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  • 101.
    Cricchio, F
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Ahuja, Rajeev
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    High Pressure melting of Lead2006In: Phys. Rev. B, Vol. 73, p. 140103-Article in journal (Refereed)
  • 102.
    Dahlstrand, Christian
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Jahn, Burkhard O.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Grigoriev, Anton
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Villaume, Sebastien
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Polyfulvenes: Polymers with "Handles" That Enable Extensive Electronic Structure Tuning2015In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 46, p. 25726-25737Article in journal (Refereed)
    Abstract [en]

    The fundamental electronic structure properties of substituted poly(penta)fulvenes and pentafulvene-based polymers are analyzed through qualitative molecular orbital (MO) theory combined with calculations at the B3LYP and HSE06 hybrid density functional theory (DFT) levels. We argue that the pentafulvene monomer unit has a unique character because electron density in the exocyclic C=C double bond can be polarized into and out of the five-membered ring, a feature that is not available to other more commonly used monomers. It is investigated how the energy gaps between the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO, respectively), as approximate band gaps, are influenced by exocyclic substitution, introduction of linker groups, benzannulation, and ring substitution. In particular, the exocyclic positions of the fulvene act as handles by which the electronic structure of the polymer can be tuned between the quinoid and fulvenoid valence bond isomers; electron-withdrawing exocyclic substituents lead to polyfulvenes in the quinoid form while those with electron-donating substituents prefer the fulvenoid. Taken together, the HOMO-LUMO gaps of polyfulvenes can be tuned extensively, varying in ranges 0.77-2.44 eV (B3LYP) and 0.35-2.00 eV (HSE06) suggesting that they are a class of polymers with highly interesting, yet nearly unexplored, properties.

  • 103. Dallera, C.
    et al.
    Wessely, Ola
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Colarieti-Tosti, M.
    Eriksson, Olle
    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.
    Katsnelson, M. I.
    Annese, E.
    Rueff, J.-P.
    Vank'o, G.
    Braicovich, L.
    Grioni, M.
    Understanding mixed valent materials: Effects of dynamical core-hole screening in high-pressure x-ray spectroscopy2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, no 8, p. 081101-Article in journal (Refereed)
    Abstract [en]

    Changes in the electronic structure of Yb, a material whose valence is modified under pressure, are observed with remarkable detail in x-ray absorption and emission data measured between ambient conditions and 20 GPa. These changes are reproduced by a theory that essentially does not rely on experimental parameters, and includes dynamical core-hole screening. From the combined experimental and theoretical data we can firmly establish on a quantitative level how the valency of an intermediate valence material is modified by pressure. In metallic Yb it increases from 2 to 2.55 +/- 0.05 between 0 and 20 GPa.

  • 104.
    Das, Suman
    et al.
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India..
    Swain, Diptikanta
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India..
    Araujo, Rafael Barros Neves de
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Shi, Songxin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Beihang Univ, Sch Mat Sci & Engn, Beijing 100191, Peoples R China..
    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, S-10044 Stockholm, Sweden..
    Row, Tayur N. Guru
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India..
    Bhattacharyya, Aninda J.
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India..
    Alloying in an Intercalation Host: Metal Titanium Niobates as Anodes for Rechargeable Alkali-Ion Batteries2018In: Chemistry - An Asian Journal, ISSN 1861-4728, E-ISSN 1861-471X, Vol. 13, no 3, p. 299-310Article in journal (Refereed)
    Abstract [en]

    We discuss here a unique flexible non-carbonaceous layered host, namely, metal titanium niobates (M-Ti-niobate, M: Al3+, Pb2+, Sb3+, Ba2+, Mg2+), which can synergistically store both lithium ions and sodium ions via a simultaneous intercalation and alloying mechanisms. M-Ti-niobate is formed by ion exchange of the K+ ions, which are specifically located inside galleries between the layers formed by edge and corner sharing TiO6 and NbO6 octahedral units in the sol-gel synthesized potassium titanium niobate (KTiNbO5). Drastic volume changes (approximately 300-400%) typically associated with an alloying mechanism of storage are completely tackled chemically by the unique chemical composition and structure of the M-Ti-niobates. The free space between the adjustable Ti/Nb octahedral layers easily accommodates the volume changes. Due to the presence of an optimum amount of multivalent alloying metal ions (50-75% of total K+) in the M-Ti-niobate, an efficient alloying reaction takes place directly with ions and completely eliminates any form of mechanical degradation of the electroactive particles. The M-Ti-niobate can be cycled over a wide voltage range (as low as 0.01V) and displays remarkably stable Li+ and Na+ ion cyclability (>2 Li+/Na+ per formula unit) for widely varying current densities over few hundreds to thousands of successive cycles. The simultaneous intercalation and alloying storage mechanisms is also studied within the density functional theory (DFT) framework. DFT expectedly shows a very small variation in the volume of Al-titanium niobate following lithium alloying. Moreover, the theoretical investigations also conclusively support the occurrence of the alloying process of Li ions with the Al ions along with the intercalation process during discharge. The M-Ti-niobates studied here demonstrate a paradigm shift in chemical design of electrodes and will pave the way for the development of a multitude of improved electrodes for different battery chemistries.

  • 105.
    de Almeida, J. S.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Kim, D. Y.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Ortiz, C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Klintenberg, Mattias
    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.
    On the dynamical stability and metallic behavior of YH3 under pressure2009In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 94, no 25, p. 251913-Article in journal (Refereed)
    Abstract [en]

    Wereport on the behavior of structural and electronic properties ofyttrium trihydride under pressure using first principles calculations. We showthat YH3 undergoes a structural transformation and its high pressurephase is dynamically stable under pressure since the peak atthe imaginary frequencies of the phonon density of states, whichaccount for the structural instability disappears at high pressure. Additionally,our GW calculations indicate a metallization of the high pressurecubic phase of YH3.

  • 106. De Sarkar, Abir
    et al.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Electronic charge transport through ZnO nanoribbons2014In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 75, no 11, p. 1223-1228Article in journal (Refereed)
    Abstract [en]

    I-V characteristics of ZnO nanoribbons (NRs) have been investigated using density functional theory coupled to non-equilibrium Green's Function. The current through the NRs drops with the increasing NR width, leveling off to 1.66 and 0.42 mu A in zig-zag and arm-chair NRs respectively for widths similar to 20 angstrom at 3 V of electrical bias. The transconductance as well as the current flowing through the arm-chair NRs decays exponentially with NR width for both odd and even number of dimer lines traversed. The current through the zig-zag NRs falls off exponentially with NR width, being insensitive to the odd or even numbers of zig-zag lines appearing along the normal to the charge transport direction.

