitution does not introduce large lattice distortion. The Ti atom serves as a magnet that continues to attract nearby H atoms as the nearest ones are successively desorbed. The number of Al atoms near to the Ti site remains at four upon hydrogen desorption when Ti is substituted at the Al site. These results provide important new insight into the design of future catalysts for hydrogen storage materials.

  • 281.
    Li, Sa
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ahuja, Rajeev
    Johansson, B.
    High pressure theoretical studies of actinide dioxides2002In: High Pressure Research, Vol. 22, no 2, p. 471-Article in journal (Refereed)
  • 282.
    Li, Sa
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Jena, Puru
    Araújo, C. Moysés
    Ahuja, Rajeev
    Electronic structure and hydrogen desorption in NaAlH42005In: Mater. Res. Soc. Symp. Proc. (MRS), Vol. 837, no N2.5.1Article in journal (Refereed)
  • 283. Li, Wen
    et al.
    Miao, Ling
    Scheicher, Ralph H.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Xiong, Zhitao
    Wu, Guotao
    Araújo, C. Moysés
    Blomqvist, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Feng, Yuanping
    Chen, Ping
    Li-Na ternary amidoborane for hydrogen storage: experimental and first-principles study2012In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 41, no 16, p. 4754-4764Article in journal (Refereed)
    Abstract [en]

    Li-Na ternary amidoborane, Na[Li(NH2BH3)(2)], was recently synthesized by reacting LiH and NaH with NH3BH3. This mixed-cation amidoborane shows improved dehydrogenation performance compared to that of single-cation amidoboranes, i.e., LiNH2BH3 and NaNH2BH3. In this paper, we synthesized the Li-Na ternary amidoborane by blending and re-crystallizing equivalent LiNH2BH3 and NaNH2BH3 in tetrahydrofuran (THF), and employed first-principles calculations and the special quasirandom structure (SQS) method to theoretically explore the likelihood for the existence of Li1-xNax(NH2BH3) for various Li/Na ratios. The thermodynamic, electronic and phononic properties were investigated to understand the possible dehydrogenation mechanisms of Na[Li(NH2BH3)(2)].

  • 284. Li, Wen
    et al.
    Scheicher, Ralph H.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Araujo, C. Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Wu, Guotao
    Blomqvist, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Wu, Chenzhang
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Feng, Yuan Ping
    Chen, Ping
    Understanding from First-Principles Why LiNH2BH3 · NH3BH3 Shows Improved Dehydrogenation over LiNH2BH3 and NH3BH32010In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, no 44, p. 19089-19095Article in journal (Refereed)
    Abstract [en]

    Lithium amidoborane-ammonia borane (LiNH2BH3 center dot NH3BH3, LiAB center dot AB for short) was synthesized recently. Compared with lithium amidoborane (LiNH2BH3, LiAB for short) and ammonia borane (NH3BH3, AB for short), this new ammonia borane derivative has better dehydrogenation kinetics and releases 14.8 wt % hydrogen with peak temperatures at ca. 80 and 140 degrees C, respectively. In this report, first-principles calculations were employed to reveal the differences in dehydrogenation properties of AB, LiAB, and LiAB center dot AB. Furthermore, we attempted to correlate the crystal structure and electronic properties with dehydrogenation performance. The results show that Li+ cations play similar roles in LiAB center dot AB as in LiAB in destabilizing the B-H and N-H bonds, and the mechanism of the first-step dehydrogenation of LiAB center dot AB is likely via the dissociation and combination of hydridic H delta-(B) from LiAB molecule and protonic H delta+(N) from the adjacent AB molecule, rather than from the [LiAB] or [AB] layer alone, resulting in the desorption of H-2 at lower temperatures.

  • 285. Li, Wen
    et al.
    Wu, Guotao
    Araujo, Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Scheicher, Ralph H
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Blomqvist, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Xiong, Zhitao
    Feng, Yuanping
    Chen, Ping
    Li+ ion conductivity and diffusion mechanism in α-Li3N and β-Li3N2010In: Energy & environmental science, ISSN 1754-5692, Vol. 3, no 10, p. 1524-1530Article in journal (Refereed)
    Abstract [en]

    beta-Li3N of hexagonal D-6h(4) (P6(3)/mmc) structure was synthesized by   high-energy ball milling commercial Li3N (composed of both alpha and   beta phases). Ionic conductivities of alpha-Li3N and beta-Li3N were   tested by direct current (D. C.) and alternating current (A. C.)   impedance methods. beta-Li3N exhibited the same order of magnitude of   Li+ ion conductivity (2.085 x 10(-4) S cm(-1)) as that of alpha-Li3N   (5.767 x 10(-4) S cm(-1)) at room temperature. First-principles   calculations were employed to simulate the diffusion mechanism of Li+   ion in alpha-Li3N and beta-Li3N. Our results indicate that the   diffusion of Li+ ion in beta-Li3N likely occurs between pure Li-beta(1)   planes, which is different from that in alpha-Li3N, where the diffusion   of Li+ ion occurs within Li2N plane. The Li+ ion migration energy  barriers (E-m) for alpha-Li3N and beta-Li3N are 0.007 eV and 0.038 eV, respectively.

  • 286. Li, Yan-Ling
    et al.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Lin, Hai-Qing
    Structural phase transition and metallization in compressed SrC22014In: Chinese Science Bulletin, ISSN 1001-6538, E-ISSN 1861-9541, Vol. 59, no 36, p. 5269-5271Article in journal (Refereed)
    Abstract [en]

    The structural, dynamical, and electronic properties of compressed SrC2 were systematically investigated up to 200 GPa by using ab initio method. Three new phases are obtained by means of evolutionary algorithm. The confirmed most stable structure has C2/c symmetry at zero pressure, which transforms into an orthorhombic Cmcm phase at 4.5 GPa, followed by another orthorhombic Immm phase, which is stabilized at wide pressure range of 21.5-123.5 GPa, and then transformed into MgB2-type phase (space group, P6/mmm). Although SrC2 has similar structural transformation to that of compressed CaC2, SrC2 holds small electron-phonon coupling, which leads to its low superconducting critical temperature (only 1.8 K).

  • 287.
    Li, Yan-Ling
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Chen, Xiao-Jia
    Zeng, Zhi
    Lin, Hai-Qing
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Formation of Nanofoam carbon and re-emergence of Superconductivity in compressed CaC62013In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 3, p. 3331-Article in journal (Refereed)
    Abstract [en]

    Pressure can tune material's electronic properties and control its quantum state, making some systems present disconnected superconducting region as observed in iron chalcogenides and heavy fermion CeCu2Si2. For CaC6 superconductor (T-c of 11.5 K), applying pressure firstTc increases and then suppresses and the superconductivity of this compound is eventually disappeared at about 18 GPa. Here, we report a theoretical finding of the re-emergence of superconductivity in heavily compressed CaC6. The predicted phase III (space group Pmmn) with formation of carbon nanofoam is found to be stable at wide pressure range with a Tc up to 14.7 K at 78 GPa. Diamond-like carbon structure is adhered to the phase IV (Cmcm) for compressed CaC6 after 126 GPa, which has bad metallic behavior, indicating again departure from superconductivity. Re-emerged superconductivity in compressed CaC6 paves a new way to design new-type superconductor by inserting metal into nanoporous host lattice.

  • 288.
    Li, Yan-Ling
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Zeng, Zhi
    Lin, Hai-Qing
    Mao, Ho-Kwang
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pressure-induced superconductivity in CaC22013In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 110, no 23, p. 9289-9294Article in journal (Refereed)
    Abstract [en]

    Carbon can exist as isolated dumbbell, 1D chain, 2D plane, and 3D network in carbon solids or carbon-based compounds, which attributes to its rich chemical binding way, including sp-, sp2-, and sp3-hybridized bonds. sp2-hybridizing carbon always captures special attention due to its unique physical and chemical property. Here, using an evolutionary algorithm in conjunction with ab initio method, we found that, under compression, dumbbell carbon in CaC2 can be polymerized first into 1D chain and then into ribbon and further into 2D graphite sheet at higher pressure. The C2/m structure transforms into an orthorhombicCmcm phase at 0.5 GPa, followed by another orthorhombic Immm phase, which is stabilized in a wide pressure range of 15.2–105.8 GPa and then forced into MgB2-type phase with wide range stability up to at least 1 TPa. Strong electron–phonon coupling λ in compressed CaC2 is found, in particular for Immmphase, which has the highest λ value (0.562–0.564) among them, leading to its high superconducting critical temperature Tc (7.9∼9.8 K), which is comparable with the 11.5 K value of CaC6. Our results show that calcium not only can stabilize carbon sp2 hybridization at a larger range of pressure but also can contribute in superconducting behavior, which would further ignite experimental and theoretical interest in alkaline–earth metal carbides to uncover their peculiar physical properties under extreme conditions.