  • 107. Dera, Przemyslaw
    et al.
    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.
    Tkachev, Sergey
    Prakapenka, Vitali B.
    New type of possible high-pressure polymorphism in NiAs minerals in planetary cores2013In: Physics and chemistry of minerals, ISSN 0342-1791, E-ISSN 1432-2021, Vol. 40, no 2, p. 183-193Article in journal (Refereed)
    Abstract [en]

    The nickel arsenide (B8(1)) and related crystal structures are among the most important crystallographic arrangements assumed by Fe and Ni compounds with light elements such as Si, O, S, and P, expected to be present in planetary cores. Despite the simple structure, some of these materials like troilite (FeS) exhibit complex phase diagrams and rich polymorphism, involving significant changes in interatomic bonding and physical properties. NiP (oP16) represents one of the two principal structure distortions found in the nickel arsenide family and is characterized by P-P bonding interactions that lead to the formation of P-2 dimers. In the current study, the single-crystal synchrotron X-ray diffraction technique, aided by first principles density functional theory (DFT) calculations, has been applied to examine the compression behavior of NiP up to 30 GPa. Two new reversible displacive phase transitions leading to orthorhombic high-pressure phases with Pearson symbols oP40 and oC24 were found to occur at approximately 8.5 and 25.0 GPa, respectively. The oP40 phase has the primitive Pnma space group with unit cell a = 4.7729(5) , b = 16.6619(12) , and c = 5.8071(8) at 16.3(1) GPa and is a superstructure of the ambient oP16 phase with multiplicity of 2.5. The oC24 phase has the acentric Cmc2(1) space group with unit cell a = 9.695(6) , b = 5.7101(9) , and c = 4.7438(6) at 28.5(1) GPa and is a superstructure of the oP16 phase with multiplicity of 1.5. DFT calculations fully support the observed sequence of phase transitions. The two new phases constitute logical next stages of P sublattice polymerization, in which the dilution of the P-3 units, introduced in the first high-pressure phase, decreases, leading to compositions of Ni-20(P-3)(4)(P-2)(4) and Ni-12(P-3)(4), and provide important clues to understanding of phase relations and transformation pathways in the NiAs family.

  • 108. Deshpande, M D
    et al.
    Scheicher, Ralph H
    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.
    Pandey, Ravindra
    Binding strength of sodium ions in cellulose for different water contents2008In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 112, no 30, p. 8985-8989Article in journal (Refereed)
    Abstract [en]

    The interaction strength of sodium ions (Na(+)) with cellulose is investigated from first principles for varying degrees of water content. We find that the interaction of water molecules and Na(+) can be studied independently at the various OH groups in cellulose which we categorize as two different types. In the absence of water, Na(+) forms strong ionic bonds with the OH groups of cellulose. When water molecules are anchored to the OH groups via hydrogen bonds, Na(+) can eventually no longer bind to the OH groups, but will instead interact with the oxygen atoms of the water molecules. Due to the rather weak attachment of the latter to the OH groups, Na(+) becomes effectively more mobile in the fully hydrated cellulose framework. The present study thus represents a significant step toward a first-principles understanding of the experimentally observed dependence of ionic conductivity on the level of hydration in cellulose network.

  • 109.
    Ding, Feng
    et al.
    Fysiska Institutionen, Göteborgs Universitet.
    Larsson, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Larsson, J Andreas
    Tyndall National Institute, Unversity College Cork.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Duan, Haiming
    Fysiska Institutionen, Göteborgs Universitet.
    Rosén, Arne
    Fysiska Institutionen, Göteborgs Universitet.
    Bolton, Kim
    University College of Borås.
    The importance of strong carbon-metal adhesion for catalytic nucleation of single-walled carbon nanotubes2008In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 8, no 2, p. 463-468Article in journal (Refereed)
    Abstract [en]

    Density functional theory is used to show that the adhesion between single-walled carbon nanotubes (SWNTs) and the catalyst particles from which they grow needs to be strong to support nanotube growth. It is found that Fe, Co, and Ni, commonly used to catalyze SWNT growth, have larger adhesion strengths to SWNTs than Cu, Pd, and Au and are therefore likely to be more efficient for supporting growth. The calculations also show that to maintain an open end of the SWNT it is necessary that the SWNT adhesion strength to the metal particle is comparable to the cap formation energy of the SWNT end. This implies that the difference between continued and discontinued SWNT growth to a large extent depends on the carbon-metal binding strength, which we demonstrate by molecular dynamics (MD) simulations. The results highlight that first principles computations are vital for the understanding of the binding strength's role in the SWNT growth mechanism and are needed to get accurate force field parameters for MD.

  • 110. Ding, Yang
    et al.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Shu, Jinfu
    Chow, Paul
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Mao, Ho-kwang
    Structural phase transition of vanadium at 69 GPa2007In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 98, no 8, p. 085502-Article in journal (Refereed)
    Abstract [en]

    A phase transition was observed at 63-69 GPa and room temperature in vanadium with synchrotron x-ray diffraction. The transition is characterized as a rhombohedral lattice distortion of the body-centered-cubic vanadium without a discontinuity in the pressure-volume data, thus representing a novel type of transition that has never been observed in elements. Instead of driven by the conventional s-d electronic transition mechanism, the phase transition could be associated with the softening of C-44 trigonal elasticity tensor that originates from the combination of Fermi surface nesting, band Jahn-Teller distortion, and electronic topological transition.

  • 111. Dixit, M.
    et al.
    Maark, Tuhina Adit
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ghatak, K.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pal, S.
    Scandium-decorated MOF-5 as potential candidates for room-temperature hydrogen storage: A solution for the clustering problem in MOFs2012In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, no 33, p. 17336-17342Article in journal (Refereed)
    Abstract [en]

    Transition-metal-based systems show promising binding energy for hydrogen storage but suffer from clustering problem. The effect of light transition metal (M = Sc, Ti) decoration, boron substitution on the hydrogen storage properties of MOF-5, and clustering problem of metals has been investigated using ab initio density functional theory. Our results of solid-tate calculations reveal that whereas Ti clusters strongly Sc atoms do not suffer from this problem when decorating MOF-5. Boron substitution on metal-decorated MOF-5 enhances the interaction energy of both the metals with MOF-5. Sc-decorated MOF-5 shows a hydrogen storage capacity of 5.81 wt % with calculated binding energies of 20-40 kJ/mol, which ensures the room-temperature applicability of this hydrogen storage material.

  • 112.
    Djouambi, Nadia
    et al.
    Univ Badji Mokhtar Annaba, Lab Mat Avances, BP 12, El Hadjar 23000, Annaba, Algeria.
    Bougheloum, Chafika
    Univ Badji Mokhtar Annaba, Lab Mat Avances, BP 12, El Hadjar 23000, Annaba, Algeria.
    Messalhi, Abdelrani
    Univ Badji Mokhtar Annaba, Lab Mat Avances, BP 12, El Hadjar 23000, Annaba, Algeria.
    Bououdina, Mohamed
    Univ Bahrain, Coll Sci, Dept Phys, POB 32038, Zallaq, Bahrain.
    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. Royal Inst Technol KTH, Dept Mat & Engn, Appl Mat Phys, S-10044 Stockholm, Sweden.
    New Concept on Photocatalytic Degradation of Thiophene Derivatives: Experimental and DFT Studies2018In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 27, p. 15646-15651Article in journal (Refereed)
    Abstract [en]

    In this study, the photocatalytic degradation of seven sulfur compounds (2-methylthiophene, 3-methylthiophene, 2-phenylthiophene, 3-phenylthiophene, 2,5-diphenylthiophene, 2-(2-thienyl) pyridine, and 2-(3-thienyl) pyridine in semiaqueous medium are compared to thiophene. The apparent-reaction-rate constant (k) is found to decrease in the following order: 2,5-diphenylthiophene > 2-(2-thienyl) pyridine > 2-penhylthiophene methylthiophene > 3-penhylthiophene > 2-methylthiophene > 2-(3-thienyl) pyridine > 3-thiophene. From the data obtained by UV light absorption (lambda(max)) measurements and electronic structure calculations (frontier orbitals energy, global hardness, and global softness), the kinetic parameters of the reaction have been determined. Among the studied compounds, thiophene with a high lambda(max) and low calculated LUMO-HOMO gap energy has showed higher activity under UV irradiation. Interestingly, a lower activity is observed with low lambda(max) and high LUMO-HOMO gap energy. This demonstrates, for the first time, that the reactivity depends essentially on the thermodynamic stability of the sulfur compound rather than on the nature or the position of the substituent on the ring.