  • 289.
    Li, Yunguo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Larsson, J. Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Communication: Origin of the difference between carbon nanotube armchair and zigzag ends2014In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 140, no 9, p. 091102-Article in journal (Refereed)
    Abstract [en]

    In this work, we have found that the difference between armchair and zigzag ends of carbon nanotubes (CNTs) does not pertain at close study for individual bonds and thus alternative strategies need to be developed to reach the ultimate goals in selective growth. Based on first-principles simulations, the difference between binding strengths for CNTs of different chirality was investigated using hydrogen dissociation energies at their passivated ends. When all H atoms are removed collectively we find the well-known difference: that armchair bonds are much weaker than zigzag ones, which is typically seen for both CNT ends and graphene edges. However, when individual H atoms are removed we find almost no difference in hydrogen dissociation energies, small difference in bond lengths, which by association means small difference in C-C and M-C binding energies. We show convincingly that the difference in binding energy between armchair and zigzag ends is due to a fragment stabilization effect that is only manifested when all (or several neighbouring) bonds are broken. This is because at armchair ends/edges neighbouring dangling bonds can pair-up to form C C triple bonds that constitute a considerable stabilization effect compared to the isolated dangling bonds at zigzag ends/edges. Consequently, in many processes, e. g., catalytic growth where bonds are normally created/broken sequentially, not collectively, the difference between armchair and zigzag ends/edges cannot be used to discriminate growth of one type over the other to achieve chiral selective growth. Strategies are discussed to realize chirality selective growth in the light of the results presented, including addition of C-2-fragments to favor armchair tubes. (C) 2014 AIP Publishing LLC.

  • 290. Li, Yunguo
    et al.
    De Sarkar, Abir
    Pathak, Biswarup
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Strain-induced stabilization of Al functionalization in graphene oxide nanosheet for enhanced NH3 storage2013In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 102, no 24, p. 243905-Article in journal (Refereed)
    Abstract [en]

    Strain effects on the stabilization of Al ad-atom on graphene oxide (GO) nanosheet as well as its implications for NH3 storage have been investigated using first-principles calculations. Tensile strain is found to be very effective in stabilizing the Al ad-atom on GO. It strengthens the C-O bonds through an enhanced charge transfer from C to O atoms. Interestingly, Al's stability is governed by the bond strength of C-O rather than that of Al-O. Optimally strained Al-functionalized GO binds up to 6 NH3 molecules, while it binds no NH3 molecule in unstrained condition.

  • 291.
    Li, Yunguo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hussain, Tanveer
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sarkar, Abir De
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hydrogen storage in polylithiated BC3 monolayer sheet2013In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 170, p. 39-43Article in journal (Refereed)
    Abstract [en]

    We perform a detailed study on the stability, electronic structure and hydrogen storage capacity of polylithiated (CLi3 functionalized) boron carbide (BC3) monolayer sheet using first-principles calculations. The binding of the CLi3 radical to the boron carbide (BC3) monolayer sheet is found to be large enough to ensure its uniform distribution without any clustering. The structural stability has been confirmed by molecular dynamics. Each lithium atom is able to accommodate 4 H2 molecules with an average binding energy of 0.21 eV, which is suitable for reversible H2 adsorption/desorption at ambient temperatures. The uptake of H2 is found to reach up to 9.83 wt% in polylithiated BC3 monolayer sheet.

  • 292.
    Li, Yunguo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Li, Yan-Ling
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Single-layer MoS2 as an efficient photocatalyst2013In: Catalysis Science & Technology, ISSN 2044-4753, Vol. 3, no 9, p. 2214-2220Article in journal (Refereed)
    Abstract [en]

    The potential application of the single-layer MoS2 as a photocatalyst was revealed based on first-principles calculations. It is found that the pristine single-layer MoS2 is a good candidate for hydrogen production, and its catalysing ability can be tuned by the applied mechanical strain. Furthermore, the p-type doping could make the single layer a good photocatalyst for the overall water splitting.

  • 293.
    Li, Yunguo
    et al.
    Jiangsu Normal Univ, Sch Phys & Elect Engn, Xuzhou, Peoples R China.;UCL, Dept Earth Sci, Crystallog & Mineral Phys, Gower St, London WC1E 6BT, England..
    Li, Yan-Ling
    Jiangsu Normal Univ, Sch Phys & Elect Engn, Xuzhou, Peoples R China..
    Sa, Baisheng
    Fuzhou Univ, Coll Mat Sci & Engn, Fuzhou, Peoples R China..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Review of two-dimensional materials for photocatalytic water splitting from a theoretical perspective2017In: Catalysis Science & Technology, ISSN 2044-4753, E-ISSN 2044-4761, Vol. 7, no 3, p. 545-559Article, review/survey (Refereed)
    Abstract [en]

    Two-dimensional (2D) materials have shown extraordinary performances as photocatalysts compared to their bulk counterparts. Simulations have made a great contribution to the deep understanding and design of novel 2D photocatalysts. Ab initio simulations based on density functional theory (DFT) not only show efficiency and reliability in new structure searching, but also can provide a reliable, efficient, and economic way for screening the photocatalytic property space. In this review, we summarize the recent developments in the field of water splitting using 2D materials from a theoretical perspective. We address that DFT-based simulations can fast screen the potential spaces of photocatalytic properties with the accuracy comparable to experiments, by investigating the effects of various physical/ chemical perturbations. This, at last, will lead to the enhanced photocatalytic activities of 2D materials, and promote the development of photocatalysis.

  • 294.
    Li, Yunguo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Li, Yan-Ling
    Sun, Weiwei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Dynamic stability of the single-layer transition metal dichalcogenides2014In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 92, p. 206-212Article in journal (Refereed)
    Abstract [en]

    In the quest for advanced semi-conductors, we have expanded our knowledge on a series of single-layer TMDs by calculating the electronic structure and lattice dynamic stability based on the first-principles density functional theory. The single layers of Mo and W dichalcogenides are found to be stable with P-6m2 symmetry. The reduction of dimension opens up and increases the bandgap. The charge transfer is found to decrease from sulfide to selenide and to telluride due to the decrease of electronegativity of chalcogen, which also induces the reduction of bandgap. The TA mode softening is found along Gamma-K direction and becomes more significant from sulfide to selenide and to telluride in the single-layer TMDs of Mo and W, which corresponds to the vibration of transition metal cations along y-axis. The single layers of Nb dichalcogenides are found to be instable with P-6m2 symmetry but stable with P-3m1 symmetry. It is also speculated that the interactions of cations mediated by electron-phonon coupling are accountable for the dynamic instability of the single-layer TMDs of Nb with P-6m2 symmetry. The unstable P-6m2 single-layer Nb dichalcogenides can transform to the stable P-3m1 structure during the exfoliation from the bulk, via the displacement of two anion layers of the sandwich structure.

  • 295.
    Li, Yunguo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pathak, Biswarup
    Nisar, Jawad
    Qian, Zhao
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Metal-decorated graphene oxide for ammonia adsorption2013In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 103, no 2, p. 28007-Article in journal (Refereed)
    Abstract [en]

    Based on the first-principles density functional theory, we have studied the stability, electronic structure and ammonia storage capacity of metal-decorated graphene oxide (GO). Metal atoms (Mg and Li) are bonded strongly to the epoxy oxygen atoms on the surface of the GO sheet, which can act as high-surface-area adsorbent for the ammonia uptake and release. Each metal atom can bind several ammonia molecules around itself with a reasonable binding energy. We find metal-decorated GO can store up to tens of moles of ammonia per kilogram, which is far better than the recently reported excellent ammonia adsorption by GO.

  • 296. Liao, Jiamin
    et al.
    Sa, Baisheng
    Zhou, Jian
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sun, Zhimei
    Design of High-Efficiency Visible-Light Photocatalysts for Water Splitting: MoS2/AlN(GaN) Heterostructures2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 31, p. 17594-17599Article in journal (Refereed)
    Abstract [en]

    Hydrogen fuel produced from water splitting using solar energy and a catalyst is a clean and renewable future energy source. Great efforts in searching for photocatalysts that are highly efficient, inexpensive, and capable of harvesting sunlight have been made for the last decade, which, however, have not yet been achieved in a single material system so far. Here, we predict that MoS2/AlN(GaN) van der Waals (vdW) heterostructures are sufficiently efficient photocatalysts for water splitting under visible-light irradiation based on ab initio calculations. Contrary to other investigated photocatalysts, MoS2/AlN(GaN) vdW heterostructures can separately produce hydrogen and oxygen at the opposite surfaces, where the photoexcited electrons transfer from AlN(GaN) to MoS2 during the photocatalysis process. Meanwhile, these vdW heterostructures exhibit significantly improved photocatalytic properties under visible-light irradiation by the calculated optical absorption spectra. Our findings pave a new way to facilitate the design of photocatalysts for water splitting.