  • 113. Dubrovinskaia, N.
    et al.
    Dubrovinsky, L.
    Kantor, I.
    Crichton, W. A.
    Dmitriev, V.
    Prakapenka, V.
    Shen, G.
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. 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. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Abrikosov, I. A.
    Beating the miscibility barrier between iron and magnesium by high-pressure alloying2005In: Physical Review Letters, Vol. 95, p. 245502-Article in journal (Refereed)
  • 114. Dubrovinsky, L.
    et al.
    Dubrovinskaia, N.
    Crichton, W. A.
    Mikhaylushkin, Arkady S.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Simak, S. I.
    Abrikosov, I. A.
    de Almeida, J. Souza
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ahuja, Rajeev B.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Johansson, B.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Noblest of all metals is structurally unstable at high pressure2007In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 98, no 4, p. 045503-Article in journal (Refereed)
    Abstract [en]

    In a series of experiments in externally electrically heated diamond anvil cells we demonstrate that at pressures above similar to 240 GPa gold adopts a hexagonal-close-packed structure. Ab initio calculations predict that at pressures about 250 GPa different stacking sequences of close-packed atomic layers in gold become virtually degenerate in energy, strongly supporting the experimental observations.

  • 115.
    Dubrovinsky, L.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Dubrovinskaia, N.
    S. de Almeida, J.
    Luo, Wei
    Crichton, W. A.
    Johansson, Börje
    Ahuja, Rajeev
    Relativistic Effects Driven Structural Phase Transition in Gold at High PressureIn: NatureArticle in journal (Refereed)
  • 116.
    Dubrovinsky, LS
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences.
    Saxena, SK
    Lazor, P
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences.
    Ahuja, R
    Eriksson, O
    Wills, JM
    Johansson, B
    Physics, Department of Physics.
    Experimental and theoretical identification of a new high-pressure phase of silica1997In: NATURE, ISSN 0028-0836, Vol. 388, no 6640, p. 362-365Article in journal (Refereed)
    Abstract [en]

    Following the discovery of stishovite (the highest-pressure polymorph of silica known from natural samples), many attempts have been made to investigate the possible existence of denser phases of silica at higher pressures. Based on the crystal structures

  • 117. Dwibedi, Debasmita
    et al.
    Araujo, Rafael B.
    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.
    Shanbogh, Pradeep P.
    Sundaram, Nalini G.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Barpanda, Prabeer
    Na2.44Mn1.79(SO4)(3): a new member of the alluaudite family of insertion compounds for sodium ion batteries2015In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 3, no 36, p. 18564-18571Article in journal (Refereed)
    Abstract [en]

    Sodium-ion batteries have been extensively pursued as economic alternatives to lithium-ion batteries. Investigating the polyanion chemistry, alluaudite structured Na2Fe2II(SO4)(3) has been recently discovered as a 3.8 V positive electrode material (Barpanda et al., Nature Commun., 5: 4358, 2014). Registering the highest ever Fe-III/Fe-II redox potential (vs. Na/Na+) and formidable energy density, it has opened up a new polyanion family for sodium batteries. Exploring the alluaudite family, here we report isotypical Na2+2xMn2-xII(SO4)(3) (x = 0.22) as a novel high-voltage cathode material for the first time. Following low-temperature (ca. 350 degrees C) solid-state synthesis, the structure of this new alluaudite compound has been solved adopting a monoclinic framework (s.g. C2/c) showing antiferromagnetic ordering at 3.4 K. Synergising experimental and ab initio DFT investigation, Na2+2xMn2-xII(SO4)(3) has been found to be a potential high-voltage (ca. 4.4 V) cathode material for sodium batteries.

  • 118.
    Dwibedi, Debasmita
    et al.
    Indian Inst Sci, Mat Res Ctr, Faraday Mat Lab, CV Raman Ave, Bangalore 560012, Karnataka, India..
    Gond, Ritambhara
    Indian Inst Sci, Mat Res Ctr, Faraday Mat Lab, CV Raman Ave, Bangalore 560012, Karnataka, India..
    Dayamani, Allumolu
    Indian Inst Sci, Mat Res Ctr, Faraday Mat Lab, CV Raman Ave, Bangalore 560012, Karnataka, India..
    Araujo, Rafael B.
    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.
    Barpanda, Prabeer
    Indian Inst Sci, Mat Res Ctr, Faraday Mat Lab, CV Raman Ave, Bangalore 560012, Karnataka, India..
    Na2.32Co1.84(SO4)(3) as a new member of the alluaudite family of high-voltage sodium battery cathodes2017In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 46, no 1, p. 55-63Article in journal (Refereed)
    Abstract [en]

    Electrochemical energy storage has recently seen tremendous emphasis being placed on the large-scale (power) grid storage. Sodium-ion batteries are capable of achieving this goal with economic viability. In a recent breakthrough in sodium-ion battery research, the alluaudite framework (Na2Fe2(SO4)(3)) has been reported, with the highest Fe3+/Fe2+ redox potential (ca. 3.8 V, Barpanda, et al., Nat. Commun., 2014, 5, 4358). Exploring this high-voltage sodium insertion system, we report the discovery of Na2+2xCo2-x(SO4)(3) (x = 0.16) as a new member of the alluaudite class of cathode. Stabilized by low-temperature solid-state synthesis (T <= 350 degrees C),this novel Co-based compound assumes a monoclinic structure with C2/c symmetry, which undergoes antiferromagnetic ordering below 10.2 K. Isotypical to the Fe-homologue, it forms a complete family of solid-solution Na2+2x(Fe1-yCoy)(2-x)(SO4)(3) [ y = 0-1]. Ab initio DFT analysis hints at potential high voltage operation at 4.76-5.76 V (vs. Na), depending on the degree of desodiation involving a strong participation of the oxygen sub-lattice. With the development of safe organic electrolytes, Na2+2xCo2-x(SO4)(3) can work as a cathode material (similar to 5 V) for sodium-ion batteries.

  • 119.
    Dwibedi, Debasmita
    et al.
    Indian Inst Sci, Mat Res Ctr, Faraday Mat Lab, CV Raman Ave, Bangalore 560012, Karnataka, India..
    Ling, Chris D.
    Univ Sydney, Sch Chem, Bldg F11, Sydney, NSW 2006, Australia..
    Araujo, Rafael B.
    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.
    Duraisamy, Shanmughasundaram
    Indian Inst Sci, Inorgan & Phys Chem, CV Raman Ave, Bangalore 560012, Karnataka, India..
    Munichandraiah, Nookala
    Indian Inst Sci, Inorgan & Phys Chem, CV Raman Ave, Bangalore 560012, Karnataka, India..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Barpanda, Prabeer
    Indian Inst Sci, Mat Res Ctr, Faraday Mat Lab, CV Raman Ave, Bangalore 560012, Karnataka, India..
    Ionothermal Synthesis of High-Voltage Alluaudite Na2+2xFe2-x(SO4)(3) Sodium Insertion Compound: Structural, Electronic, and Magnetic Insights2016In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 8, no 11, p. 6982-6991Article in journal (Refereed)
    Abstract [en]

    Exploring future cathode materials for sodium-ion batteries, alluaudite class of Na2Fe2II(SO4)(3) has been recently unveiled as a 3.8 V positive insertion candidate (Barpanda et al. Nat. Commun. 2014, 5, 4358). It forms an Fe-based polyanionic compound delivering the highest Fe-redox potential along with excellent rate kinetics and reversibility. However, like all known SO4-based insertion materials, its synthesis is cumbersome that warrants careful processing avoiding any aqueous exposure. Here, an alternate low temperature ionothermal synthesis has been described to produce the alluaudite Na2+2xFe2-xII(SO4)(3). It marks the first demonstration of solvothermal synthesis of alluaudite Na2+2xM2-xII(SO4)(3) (M = 3d metals) family of cathodes. Unlike classical solid-state route, this solvothermal route favors sustainable synthesis of homogeneous nanostructured alluaudite products at only 300 degrees C, the lowest temperature value until date. The current work reports the synthetic aspects of pristine and modified ionothermal synthesis of Na2+2xFe2-xII(SO4)(3) having tunable size (300 nm similar to 5 mu m) and morphology. It shows antiferromagnetic ordering below 12 K. A reversible capacity in excess of 80 mAh/g was obtained with good rate kinetics and cycling stability over 50 cycles. Using a synergistic approach combining experimental and ab initio DFT analysis, the structural, magnetic, electronic, and electrochemical properties and the structural limitation to extract full capacity have been described.

  • 120.
    El Hamri, M.
    et al.
    Univ Moulay Ismail, Unite CNRST URAC 08, LP2MS, Phys Dept,Fac Sci, BP 11201, Meknes, Morocco..
    Bouhou, S.
    Univ Moulay Ismail, Unite CNRST URAC 08, LP2MS, Phys Dept,Fac Sci, BP 11201, Meknes, Morocco..
    Essaoudi, I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Univ Moulay Ismail, Unite CNRST URAC 08, LP2MS, Phys Dept,Fac Sci, BP 11201, Meknes, Morocco..
    Ainane, A.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Univ Moulay Ismail, Unite CNRST URAC 08, LP2MS, Phys Dept,Fac Sci, BP 11201, Meknes, Morocco.;Max Planck Inst Phys Complexer Syst, Nothnitzer Str 38, D-01187 Dresden, Germany..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    A theoretical study of the hysteresis behaviors of a transverse spin-1/2 Ising nanocube2016In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 413, p. 30-38Article in journal (Refereed)
    Abstract [en]

    The applied magnetic field dependencies of the surface shell, core and total magnetizations of a transverse spin -I Ising nanocube are investigated within the effective -field theory with correlations, based on the probability distribution technique, for both ferro- and antiferromagnetic exchange interactions. We have found that interfacial coupling has a strong effect on the shape and the number of hysteresis loops and also on the coercive field and remanent magnetization behaviors. Furthermore, when the temperature exceeds a critical one, the coercivities of the core, the surface shell and the system become zero.

  • 121.
    El Hamri, M.
    et al.
    Univ Moulay Ismail, CNRST URAC 08, Lab Phys Mat & Modelisat Syst LP2MS, Fac Sci,Phys Dept, BP 11201, Meknes, Morocco..
    Bouhou, S.
    Univ Moulay Ismail, CNRST URAC 08, Lab Phys Mat & Modelisat Syst LP2MS, Fac Sci,Phys Dept, BP 11201, Meknes, Morocco..
    Essaoudi, I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Ainane, A.
    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, Molecular and Condensed Matter Physics.
    Dujardin, F.
    Univ Lorraine, LCP A2MC, Inst Chim Phys & Mat, 1 Bd Arago, F-57070 Metz, France..
    Hysteresis loop behaviors of a decorated double-walled cubic nanotube2017In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 524, p. 137-143Article in journal (Refereed)
    Abstract [en]

    The effect of surface shell parameters on the hysteresis loop behaviors of a decorated Ising cubic nanotube, consisting of a ferromagnetic spin-12 core which is interacting ferrimagnetically with a ferromagnetic spin-1 surface shell, is investigated, in the present work, within the effective-field theory with correlations based on the probability distribution technique. We have found that these parameters have a strong effect on the shape and the number of hysteresis loops and also on the coercive field and remanent magnetization behaviors. Indeed, triple, quintuple, septuple and nonuple hysteresis loop patterns have also been observed.

  • 122.
    El Hamri, M.
    et al.
    Univ Moulay Ismail, LP2MS, Fac Sci, CNRST URAC 08,Unite Associee,Phys Dept, BP 11201, Meknes, Morocco..
    Bouhou, S.
    Univ Moulay Ismail, LP2MS, Fac Sci, CNRST URAC 08,Unite Associee,Phys Dept, BP 11201, Meknes, Morocco..
    Essaoudi, I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Univ Moulay Ismail, LP2MS, Fac Sci, CNRST URAC 08,Unite Associee,Phys Dept, BP 11201, Meknes, Morocco..
    Ainane, Abdelmajid
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Univ Moulay Ismail, LP2MS, Fac Sci, CNRST URAC 08,Unite Associee,Phys Dept, BP 11201, Meknes, Morocco.;Max Planck Inst Phys Complexer Syst, Nothnitzer Str 38, D-01187 Dresden, Germany.; Univ Lorraine, LCP A2MC, Inst Chim Phys & Mat, 1 Bd Arago, F-57070 Metz, France..
    Ahuja, R
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Dujardin, F.
    Univ Lorraine, LCP A2MC, Inst Chim Phys & Mat, 1 Bd Arago, F-57070 Metz, France..
    Magnetic behaviors of a transverse spin-1/2 Ising cubic nanowire with core/shell structure2017In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 507, p. 51-60Article in journal (Refereed)
    Abstract [en]

    The surface shell exchange coupling effect on the magnetic properties (surface shell, core, total longitudinal and total transverse magnetizations, susceptibility, phase diagram and hysteresis loops) of a transverse spin-1/2 Ising cubic nanowire is investigated, in the present work, by employing the effective-field theory based on the probability distribution technique with correlations, for both ferro-and antiferromagnetic cases. We have found that this parameter has a strong effect on the magnetic properties in both cases. In the ferromagnetic case, the total longitudinal magnetization curves display Q-and S-type behaviors and the hysteresis loop has just one loop, whereas in the antiferromagnetic case, the N-type behavior, in which one compensation temperature appears below the critical temperature, exists in the total longitudinal magnetization curve versus reduced temperature, and triple hysteresis loops are found. The effect of applied field is also investigated on the total longitudinal magnetization for the both cases, and we have found that a large applied field value can overcome the antiferromagnetic coupling leading to a ferromagnetic-like behavior.

  • 123. El Hamri, M.
    et al.
    Bouhou, S.
    Essaoudi, I.
    Ainane, Abdelmajid
    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.
    Investigation of the surface shell effects on the magnetic properties of a transverse antiferromagnetic Ising nanocube2015In: Superlattices and Microstructures, ISSN 0749-6036, E-ISSN 1096-3677, Vol. 80, p. 151-168Article in journal (Refereed)
    Abstract [en]

    The effective-field theory (EFT) with correlations based on the probability distribution technique has been used to study the magnetic properties of an antiferromagnetic cubic nanoparticle (nanocube). We have found that the surface shell parameters have strong effects on the compensation temperature, the magnetization profiles, coercivity, the shape and the number of the hysteresis loops for certain parameters. The effect of reduced temperature has also been examined on the hysteresis loops.

  • 124.
    El Hamri, M.
    et al.
    Univ Moulay Ismail, LP2MS, Unite Associee CNRST URAC 08, Dept Phys,Fac Sci, Meknes, Morocco..
    Bouhou, S.
    Univ Moulay Ismail, LP2MS, Unite Associee CNRST URAC 08, Dept Phys,Fac Sci, Meknes, Morocco..
    Essaoudi, I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Univ Moulay Ismail, LP2MS, Unite Associee CNRST URAC 08, Dept Phys,Fac Sci, Meknes, Morocco..
    Ainane, Abdelmajid
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Univ Moulay Ismail, LP2MS, Unite Associee CNRST URAC 08, Dept Phys,Fac Sci, Meknes, Morocco.;Max Planck Inst Phys Complexer Syst, D-01187 Dresden, Germany..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Magnetic properties of a diluted spin-1/2 Ising nanocube2016In: Physica A: Statistical Mechanics and its Applications, ISSN 0378-4371, E-ISSN 1873-2119, Vol. 443, p. 385-398Article in journal (Refereed)
    Abstract [en]

    The effective-field theory with correlations based on the probability distribution technique is used to investigate the magnetic properties of a diluted Ising nanocube consisting of a ferromagnetic spin-1/2 core which is interacting antiferromagnetically with a ferromagnetic spin-1/2 surface shell. The effect of the concentration of magnetic atoms is examined. A number of interesting phenomena have been found such as the existence of the compensation temperature and triple hysteresis loops.

  • 125.
    El Hamri, M.
    et al.
    Univ Moulay Ismail, Unite Associee CNRST URAC 08, LP2MS, BP 11201, Meknes, Morocco..
    Bouhou, S.
    Univ Moulay Ismail, Unite Associee CNRST URAC 08, LP2MS, BP 11201, Meknes, Morocco..
    Essaoudi, I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Univ Moulay Ismail, Unite Associee CNRST URAC 08, LP2MS, BP 11201, Meknes, Morocco..
    Ainane, Abdelmajid
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Univ Moulay Ismail, Unite Associee CNRST URAC 08, LP2MS, BP 11201, Meknes, Morocco.;Max Planck Inst Phys Complexer Syst, Nothnitzer Str 38, D-01187 Dresden, Germany..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Magnetic Properties of a Diluted Transverse Spin-1 Ising Nanocube with a Longitudinal Crystal-Field2017In: INTERNATIONAL SYMPOSIUM ON CLUSTERS AND NANOMATERIALS / [ed] Jena, P Kandalam, AK, SPIE-INT SOC OPTICAL ENGINEERING , 2017, article id UNSP 1017409-1Conference paper (Refereed)
    Abstract [en]

    In the present work, the effective field theory with correlations based on the probability distribution technique has been used to investigate the effect of the surface shell longitudinal cristal field on the magnetic properties of a diluted antiferromagnetic spin-1 Ising nanocube particle. This effect has also been studied on the hysteresis loops of the system. It is found that this parameter has a strong effect on the magnetization profiles, compensation temperature, coercive field and remanent magnetization.

  • 126.
    El Hamri, M.
    et al.
    Univ Moulay Ismail, Fac Sci, Dept Phys,Unite Associee CNRST URAC 08, Lab Phys Mat & Modelisat Syst LP2MS, BP 11201, Meknes, Morocco..
    Bouhou, S.
    Univ Moulay Ismail, Fac Sci, Dept Phys,Unite Associee CNRST URAC 08, Lab Phys Mat & Modelisat Syst LP2MS, BP 11201, Meknes, Morocco..
    Essaoudi, I.
    Univ Moulay Ismail, Fac Sci, Dept Phys,Unite Associee CNRST URAC 08, Lab Phys Mat & Modelisat Syst LP2MS, BP 11201, Meknes, Morocco..
    Ainane, Abdelmajid
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Univ Moulay Ismail, Fac Sci, Dept Phys,Unite Associee CNRST URAC 08, Lab Phys Mat & Modelisat Syst LP2MS, BP 11201, Meknes, Morocco.;Max Planck Inst Phys Complexer Syst, Nothnitzer Str 38, D-01187 Dresden, Germany..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Dujardin, F.
    ICPM, Lab Chim & Phys LCP A2MC, 1 Bd Arago, F-57070 Metz, France..
    Phase diagrams of a transverse cubic nanowire with diluted surface shell2016In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 122, no 3, article id 202Article in journal (Refereed)
    Abstract [en]

    The effective-field theory with correlations based on the probability distribution technique has been used to investigate the phase diagrams (critical and compensation temperatures) of a transverse antiferromagnetic spin-1/2 Ising cubic nanowire with diluted surface shell. It is found that the phase diagrams of the system are strongly affected by the surface shell parameters. Indeed, two compensation points appear for certain values of Hamiltonian parameters, and the range of appearance of these latter points depends strongly on the surface shell transverse field.

  • 127.
    El Hamri, M.
    et al.
    Univ Moulay Ismail, Dept Phys, Fac Sci, LP2MS,Unite Associee CNRST URAC 08, BP 11201, Meknes, Morocco..
    Bouhou, S.
    Univ Moulay Ismail, Dept Phys, Fac Sci, LP2MS,Unite Associee CNRST URAC 08, BP 11201, Meknes, Morocco..
    Essaoudi, I.
    Univ Moulay Ismail, Dept Phys, Fac Sci, LP2MS,Unite Associee CNRST URAC 08, BP 11201, Meknes, Morocco..
    Ainane, Abdelmajid
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Univ Moulay Ismail, Dept Phys, Fac Sci, LP2MS,Unite Associee CNRST URAC 08, BP 11201, Meknes, Morocco.;Max Planck Inst Phys Complexer Syst, Nothnitzer Str 38, D-01187 Dresden, Germany.;Univ Lorraine, LCP A2MC, Inst Chim Phys & Mat, 1 Bd Arago, F-57070 Metz, France..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Dujardin, F.
    Univ Lorraine, LCP A2MC, Inst Chim Phys & Mat, 1 Bd Arago, F-57070 Metz, France..
    Some characteristic behaviours of a spin-1/2 Ising nanoparticle2016In: 3Rd Euro-Mediterranean Conference On Materials And Renewable Energies (Emcmre-3), IOP PUBLISHING LTD , 2016, article id UNSP 012023Conference paper (Refereed)
    Abstract [en]

    By using the effective-field theory with correlations based on the probability distribution technique; the magnetization, susceptibility, internal energy, specific heat and the free energy expressions for a ferromagnetic spin-1/2 Ising nanoparticle have been developed and calculated numerically for different surface shell exchange coupling parameter. A number of interesting phenomena have been observed, depending on the surface shell exchange coupling term.

  • 128.
    El Hamri, M.
    et al.
    Univ Moulay, Fac Sci, Unite Associee CNRST URAC 08, Syst,LP2MS,Dept Phys,Lab Phys Mat & Modelisat, Ismail, Meknes, Morocco..
    Bouhou, S.
    Univ Moulay, Fac Sci, Unite Associee CNRST URAC 08, Syst,LP2MS,Dept Phys,Lab Phys Mat & Modelisat, Ismail, Meknes, Morocco..
    Essaoudi, I.
    Univ Moulay, Fac Sci, Unite Associee CNRST URAC 08, Syst,LP2MS,Dept Phys,Lab Phys Mat & Modelisat, Ismail, Meknes, Morocco..
    Ainane, Abdelmajid
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Univ Moulay, Fac Sci, Unite Associee CNRST URAC 08, Syst,LP2MS,Dept Phys,Lab Phys Mat & Modelisat, Ismail, Meknes, Morocco.;Max Planck Inst Phys Complexer Syst, D-01187 Dresden, Germany..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Dujardin, F.
    ICPM, LCPMC, F-57070 Metz, France..
    Thermodynamic Properties of the Core/Shell Antiferromagnetic Ising Nanocube2015In: Journal of Superconductivity and Novel Magnetism, ISSN 1557-1939, E-ISSN 1557-1947, Vol. 28, no 10, p. 3127-3133Article in journal (Refereed)
    Abstract [en]

    Using the effective field theory with correlations, the effects of the exchange interaction on the thermal behaviors of the total magnetization, internal energy, specific heat, entropy, and free energy of a transverse antiferromagnetic Ising nanocube are investigated. The phase diagram is also calculated and discussed in detail.

  • 129.
    Emanuelsson, Rikard
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Löfås, Henrik
    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 Chemistry - BMC, Physical Organic Chemistry. Institut für Anorganische Chemie, Technische Universität Graz.
    Nauroozi, Djawed
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Baumgartner, Judith
    Institut für Anorganische Chemie, Technische Universität Graz.
    Marschner, Christoph
    Institut für Anorganische Chemie, Technische Universität Graz.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ott, Sascha
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Grigoriev, Anton
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Configuration- and Conformation-Dependent Electronic Structure Variations in 1,4-Disubstituted Cyclohexanes Enabled by a Carbon-to-Silicon Exchange2014In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 20, no 30, p. 9304-9311Article in journal (Other academic)
    Abstract [en]

    Cyclohexane, with its well-defined conformers, could be an ideal force-controlled molecular switch if it were to display substantial differences in electronic and optical properties between its conformers. We utilize sigma conjugation in heavier analogues of cyclohexanes (i.e. cyclohexasilanes) and show that 1,4-disubstituted cyclohexasilanes display configuration-and conformation-dependent variations in these properties. Cis- and trans-1,4-bis(trimethylsilylethynyl)-cyclohexasilanes display a 0.11 V difference in their oxidation potentials (computed 0.11 V) and a 0.34 eV difference in their lowest UV absorption (computed difference between first excitations 0.07 eV). This is in stark contrast to differences in the corresponding properties of analogous all-carbon cyclohexanes (computed 0.02 V and 0.03 eV, respectively). Moreover, the two chair conformers of the cyclohexasilane trans isomer display large differences in electronic-structure-related properties. This enables computational design of a mechanically force-controlled conductance switch with a calculated single-molecule ON/OFF ratio of 213 at zero-bias voltage.

  • 130.
    Emanuelsson, Rikard
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Löfås, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Zhu, Jun
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry. State Key Laboratory of Physical Chemistry of Solid Surfaces, Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry, Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University.
    Ahuja, Rajeev
    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.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    In Search of Flexible Molecular Wires with Near Conformer-Independent Conjugation and Conductance: A Computational Study2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 11, p. 5637-5649Article in journal (Refereed)
    Abstract [en]

    Oligomers of 1,4-disila/germa/stannacyclohexa-2,5-dienes as well as all-carbon 1,4-cyclohexadienes connected via E—E single bonds (E = C, Si, Ge, or Sn) were studied through quantum chemical calculations in an effort to identify conformationally flexible molecular wires that act as molecular “electrical cords” having conformer-independent conjugative and conductive properties. Our oligomers display neutral hyperconjugative interactions (σ/π-conjugation) between adjacent σ(E—E) and π(C═C) bond orbitals, and these interactions do not change with conformation. The energies and spatial distributions of the highest occupied molecular orbitals of methyl-, silyl-, and trimethylsilyl (TMS)-substituted 1,4-disilacyclohexa-2,5-diene dimers, and stable conformers of trimers and tetramers, remain rather constant upon Si–Si bond rotation. Yet, steric congestion may be a concern in some of the oligomer types. The calculated conductances for the Si-containing tetramers are similar to that of a σ-conjugated linear all-anti oligosilane (a hexadecasilane) with equally many bonds in the conjugated paths. Moreover, the Me-substituted 1,4-disilacyclohexadiene tetramer has modest conductance fluctuations with Si–Si bond rotations when the electrode–electrode distance is locked (variation by factor 30), while the fluctuations under similar conditions are larger for the analogous TMS-substituted tetramer. When the electrode–electrode distance is changed several oligomers display small conductance variations within certain distance intervals, e.g., the mean conductance of TMS-substituted 1,4-disilacyclohexa-2,5-diene tetramer is almost unchanged over 9 Å of electrode–electrode distances.

  • 131.
    Fang, C. M.
    et al.
    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.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Prediction of MAX phases, VN+1SiCN (N=1,2), from first-principles theory2007In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, no 1, p. 013511-Article in journal (Refereed)
    Abstract [en]

    We have investigated the phase stability of two MAX phases, V3SiC2 and V2SiC, by means of first-principles total-energy calculations within the generalized-gradient approximation and the projector-augmented wave method. The theoretical bulk modulus of V3SiC2 is 219 GPa, which is similar to 17% larger than that of Ti3SiC2 (187 GPa). The total-energy calculations show that V2SiC is stable with a formation energy of about 0.27 eVf.u. and that V3SiC2 is metastable (only 0.02 eVf.u. is required to stabilize this phase from its competing phases). We suggest that both these two MAX compounds should be possible to synthesize as stable (or metastable) phases using, e.g., thin-film deposition.

  • 132.
    Fang, Changming
    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.
    Local structure and electronic-spin transition of Fe-bearing MgSiO3 perovskite under conditions of the Earth's lower mantle2008In: Physics of the Earth and Planetary Interiors, ISSN 0031-9201, E-ISSN 1872-7395, Vol. 166, no 1-2, p. 77-82Article in journal (Refereed)
    Abstract [en]

    We report first-principles electronic structure calculations on the structural and electronic-spin behaviours of Fe-bearing MgSiO3 crystals up to the pressure of Earth's mantle. The transition pressure of the Fe-bearing MgSiO3 from the orthorhombic perovskite (OPv) to the orthorhombic post-perovskite (OPPv) phase decreases with increasing Fe concentration. The lattice distortion has impacts on the electronic-spin behaviour of the Fe ions in the PVs. The spin-polarizations of the Fe ions in the (Fe,Mg)SiO3 OPvs and OPPvs keep unchanged up to the pressures in the lower mantle. Meanwhile, the Fe-bearing MgSiO3 OPV Containing Fe-Mg-Fe-Si pairs exhibits multiple-magnetic moments co-existing in a large pressure range (from about 78 to 110 GPa), and finally becomes non-magnetic at pressure higher than 110 GPa. These results provide a mechanism to understand the recent experimental results about Fe valence states and the electronic transitions of the Fe-bearing MgSiO3 under high pressure.

  • 133.
    Fang, Chang-Ming
    et al.
    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.
    Structures and stability of ABO(3) orthorhombic perovskites at the Earth's mantle conditions from first-principles theory2006In: Physics of the Earth and Planetary Interiors, ISSN 0031-9201, E-ISSN 1872-7395, Vol. 157, no 1-2, p. 1-7Article in journal (Refereed)
    Abstract [en]

    We report first-principles calculations on the structures and stabilities of the ABO(3) (A = Mg and Ca; B = Si and Ge) orthorhombic perovskites (OPvs) under high pressures. Calculations have also been performed for CdGeO3 and CdTiO3 OPvs. The calculations showed that MgSiO3, MgGeO3, CaGeO3, CdGeO3 and CdTiO3 OPvs transform to the orthorhombic post-perovskites (OPPvs) at about 10 1, 47, 55, 78 and 64 GPa, respectively, while CaSiO3 OPv is stable under high pressures. The theoretical results are in good agreement with the available experiments. The lattice distortions with pressure have been studied by analyzing the lattice deviations from the corresponding cubic perovskite (CPv). The lattice distortions increase with pressure for MgSiO3, MgGeO3, CaGeO3 and CdTiO3 OPvs, while CaSiO3 OPv has very small lattice distortions under high-pressures and the lattice distortions of CdGeO3 OPV even decrease with increasing pressure. The OPPvs have large distortions for the a-axis (about -10%).

  • 134.
    Fang, C.M.
    et al.
    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.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Li, S.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Jansson, Ulf
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry.
    Wilhelmsson, Ola
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry.
    Hultman, L.
    General trend of the mechanical properties of the ternary carbides M3SiC2 (M=transition metal)2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, no 5, p. 054106-Article in journal (Refereed)
    Abstract [en]

    We present results from first-principles calculations of ternary transition metal carbides in the M3SiC2 series (where M=early transition metal). We predict structural and mechanical properties of these new MN+1AXN phases. The bulk modulus of the ternary carbides, M3SiC2, are in the calculations found to be proportional to the bulk modulus of the corresponding binary carbides, MC. We have analyzed this behavior using a simple, nearest-neighbor bond model, as well as from first-principles total energy calculations and have found that it is caused by a considerably weaker M-Si bond compared to the M-C bond.

  • 135.
    G.E. Grechnev,
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics IV. Theoretical Magnetism. TEORETISK MAGNETISM.
    Ahuja, Rajeev
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics IV. Theoretical Magnetism. Kondenserade materiens teori.
    Johansson, Börje
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics IV. Theoretical Magnetism. Kondenserade materiens teori.
    Eriksson, Olle
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics IV. Theoretical Magnetism. Teoretisk magnetism.
    Electronic structure and magnetic properties of Lithium manganese spinels2003In: J.Magn. Magn. Matt., Vol. 258, p. 285-Article in journal (Refereed)
    Abstract [en]

    Electronic and magnetic structures of the spinel-type lithium–manganese oxides LixMn2O4, x=0,0.5,1, are studied ab initio by employing a full-potential LMTO method. The effect of the orthorhombic distortion on electronic structure and magnetism of LiMn2O4 was investigated, and our calculations do not show a substantial charge ordering at the structural transition from the cubic spinel to the orthorhombic structure.

  • 136. Glans, P. -A
    et al.
    Learmonth, T.
    Smith, K. E.
    Ferro, S.
    De Battisti, A.
    Mattesini, M.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Guo, J. -H
    Electronic structure of boron doped diamond: An x-ray spectroscopic study2013In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 102, no 16, p. 162103-Article in journal (Refereed)
    Abstract [en]

    The valence and conduction band electronic structure of boron-doped diamond has been measured using soft x-ray emission and absorption spectroscopy. The experimental results reveal p-type doping in the diamond film through the appearance of states in the band-gap. Structure distortion was observed around the doping center, while the long range order of the diamond structure remains. A chemically shifted C 1s level explains why one of the absorption features seems to appear below the valence band maximum. An excitonic feature was observed in the boron-doped diamond, similar to that observed in pure diamond, indicating that the exciton binding energy remains the same upon B-doping. 

  • 137.
    Gond, Ritambhara
    et al.
    Indian Inst Sci, Bangalore .
    Meena, Sher Singh
    Bhabha Atom Res Ctr, Bombay .
    Yusuf, S. M.
    Bhabha Atom Res Ctr, Bombay .
    Shukla, Vivekanand
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Jena, Naresh K.
    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.
    Okada, Shigeto
    Kyushu Univ, Japan.
    Barpanda, Prabeer
    Indian Inst Sci, Bangalore.
    Enabling the Electrochemical Activity in Sodium Iron Metaphosphate [NaFe(PO3)(3)] Sodium Battery Insertion Material: Structural and Electrochemical Insights2017In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 56, no 10, p. 5918-5929Article in journal (Refereed)
    Abstract [en]

    Sodium-ion batteries are widely pursued as an economic alternative to lithium-ion battery technology, where Fe- and Mn-based compounds are particularly attractive owing to their elemental abundance. Pursuing phosphate-based polyanionic chemistry, recently solid-state prepared NaFe(PO3)(3) metaphosphate was unveiled as a novel potential sodium insertion material, although it was found to be electrochemically inactive. In the current work, employing energy-savvy solution combustion synthesis, NaFe2+(PO3)(3) was produced from low-cost Fe3+ precursors. Owing to the formation of nanoscale carbon-coated product, electrochemical activity was enabled in NaFe(PO3)(3) for the first time. In congruence with the first principles density functional theory (DFT) calculations, an Fe3+/Fe2+ redox activity centered at 2.8 V (vs Na/Na+) was observed. Further, the solid-solution metaphosphate family Na(Fe1-xMnx)(PO3)(3) (x = 0-1) was prepared for the first time. Their structure and distribution of transition metals (TM = Fe/Mn) was analyzed with synchrotron diffraction, X-ray photoelectron spectroscopy, and Mossbauer spectroscopy. Synergizing experimental and computational tools, NaFe(PO3)(3) metaphosphate is presented as an electrochemically active sodium insertion host material.

  • 138. Gowtham, S.
    et al.
    Scheicher, Ralph H.
    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.
    Pandey, Ravindra
    Karna, Shashi P.
    Physisorption of nucleobases on graphene: Density-functional calculations2007In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 76, no 3, p. 033401-Article in journal (Refereed)
    Abstract [en]

    We report the results of our first-principles investigation on the interaction of the nucleobases adenine (A), cytosine (C), guanine (G), thymine (T), and uracil (U) with graphene, carried out within the density-functional theory framework, with additional calculations utilizing Hartree-Fock plus second-order Møller-Plesset perturbation theory. The calculated binding energy of the nucleobases shows the following hierarchy: G>A~T~C>U, with the equilibrium configuration being rather similar for all five of them. Our results clearly demonstrate that the nucleobases exhibit significantly different interaction strengths when physisorbed on graphene. The stabilizing factor in the interaction between the base molecule and graphene sheet is dominated by the molecular polarizability that allows a weakly attractive dispersion force to be induced between them. The present study represents a significant step toward a first-principles understanding of how the base sequence of DNA can affect its interaction with carbon nanotubes, as observed experimentally.

  • 139. Gowtham, S.
    et al.
    Scheicher, Ralph H.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Pandey, Ravindra
    Karna, Shashi P.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    First-principles study of physisorption of nucleic acid bases on small-diameter carbon nanotubes2008In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 19, no 12, p. 125701-Article in journal (Refereed)
    Abstract [en]

    We report the results of our first-principles study based on density functional theory on the interaction of the nucleic acid base molecules adenine (A), cytosine (C), guanine (G), thymine (T), and uracil (U), with a single-walled carbon nanotube (CNT). Specifically, the focus is on the physisorption of base molecules on the outer wall of a (5, 0) metallic CNT possessing one of the smallest diameters possible. Compared to the case for CNTs with large diameters, the physisorption energy is found to be reduced in the high-curvature case. The base molecules exhibit significantly different interaction strengths and the calculated binding energies follow the hierarchy G>A>T>C>U, which appears to be independent of the tube curvature. The stabilizing factor in the interaction between the base molecule and CNT is dominated by the molecular polarizability that allows a weakly attractive dispersion force to be induced between them. The present study provides an improved understanding of the role of the base sequence in deoxyribonucleic acid (DNA) or ribonucleic acid (RNA) in their interactions with carbon nanotubes of varying diameters.

  • 140.
    Grechnev, Alexei
    et al.
    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.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Balanced crystal orbital overlap population: a tool for analysing chemical bonds in solids2003In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 15, no 45, p. 7751-7761Article in journal (Refereed)
    Abstract [en]

    A new tool for analysing theoretically the chemical bonding in solids is proposed. A balanced crystal orbital overlap population (BCOOP) is an energy resolved quantity which is positive for bonding states and negative for antibonding states, hence enabling a distinction between bonding and antibonding contributions to the chemical bond. Unlike the conventional crystal orbital overlap population (COOP), BCOOP handles correctly the situation of crystal orbitals being nearly linear dependent, which is often the case in the solid state. Also, BCOOP is much less basis set dependent than COOP. A BCOOP implementation within the full-potential linear muffin tin orbital method is presented and illustrated for Si, TiC and Ru. Thus, BCOOP is compared to the COOP and crystal orbital Hamilton population (COHP) for systems with chemical bonds ranging from metallic to covalent character.

  • 141.
    Grechnev, Alexei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Andersson, Per H.
    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.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Vennström, Marie
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry.
    Andersson, Yvonne
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry.
    H-H interaction and structural phase transition in Ti3SnHx2002In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 66, no 23, p. 235104-Article in journal (Refereed)
  • 142.
    Grechnev, Alexei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Li, Sa
    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.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Jansson, Ulf
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry.
    Wilhelmsson, Ola
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry.
    Layered compound Nb3SiC2 predicted from first-principles theory2004In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 85, no 15, p. 3071-3073Article in journal (Refereed)
    Abstract [en]

    A previously unobserved ternary carbide, Nb3SiC2, belonging to the family of the so-called Mn+1AXn or MAX phases is predicted from first-principles calculations. It has a theoretical bulk modulus of 296 Gpa, wich is much higher than that of Ti3SiC2. The new phase is metastable with a formation energy of +0.02 eV/atom. We suggest that the phase may possibly be synthesized using thin film technology. The chemical binding of Nb3SiC2 is investigated using the balanced crystal orbital overlap population indicator and it is found to be dominated by the formation of Nb4D-C 2p covalent bonds.

  • 143. Grechnev, G. E.
    et al.
    Ahuja, Rajeev
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics and Materials Science, Theoretical Magnetism.
    Eriksson, Olle
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics and Materials Science, Theoretical Magnetism.
    Magnetic susceptibility of hcp iron and the seismic anisotropy of Earth's inner core2003In: PHYSICAL REVIEW B, ISSN 1098-0121, Vol. 68, no 6, p. 064414-Article in journal (Refereed)
    Abstract [en]

    The seismic anisotropy of the Earth's core is believed to be due to a preferred orientation of hexagonal close packed (hcp) iron crystals that constitute the dominating element in the inner core. In this connection, the magnetic properties of the hcp iron in an external magnetic field are very interesting and are studied here by employing an ab initio full-potential linear muffin tin orbital method. By this means the magnetic susceptibility chi of hcp iron and its anisotropy energy for pressures and temperatures corresponding to the Earth's inner core conditions have been evaluated in the framework of the local spin density approximation. The accuracy of this method has been validated by calculating the anisotropic susceptibility of paramagnetic transition metals that form in the hcp crystal structure at ambient conditions. Our calculations demonstrate that for hcp iron the anisotropy of chi is dependent on the c/a ratio. In conjunction with recent data on the c/a ratio and elastic constants of hcp iron, the magnetic anisotropy can explain the seismic anisotropy of the Earth's inner core.

  • 144.
    Grigoriev, Anton
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Simak, S. I.
    Wendin, G.
    Johansson, Börje
    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.
    Electron transport in stretched monoatomic gold wires2006In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 97, no 23, p. 236807-Article in journal (Refereed)
    Abstract [en]

    The conductance of monoatomic gold wires containing 3-7 gold atoms has been obtained from ab initio calculations. The transmission is found to vary significantly depending on the wire stretching and the number of incorporated atoms. Such oscillations are determined by the electronic structure of the one-dimensional (1D) part of the wire between the contacts. Our results indicate that the conductivity of 1D wires can be suppressed without breaking the contact.

  • 145.
    Guo, J H
    et al.
    Fysik II.
    Vayssieres, L
    Persson, C
    Ahuja, R
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics II. Physics IV. Fysik IV.
    Johansson, B
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics II. Physics IV. Fysik IV.
    Nordgren, J
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics II. Physics IV. Fysik II.
    Polarization-dependent soft-x-ray absorption of highly oriented ZnO microrod arrays2002In: Journal of Physics-Condensed Matter, Vol. 14, no 28, p. 6969-6974Article in journal (Refereed)
  • 146.
    Guo, J-H
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Gupta, Amita
    Sharma, Parmanand
    Rao, K. V.
    Marcus, M. A.
    Dong, C. L.
    Guillen, J. M. Osorio
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Butorin, Sergei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Mattesini, Maurizio
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Glans, P. A.
    Smith, K. E.
    Chang, C. L.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    X-ray spectroscopic study of the charge state and local ordering of room-temperature ferromagnetic Mn-doped ZnO2007In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 19, no 17, p. 172202-Article in journal (Refereed)
    Abstract [en]

    The charge state and local ordering of Mn doped into a pulsed laser deposited single-phase thin film of ZnO are investigated by using x-ray absorption spectroscopy at the O K-edge, Mn K-edge and L-edge, and x-ray emission spectroscopy at the O K-edge and Mn L-edge. This film is ferromagnetic at room temperature. EXAFS measurement shows that Mn2+ replaces the Zn site in tetrahedral symmetry, and there is no evidence for either metallic Mn or MnO in the film. Upon Mn doping, the top of O 2p valence band extends into the bandgap, indicating additional charge carriers being created.

  • 147. Guo, Jinghua
    et al.
    Vayssieres, L
    Persson, C
    Ahuja, Rajeev
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics IV. Physics II.
    Johansson, Börje
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics IV. Physics II.
    Nordgren, Joseph
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics IV. Physics II.
    Polarization-dependent soft-x-ray absorption of a highly oriented ZnO microrod-array2005In: Journal of Physics-Condensed Matter, ISSN 1361-648X, Vol. 17, no 1, p. 235-240Article in journal (Refereed)
    Abstract [en]

    We report the soft-X-ray absorption and emission studies of NaCl, MgCl2, and AlCl3 in water solutions. The influences of cations on the water molecular structure can be seen as the absorption threshold edge shifted to high energy in the X-ray absorption spectra; the mixing of molecular orbital in 3a1 symmetry is reinforced as the intensity of 3a1 is further reduced; and the 1b1-emission peak shows the broadening and shift differently for Na+, Mg2+, and Al3+ water solutions, which indicates that the charge difference of the cations may not be the only playing role being responsible to the interactions between the cations and water molecules.

  • 148. Guo, Zhonglu
    et al.
    Sa, Baisheng
    Pathak, Biswarup
    Zhou, Jian
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Sun, Zhimei
    Band gap engineering in huge-gap semiconductor SrZrO3 for visible-light photocatalysis2014In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 39, no 5, p. 2042-2048Article in journal (Refereed)
    Abstract [en]

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

  • 149. Gupta, A
    et al.
    Ahuja, Rajeev
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    High Temperature Ferromagnetism in Gallium Phosphide Doped with copper2006In: Phys. Rev. B, Vol. 74, p. 224449-Article in journal (Refereed)
  • 150. Gupta, Amita
    et al.
    Owens, Frank J.
    Rao, K. V.
    Iqbal, Zafar
    Guille, J. M. Osorio
    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.
    High-temperature ferromagnetism in Cu-doped GaP by SQUID magnetometry and ferromagnetic resonance measurements2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, no 22, p. 224449-Article in journal (Refereed)
    Abstract [en]

    The search for ferromagnetism above room temperature in semiconductors doped with paramagnetic ions has intensified in recent years because of the potential of combining magnetic information storage and electronic switching in one spintronic device. Here we report an observation of ferromagnetism well above room temperature in gallium phosphide doped with Cu2+ detected by ferromagnetic resonance and SQUID magnetometry. Other important features of the results in this p-type Cu-doped GaP are the high Curie temperature above 700 K significantly higher than previous observations, the relatively simple low-temperature bulk sintering process used to synthesize the material, which will significantly reduce the cost of large-scale production, and the use of copper as the dopant rather than manganese, which precludes ferromagnetic clusters or magnetic alloy impurities as the origin of the ferromagnetism. Ab initio calculations also show the existence of ferromagnetism in Cu-doped GaP. When the spin-orbit coupling is included, the total moment is enhanced and we get a total magnetic moment of 0.31 mu(B) with a local moment on Cu 0.082 and on P 0.204 mu(B).

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