  • 297.
    Liu, Peng
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    De Sarkar, Abir
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Shear strain induced indirect to direct transition in band gap in AlN monolayer nanosheet2014In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 86, p. 206-210Article in journal (Refereed)
    Abstract [en]

    The electronic band structure of aluminum nitride (AlN) nanosheets under different kinds of strains has been investigated. Our first principles based studies show that the homogeneous biaxial strain is most effective as compared to uniaxial and shear strain in tuning the band gap. Large shear strain (>= 7.5%) and 10% uniaxial strain along the zig-zag direction induces an indirect-to-direct transition in band gap. The response of these 2 dimensional AlN nanosheets to strain is different from that of its 3 dimensional bulk phase counterparts to pressure. Quantum confinement effects govern the behavior of the former. The dynamical stability of AlN nanosheets have also been assessed under different modes of strains through phonon dispersion calculations. The AlN nanosheets are found to be dynamically stable under tensile strain and shear strain along zig-zag directions, while the sheets are found to be unstable under compressive strain.

  • 298.
    Liu, Peng
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Nisar, Jawad
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pathak, Biswarup
    Layered Perovskite Sr2Ta2O7 for Visible Light Photocatalysis: A First Principles Study2013In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 10, p. 5043-5050Article in journal (Refereed)
    Abstract [en]

    The layered perovskite Sr2Ta2O7 has been investigated for efficient visible light photocatalysis using the first principles study. The electronic structure of Sr2Ta2O7 is tuned by the anionic (N)/cationic (Mo, W) mono- and co-doping. Such doping creates impurity states in the band gap and therefore reduces the band gap significantly. The absolute band edge position of the doped Sr2Ta2O7 with respect to the water oxidation/reduction potential depends a lot on the p/d-orbital's energies of anionic/cationic dopants, respectively. The stability of the co-doped system is governed by the Coulomb interactions and charge compensation effects.

  • 299. Liu, Peng
    et al.
    Nisar, Jawad
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pathak, Biswarup
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Cationic-anionic mediated charge compensation on La2Ti2O7 for visible light photocatalysis2013In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, no 40, p. 17150-17157Article in journal (Refereed)
    Abstract [en]

    The cationic-anionic mediated charge compensation effect was studied in the layered perovskite La2Ti2O7 for the visible light photocatalysis. Our screened hybrid density functional study shows that the electronic structure of La2Ti2O7 can be tuned by the cationic (V, Nb, Ta)/anionic (N) mono-and co-doping. Such mono-doping creates impurity states in the band gap which helps the electron-hole recombination. But if the charge compensation is made by the cationic-anionic mediated co-doping then such impurity states can be removed and can be a promising strategy for visible light photocatalysis. The absolute band edge position of the doped La2Ti2O7 has been aligned with respect to the water oxidation/reduction potential. The calculated defect formation energy shows the stability of the co-doping system is improved due to the coulomb interactions and charge compensations effect.

  • 300.
    Liu, Peng
    et al.
    Department of Materials and Engineering, The Royal Institute of Technology (KTH).
    Nisar, Jawad
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pathak, Biswarup
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hybrid density functional study on SrTiO3 for visible light photocatalysis2012In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 37, no 16, p. 11611-11617Article in journal (Refereed)
    Abstract [en]

    Hybrid Density Functional calculations have been performed on the electronic structure of anionic mono- (S, N, P, and C) and co-doped (N-N, N-P, N-S, P-P) SrTiO3 to improve their visible light photocatalytic activity. The electronic band position of doped system has been aligned with respect to the water oxidation/reduction potential. The electronic band position and optical absorption study shows that the mono- (S) and co-doped (N-N, N-P and P-P) SrTiO3 systems are promising materials for the visible-light photocatalysis. The calculated binding energies show that the co-doped systems are more stable than their respective mono-doped systems.

3456789 251 - 300 of 551
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf