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  • 1.
    Abdel-Hafiez, Mahmoud
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. Ctr High Pressure Sci & Technol Adv Res, Shanghai 201203, Peoples R China;Harvard Univ, Lyman Lab Phys, Cambridge, MA 02138 USA;Natl Univ Sci & Technol MISiS, Moscow 119049, Russia.
    Thiyagarajan, R.
    Ctr High Pressure Sci & Technol Adv Res, Shanghai 201203, Peoples R China.
    Majumdar, Arnab
    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.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Vasiliev, A. N.
    Natl Univ Sci & Technol MISiS, Moscow 119049, Russia;Natl Res South Ural State Univ, Chelyabinsk 454080, Russia;Moscow MV Lomonosov State Univ, Moscow 119991, Russia.
    Maarouf, A. A.
    Imam Abdulrahman Bin Faisal Univ, Inst Res & Med Consultat, Dept Phys, Dammam 31441, Saudi Arabia.
    Zybtsev, S. G.
    RAS, Inst Radioengn & Elect, Moscow 125009, Russia.
    Pokrovskii, V. Ya
    RAS, Inst Radioengn & Elect, Moscow 125009, Russia.
    V-Zaitsev-Zotov, S.
    RAS, Inst Radioengn & Elect, Moscow 125009, Russia.
    Pavlovskiy, V. V.
    RAS, Inst Radioengn & Elect, Moscow 125009, Russia.
    Pai, Woei Wu
    Natl Taiwan Univ, Ctr Condensed Matter Sci, Taipei 106, Taiwan;Natl Taiwan Univ, Dept Phys, Taipei 10610, Taiwan.
    Yang, W.
    Ctr High Pressure Sci & Technol Adv Res, Shanghai 201203, Peoples R China.
    Kulik, L. , V
    Pressure-induced reentrant transition in NbS3 phases: Combined Raman scattering and x-ray diffraction study2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 23, article id 235126Article in journal (Refereed)
    Abstract [en]

    We report the evolution of charge density wave states under pressure for two NbS3 phases: triclinic (phase I) and monoclinic (phase II) at room temperature. Raman and x-ray diffraction (XRD) techniques are applied. The x-ray studies on the monoclinic phase under pressure show a compression of the lattice at different rates below and above similar to 7 GPa but without a change in space group symmetry. The Raman spectra of the two phases evolve similarly with pressure; all peaks almost disappear in the similar to 6-8 GPa range, indicating a transition from an insulating to a metallic state, and peaks at new positions appear above 8 GPa. The results suggest suppression of the ambient charge-density waves and their subsequent recovery with new orderings above 8 GPa.

  • 2.
    Agåker, Marcus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics II.
    Käämbre, Tanel
    Glover, Chris
    Schmitt, Thorsten
    Mattesini, Maurizio
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Söderström, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Rubensson, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Resonant inelastic soft x-ray scattering at double core excitations in solid LiCl2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 73, no 24, article id 245111Article in journal (Refereed)
    Abstract [en]

    Inelastic soft x-ray scattering in LiCl, resonantly enhanced at states with two Li 1s vacancies, is investigated. States in which both excited electrons are localized during the double core hole lifetime, in which one of the electrons delocalize, as well as triply excited states in which the double core excitation is accompanied by a valence-to-conduction band excitation, contribute to the scattering. The angular momentum symmetry of the involved states and the vibronic coupling during the scattering process are reflected in the angular anisotropy. The effect on the local electronic structure of multiple core holes is theoretically studied by means of supercell band calculations.

  • 3.
    Agåker, Marcus
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics II. Physics IV.
    Söderström, Johan
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics II. Physics IV.
    Käämbre, Tanel
    Glover, C
    Gridneva, L
    Department of Physics and Materials Science, Physics II. Physics IV.
    Schmitt, Thorsten
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics II. Physics IV.
    Augustsson, Andreas
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics II. Physics IV.
    Mattesini, M
    Ahuja, Rajeev
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics II. Physics IV.
    Rubensson, Jan-Erik
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics II. Physics IV.
    Resonant inelastic soft X-ray scattering at hollow lithium states in solid LiCl2004In: Physical Review Letters, Vol. 93Article in journal (Refereed)
  • 4.
    Agåker, Marcus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics II.
    Söderström, Johan
    Käämbre, Tanel
    Glover, Chris
    Gridneva, Lidia
    Schmitt, Thorsten
    Augustsson, Andreas
    Mattesini, Maurizio
    Ahuja, Rajeev
    Rubensson, Jan-Erik
    Resonant Inelastic Soft X-ray Scattering at Hollow Lithium States in Solid LiCl2004In: Physical Review Letters, Vol. 93, no 1, p. 016404-Article in journal (Refereed)
  • 5.
    Ahmadivand, Arash
    et al.
    Rice Univ, Dept Elect & Comp Engn, 6100 Main St, Houston, TX 77005 USA.
    Gerislioglu, Burak
    Rice Univ, Dept Phys & Astron, 6100 Main St, Houston, TX 77005 USA.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Mishra, Yogendra Kumar
    Univ Kiel, Funct Nanomat, Inst Mat Sci, Kaiserstr 2, D-24143 Kiel, Germany.
    Terahertz plasmonics: The rise of toroidal metadevices towards immunobiosensings2020In: Materials Today, ISSN 1369-7021, E-ISSN 1873-4103, Vol. 32, p. 108-130Article, review/survey (Refereed)
    Abstract [en]

    This work reviews fundamentals and the recent state-of-art achievements in the field of plasmonic biosensing based terahertz (THz) spectroscopy. Being nonpoisonous and nondestructive to the human tissues, THz signals offer promising, cost-effective, and real-time biodevices for practical pharmaco-logical applications such as enzyme reaction analysis. Rapid developments in the field of THz plasmonics biosensors and immunosensors have brought many methodologies to employ the resonant subwavelength structures operating based on the fundamental physics of multipoles and asymmetric lineshape resonances. In the ongoing hunt for new and advanced THz plasmonic biosensors, the toroidal metasensors have emerged as excellent alternates and are introduced to be a very promising technology for THz immunosensing applications. Here, we provide examples of recently proposed THz plasmonic metasensors for the detection of thin films, chemical and biological substances. This review allows to compare the performance of various biosensing tools based on THz plasmonic approach and to understand the strategic role of toroidal metasensors in highly accurate and sensitive biosensors instrumentation. The possibility of using THz plasmonic biosensors based on toroidal technology in modern medical and clinical practices has been briefly discussed.

  • 6.
    Ahmadivand, Arash
    et al.
    Rice Univ, Dept Elect & Comp Engn, 6100 Main St, Houston, TX 77005 USA..
    Gerislioglu, Burak
    Rice Univ, Dept Phys & Astron, 6100 Main St, Houston, TX 77005 USA..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Uppsala Univ, Condensed Matter Theory Grp, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden..
    Mishra, Yogendra Kumar
    Univ Southern Denmark, Mads Clausen Inst, NanoSYD, Alsion 2, DK-6400 Sonderborg, Denmark..
    Toroidal Metaphotonics and Metadevices2020In: Laser & Photonics reviews, ISSN 1863-8880, E-ISSN 1863-8899, Vol. 14, no 11, article id 1900326Article, review/survey (Refereed)
    Abstract [en]

    Toroidal moments in artificial media have received growing attention and considered as a promising framework for initiating novel approaches to manage intrinsic radiative losses in nanophotonic and plasmonic systems. In the past decade, there has been substantial attention on the characteristics and excitation methods of toroidal multipoles-in particular, toroidal dipole-in 3D bulk and planar metaplatforms. The remarkable advantages of toroidal resonances have thrust the toroidal metasurface technology from relative anonymity into the limelight, in which researchers have recently centered on developing applied optical and optoelectronic subwavelength devices based on toroidal metaphotonics and metaplasmonics. In this focused contribution, the key principles of 3D and flatland toroidal metastructures are described, and the revolutionary tools that have been implemented based on this topology are briefly highlighted. Infrared photodetectors, immunobiosensors, ultraviolet beam sources, waveguides, and functional modulators are some of the fundamental and latest examples of toroidal metadevices that have been introduced and studied experimentally so far. The possibility of the realization of strong plexciton dynamics and pronounced vacuum Rabi oscillations in toroidal plasmonic metasurfaces are also presented in this review. Ultimate efficient extreme-subwavelength scale devices, such as low-threshold lasers and ultrafast switches, are thus in prospect.

  • 7. Ahuja, B. L.
    et al.
    Arora, G
    Ahmed, G
    Rathor, A
    Sharma, V
    Kádas, Krisztina
    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.
    A study of electron momentum density and charge transfer in W-Cu system2009In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 467, no 1-2, p. 595-599Article in journal (Refereed)
    Abstract [en]

    We present the first ever Compton scattering study on WxCu1-x(x=0.60, 0.72) alloys. The Compton profile measurements have been made using 20Ci (CS)-C-137 gamma-ray source. The experimental data are compared with the superposition of APW-based Compton profiles of constituent metals. A schematic study on charge transfer has been reported using the experimental valence band Compton profiles of both the alloys, W and Cu. Our first ever data support the charge transfer from W to Cu on alloying, which is also confirmed by our band structure calculations employing exact muffin-tin orbitals method (EMTO). (C) 2007 Elsevier B.V. All rights reserved.

  • 8.
    Ahuja, Rajeev
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics IV.
    Titanium metal at high pressure : Synchrotron experiments and ab initio calculations2004In: Phys. Rev. B, Vol. 69, p. 184102-Article in journal (Refereed)
  • 9.
    Ahuja, Rajeev
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Arwin, H.
    Ferreira da Silva, A.
    Persson, C.
    Osorio-Guillén, J. M.
    Souza de Almeida, J.
    Araujo, C. Moyses
    Veje, E.
    Veissid, N.
    An, C. Y.
    Electronic and optical properties of lead iodide2002In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 92, p. 7219-Article in journal (Refereed)
    Abstract [en]

    The electronic properties and the optical absorption of lead iodide (PbI2) have been investigated experimentally by means of optical absorption and spectroscopic ellipsometry, and theoretically by a full-potential linear muffin-tin-orbital method. PbI2 has been recognized as a very promising detector material with a large technological applicability. Its band-gap energy as a function of temperature has also been measured by optical absorption. The temperature dependence has been fitted by two different relations, and a discussion of these fittings is given.

  • 10.
    Ahuja, Rajeev
    et al.
    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.
    Larsson, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pyykkö, Pekka
    Zaleski-Ejgierd, Patryk
    Relativity and the lead–acid battery2011In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 106, no 1, p. 018301-Article in journal (Refereed)
    Abstract [en]

    The energies of the solid reactants in the lead-acid battery are calculated ab initio using two different basis sets at nonrelativistic, scalar-relativistic, and fully relativistic levels, and using several exchange-correlation potentials. The average calculated standard voltage is 2.13 V, compared with the experimental value of 2.11 V. All calculations agree in that 1.7-1.8 V of this standard voltage arise from relativistic effects, mainly from PbO2 but also from PbSO4.

  • 11.
    Ahuja, Rajeev
    et al.
    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, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    High-pressure structural transitions in Cm and Am0.5Cm0.5 binary alloy2006In: High Pressure Research, ISSN 0895-7959, E-ISSN 1477-2299, Vol. 26, no 4, p. 377-381Article in journal (Refereed)
    Abstract [en]

    The high-pressure behaviour of Cm and Am0.5Cm0.5 binary alloy is investigated theoretically using ab initio electronic structure methods. Our calculations reproduce the structural phase transitions, which are observed in recent experiment performed by Heathman et al. [S. Heathman, R.G. Haire, T. Le Bihan et al., Science 309 110 (2005)] and Lindbaum et al. [A. Lindbaum, S. Heathman, T. Le Bihan et al., J. Phys: Condens. Matter 15 S2297 (2003)]. Calculated transition pressures are in reasonable agreement with the experimental values. Calculations performed for an antiferromagnetic state are essential to reproduce the stability of Cm-III phase.

  • 12.
    Ahuja, Rajeev
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Sun, Z
    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.
    Ab initio investigation on the phase stability of Ti3SiC2, Ti3Si0.5Ge0.5C2 and2006In: High Pressure Research, Vol. 26, p. 127-Article in journal (Refereed)
  • 13.
    Allal, Adel
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Univ Amar Telidji, Lab Phys Mat, BP 37G, Laghouat 03000, Algeria..
    Bouchenafa, Mohamed
    Univ Amar Telidji, Fac Sci, Dept Sci Matiere, BP 37G, Laghouat 03000, Algeria.;Univ Blida 1, Theoret Phys & Radiat Matter Interact Lab LPTHIRM, Phys Dept, Blida, Algeria..
    Halit, Mohamed
    Univ Amar Telidji, Lab Phys Mat, BP 37G, Laghouat 03000, Algeria..
    Saib, Salima
    Univ Msila, Lab Mat Phys & Applicat, Msila 28000, Algeria..
    Liu, Zeliang
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Yanshan Univ, Coll Civil Engn & Mech, Qinhuangdao, Hebei, Peoples R China..
    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.
    Structural stability, mechanical, electronic and optical behaviour of RbXS2 (X = Y and La) under high pressure: A first-principle study2020In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 848, article id 156401Article in journal (Refereed)
    Abstract [en]

    The high-pressure behaviour of the ternary sulphides, RbXS2 (X = Y and La), has been investigated by using first-principle calculations based on density functional theory. Upon applying hydrostatic pressure, the unit-cell parameters (a, c) decrease with different rates, indicating an anisotropic axial compression. The most of RbYS2 and RbLaS2 crystals compressibility comes from Rb+1-S-2 bonds. Elastic constants and their dependence on pressure and related mechanical properties have been reported and analysed. From Pugh's criterion, RbYS2 and RbLaS2 turn from brittle to ductile material for applied pressures beyond 3.1 GPa and 2.9 GPa, respectively. Stability criteria show that RbYS2 and RbLaS2 are not mechanically stable in ci-NaFeO2 crystal structure above 20.63 GPa and 16.24 GPa, respectively. Both RbYS2 and RbLaS2 have indirect band gap, which decreases with increasing pressure. However, no indirectdirect band gap transition is observed for both materials. Finally, the calculated optical spectrum of both compounds exhibits an anisotropy and a broadening at high pressures.

  • 14.
    Allal, Adel
    et al.
    Univ Amar Telidji, Lab Phys Mat, BP 37G, Laghouat 03000, Algeria.
    Halit, Mohamed
    Univ Amar Telidji, Lab Phys Mat, BP 37G, Laghouat 03000, Algeria.
    Saib, Salima
    Univ Msila, Lab Mat Phys & Its Applicat, Msila 28000, Algeria.
    Azzouz, Lahcene
    Univ Amar Telidji, Lab Phys Mat, BP 37G, Laghouat 03000, Algeria.
    Maabed, Said
    Univ Amar Telidji, Fac Sci, Dept Sci Matiere, BP 37G, Laghouat 03000, Algeria.
    Bouchenafa, Mohamed
    Univ Amar Telidji, Fac Sci, Dept Sci Matiere, BP 37G, Laghouat 03000, Algeria;Univ Blida 1, Phys Dept, Fundamental & Appl Phys Lab, Blida, Algeria.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    A comparative theoretical investigation of optoelectronic and mechanical properties of KYS2 and KLaS22020In: Materials Science in Semiconductor Processing, ISSN 1369-8001, E-ISSN 1873-4081, Vol. 113, article id 105048Article in journal (Refereed)
    Abstract [en]

    The ternary sulfides KYS2 and KLaS2 are two promising candidates for numerous applications, as much as white LED, X-ray phosphor and transparent conductor materials. However, theoretical studies on these materials are lacking, and many of their physical properties are still unknown. The aim of this work is to investigate the physical properties of the ternary sulfides KYS2 and KLaS2 namely, structural, elastic, optoelectronic, thermodynamic analysis, and set the substitution effect of Y and La elements in the two compounds. The fundamental properties calculations are based on ab-initio pseudopotential framework, with both local density approximation (LDA) and generalized gradient approximations (GGA) along with an expanded set of plane waves. The Becke, 3-parameter, Lee–Yang–Parr (B3LYP) hybrid functional is also employed to describe the electronic structures and optical properties. The optimized crystal parameters are correlated very well with the existing experimental data. The predicted values of the elastic constants demonstrate that the two compounds are mechanically stable and can be classified as brittle materials. The band structure analysis reveals that both KYS2 and KLaS2 have indirect band gap. The optical properties, like the refractive index, extinction, absorption and reflectivity coefficients, are determined for various polarizations of incident light, while both compounds present optical anisotropy. The obtained optical properties indicate the high transparency of KYS2 and KLaS2 in the infrared and visible regions, which makes them promising candidates for many of transparent applications. The thermodynamic properties are investigated with the help of quasiharmonic Debye model approximation. KYS2 has a larger bulk modulus value, which make it more beneficial in engineering applications. Calculations of thermodynamical properties indicate that KYS2 compound has better thermal conductivity, stronger chemical bonds and bigger hardness.

  • 15.
    Allal, Adel
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Univ Amar Telidji, Lab Phys Materiaux, BP 37G, Laghouat 03000, Algeria..
    Halit, Mohamed
    Univ Amar Telidji, Lab Phys Materiaux, BP 37G, Laghouat 03000, Algeria..
    Saib, Salima
    Univ Msila, Lab Mat Phys & Its Applicat, Msila 28000, Algeria..
    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.
    Phase stability, phonon, electronic, and optical properties of not-yet-synthesized CsScS2, CsYS2, and APmS(2) (A= Li, Na, K, Rb, Cs) materials: Insights from first-principles calculations2022In: Materials Science in Semiconductor Processing, ISSN 1369-8001, E-ISSN 1873-4081, Vol. 150, article id 106936Article in journal (Refereed)
    Abstract [en]

    Transparent conducting materials (TCMs) combine two exclusive properties, electrical conductivity and visible light transparency; which make them a unique class of materials. They are required in a wide range of applications in modern life ranging from touchscreen-based devices, flat panel displays, light-emitting diodes (LED), and solar cells. Most of the commercially and widely used TCMs are n-type, whereas the development of highperformance p-type TCMs remains an outstanding challenge in the actual time. Herein, using the newly developed SCAN meta-GGA and the hybrid HSE06 functionals, we have explored the structural stability and physical properties of not-yet-synthesized ternary materials CsScS2, CsYS2, and APmS(2) (A = Li, Na, K, Rb, Cs) to identify promising p-type TCMs. As result, the calculated formation energy, phase diagram and phonon dispersion curves confirm that these materials are thermodynamically stable and feasible to synthesize experimentally. All these materials, have large optical band gaps (larger than 3.4 eV), small hole effective masses (except for LiPmS2), and have no absorption and weak reflectivity of the visible light. Our work demonstrates that these compounds have suitable properties for p-type TCMs applications.

  • 16.
    Alluri, Nagamalleswara Rao
    et al.
    Jeju Natl Univ, Fac Appl Energy Syst, Nanomat & Syst Lab, Major Mechatron Engn, Jeju 63243, South Korea.;Luxembourg Inst Sci & Technol, Mat Res & Technol Dept, 41 Rue Brill, L-4422 Belvaux, Luxembourg.;Interinst Res Grp Uni Lu LIST Ferro Mat, 41 Rue Brill, L-4422 Belvaux, Luxembourg..
    Raj, Nirmal Prashanth Maria Joseph
    Jeju Natl Univ, Fac Appl Energy Syst, Nanomat & Syst Lab, Major Mechatron Engn, Jeju 63243, South Korea..
    Khandelwal, Gaurav
    Jeju Natl Univ, Fac Appl Energy Syst, Nanomat & Syst Lab, Major Mechatron Engn, Jeju 63243, South Korea..
    Panda, Pritam Kumar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Banerjee, Amitava
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Mishra, Yogendra Kumar
    Univ Southern Denmark, Mads Clausen Inst, NanoSYD, Als 2, DK-6400 Sonderborg, Denmark..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Indian Inst Technol Ropar, Dept Phys, Rupnagar 140001, Punjab, India..
    Kim, Sang-Jae
    Jeju Natl Univ, Fac Appl Energy Syst, Nanomat & Syst Lab, Major Mechatron Engn, Jeju 63243, South Korea.;Jeju Natl Univ, Fac Appl Energy Syst, Nanomat & Syst Lab, Major Mech Engn, Jeju 63243, South Korea.;Jeju Natl Univ, Res Inst Energy New Ind, Jeju 63243, South Korea..
    Crystallinity modulation originates ferroelectricity like nature in piezoelectric selenium2022In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 95, article id 107008Article in journal (Refereed)
    Abstract [en]

    Modern room temperature ferroelectrics/piezoelectrics significantly impact advanced nanoelectronics than conventional chemical compounds. Changes in crystallinity modulation, long-range order of atoms in metalloids permits the design of novel materials. The ferroelectric like nature of a single element (selenium, Se) is demonstrated via in-plane (E perpendicular to(ar) to the Se helical chains in micro-rod (MR)) and out-of-plane (E parallel to(el) to the Se helical chains in MR) polarization. Atomic electron microscopy shows large stacks of covalently bound Se atoms in a c-axis orientation for tip bias voltage-dependent switchable domains with a 180 degrees phase and butterfly displacement curves. The single crystalline Se MR has a high in-plane piezoelectric coefficient of 30 pm/V relative to polycrystalline samples due to larger grains, crystal imperfections in MR, and tuned helical chains. The energy conversion of a single Se-MR demonstrated via d(13), d(12) (or d(15)) piezoelectric modes.

  • 17.
    Almeida, J
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ahuja, Rajeev
    Tuning structural, electronic and optical properties of BexZn1-xTe2006In: Applied Physics Letters, Vol. 89, p. 061913-Article in journal (Refereed)
  • 18.
    Almeida, Roseley
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Univ Fed Bahia, Inst Fis, Campus Univ Ondina, Salvador, BA, Brazil.
    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.
    Almeida, Jailton
    Univ Fed Bahia, Inst Fis, Campus Univ Ondina, BR-40210340 Salvador, BA, Brazil..
    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, Stockholm, Sweden.
    Theoretical Evidence behind Bifunctional Catalytic Activity in Pristine and Functionalized Al2C Monolayers2018In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 19, no 1, p. 148-152Article in journal (Refereed)
    Abstract [en]

    First principles electronic structure calculations based on the density functional theory (DFT) framework are performed to investigate hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) on two-dimensional Al2C monolayers. In addition to the pristine Al2C monolayer, monolayers doped with Nitrogen (N), Phosphorous (P), Boron (B), and Sulphur (S) are also investigated. After determining the individual adsorption energy of hydrogen and oxygen on the different functionalized Al2C monolayers, the adsorption free energies are predicted for each of the functionalized monolayers in order to assess their suitability for HER or OER. The density of states and optical absorption spectra calculations along with the work function of the functionalized Al2C monolayers enable us to gain a profound understanding of the electronic structure for the individual system and their relation to the water splitting mechanism.

  • 19.
    Alniss, Hasan Y.
    et al.
    Univ Sharjah, Coll Pharm, POB 27272, Sharjah, U Arab Emirates;Univ Sharjah, Sharjah Inst Med Res, POB 27272, Sharjah, U Arab Emirates.
    Witzel, Ini-Isabee
    New York Univ Abu Dhabi, Core Technol Platform, POB 129188, Abu Dhabi, U Arab Emirates.
    Semreen, Mohammad H.
    Univ Sharjah, Coll Pharm, POB 27272, Sharjah, U Arab Emirates;Univ Sharjah, Sharjah Inst Med Res, POB 27272, Sharjah, U Arab Emirates.
    Panda, Pritam Kumar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Mishra, Yogendra Kumar
    Univ Kiel, Inst Mat Sci, Funct Nanomat, Kaiserstr 2, D-24143 Kiel, Germany;Univ Southern Denmark, NanoSYD, Mads Clausen Inst, Alsion 2, DK-6400 Sonderborg, Denmark.
    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, SE-10044 Stockholm, Sweden.
    Parkinson, John A.
    Univ Strathclyde, Dept Pure & Appl Chem, WestCHEM, 295 Cathedral St, Glasgow G1 1XL, Lanark, Scotland.
    Investigation of the Factors That Dictate the Preferred Orientation of Lexitropsins in the Minor Groove of DNA2019In: Journal of Medicinal Chemistry, ISSN 0022-2623, E-ISSN 1520-4804, Vol. 62, no 22, p. 10423-10440Article in journal (Refereed)
    Abstract [en]

    Lexitropsins are small molecules that bind to the minor groove of DNA as antiparallel dimers in a specific orientation. These molecules have shown therapeutic potential in the treatment of several diseases; however, the development of these molecules to target particular genes requires revealing the factors that dictate their preferred orientation in the minor grooves, which to date have not been investigated. In this study, a distinct structure (thzC) was carefully designed as an analog of a well-characterized lexitropsin (thzA) to reveal the factors that dictate the preferred binding orientation. Comparative evaluations of the biophysical and molecular modeling results of both compounds showed that the position of the dimethylaminopropyl group and the orientation of the amide links of the ligand with respect to the 5'-3'-ends; dictate the preferred orientation of lexitropsins in the minor grooves. These findings could be useful in the design of novel lexitropsins to selectively target specific genes.

  • 20. Anikina, E. V.
    et al.
    Banerjee, A.
    KTH Royal Inst Technol, Dept Mat & Engn, Appl Mat Phys, S-10044 Stockholm, Sweden..
    Beskachko, V. P.
    South Ural State Univ, Inst Nat Sci & Math, 76 Lenin Prospekt, Chelyabinsk 454014, Russia..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Dept Mat & Engn, Appl Mat Phys, S-10044 Stockholm, Sweden..
    Influence of Kubas-type interaction of B-Ni codoped graphdiyne with hydrogen molecules on desorption temperature and storage efficiency2020In: Materials Today Energy, ISSN 2468-6069, Vol. 16, article id UNSP 100421Article in journal (Refereed)
    Abstract [en]

    We have investigated functionalized 2D carbon allotrope, graphdiyne (GDY), as a promising hydrogen storage media. Density functional theory with a range of vdW corrections was employed to study Ni decoration of pristine and boron-doped GDY and the interaction of resulting structures with molecular hydrogen. We showed that boron-doped GDY is thermally stable at 300 K, though, its synthesis requires an endothermic reaction. Also, boron doping enhances Ni binding with the graphdiyne by increasing the charge transfer from Ni to GDY. Ni doping drastically influenced hydrogen adsorption energies: they rise from similar to 70 meV per H-2 molecule on pristine GDY to a maximum of 1.29 eV per H-2 becoming too high in value for room temperature reversible applications. Boron doping improves the situations: in this case, after Ni decoration desorption temperature estimation is similar to 300-500 K. Overall, each Ni adatom on B-doped GDY can bind only one H-2 molecule within the needed energy range, which gives low hydrogen uptake (similar to 1.2 wt%). However, doping with boron led to the decrease in the value of hydrogen adsorption energy and good desorption temperature estimations, therefore, codoping of metal atoms and boron could be an effective strategy for other transition metals.

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  • 21.
    Anikina, Ekaterina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. South Ural State Univ, Inst Nat Sci & Math, 76 Lenin Prospekt, Chelyabinsk 454080, Russia..
    Banerjee, Amitava
    Royal Inst Technol KTH, Dept Mat & Engn, Appl Mat Phys, S-10044 Stockholm, Sweden..
    Beskachko, Valery
    South Ural State Univ, Inst Nat Sci & Math, 76 Lenin Prospekt, Chelyabinsk 454080, Russia..
    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..
    Li-decorated carbyne for hydrogen storage: charge induced polarization and van't Hoff hydrogen desorption temperature2020In: Sustainable Energy & Fuels, E-ISSN 2398-4902, Vol. 4, no 2, p. 691-699Article in journal (Refereed)
    Abstract [en]

    We have studied carbyne as a promising hydrogen storage material. Density functional theory simulations with vdW corrections have been used to investigate lithium sorption on carbyne and the interaction of pristine and Li-functionalized carbon chains with molecular hydrogen. We showed that Li adatoms at small concentrations stay atomically dispersed on carbyne, donating 0.9e to the chain. Moreover, in the presence of Li, hydrogen adsorption energy increases by more than 5 times in comparison with pristine carbyne. Overall, up to three hydrogen molecules per Li adatom have an adsorption energy close to the range of 200-600 meV per H-2, which is necessary for effective sorption/desorption cycles. The resulting theoretical uptake (7.1 wt%) is higher than the U.S. Department of Energy's ultimate goal (6.5 wt%). The calculated van't Hoff desorption temperatures exceed considerably the boiling point of liquid nitrogen. Our results confirm the potential of Li-decorated carbyne for hydrogen storage.

  • 22.
    Anikina, Ekaterina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. South Ural State Univ, Inst Nat Sci & Math, 76 Lenin Prospekt, Chelyabinsk 454080, Russia.
    Banerjee, Amitava
    KTH Royal Inst Technol, Dept Mat & Engn, Appl Mat Phys, S-10044 Stockholm, Sweden.
    Beskachko, Valery
    South Ural State Univ, Inst Nat Sci & Math, 76 Lenin Prospekt, Chelyabinsk 454080, Russia.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Dept Mat & Engn, Appl Mat Phys, S-10044 Stockholm, Sweden.
    Li-Functionalized Carbon Nanotubes for Hydrogen Storage: Importance of Size Effects2019In: ACS APPLIED NANO MATERIALS, ISSN 2574-0970, Vol. 2, no 5, p. 3021-3030Article in journal (Refereed)
    Abstract [en]

    We investigated Li-doped carbon nanotubes (CNTs) as a promising hydrogen storage media. In this computational model, we considered isolated lithium atom adsorbed on a CNT wall as an adsorption site for hydrogen. We focused on the influence of size effects on the structural and energetic characteristics of CNT(n,n)@Li+kH(2) complexes where n = 5, 7, 9; k = 1,..., 6; N, = 4, 5, 6 (N-c is translation length of CNT, expressed in terms of a number of CNT unit cells). We proved that modeled CNT length substantially influences internal sorption of Li and hydrogen on the narrow tube (5,5), which subsequently alters the adsorption energies of H-2 molecules and causes the deformation of the carbon framework. Moreover, the size effects are not pronounced in the case of external sorption for all considered CNT translation lengths and diameters. We have not observed any noticeable qualitative difference between internal and external hydrogen sorption in the nanotube wider than CNT(5,5). In the case of external adsorption on all considered nanotubes, doping with Li increases hydrogen adsorption energies of up to four H-2 molecules by 100 meV in comparison with pure CNTs. And the local density approximation estimations (similar to 250 meV/H-2) of adsorption energy on Li-decorated CNTs exceed the lowest requirement proposed by the U.S. Department of Energy (200 meV/H-2). In the case of internal sorption on Li-functionalized tubes, the generalized gradient approximation also gives hydrogen adsorption energies in the desired range of 200-600 meV/H-2. However, steric hindrances could prevent sufficient hydrogen uptakes (less than 2 wt % inside CNT(5,5)). We believe that our findings on the size effects are important for estimation of CNT's hydrogen storage properties.

  • 23.
    Anikina, Ekaterina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. South Ural State Univ, Inst Nat Sci & Math, 76 Lenin Prospekt, Chelyabinsk 454014, Russia..
    Hussain, Tanveer
    Univ Western Australia, Sch Mol Sci, Perth, WA 6009, Australia..
    Beskachko, Valery
    South Ural State Univ, Inst Nat Sci & Math, 76 Lenin Prospekt, Chelyabinsk 454014, Russia..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Dept Mat & Engn, Appl Mat Phys, S-10044 Stockholm, Sweden..
    Elucidating hydrogen storage properties of two-dimensional siligraphene (SiC8) monolayers upon selected metal decoration2020In: Sustainable Energy & Fuels, E-ISSN 2398-4902, Vol. 4, no 11, p. 5578-5587Article in journal (Refereed)
    Abstract [en]

    Density functional theory calculations with dispersion corrections were employed to investigate the hydrogen (H-2) adsorptive properties of siligraphene (SiC8), pristine and decorated with selected alkali (Li, Na, and K) and alkaline-earth (Be, Mg, and Ca) metals. We found that all the considered metals (Me), except Mg and Be, bind strongly to SiC8 even at high doping concentrations (SiC8Me2) by donating a major portion of their valence electrons to SiC8. Ab initio molecular dynamics (AIMD) simulations confirmed the thermal stabilities of SiC8Me2 (Me = Li, Na, K, Ca) at 300 K. We showed that Li, Na, and Ca-doped SiC8 adsorbed multiple H-2 molecules with binding energies (E-bind) at least two times stronger than that of the pristine SiC8 (Epristinebind = -70 meV per H-2). Overall, both SiC8Li2 and SiC8Ca2 adsorbed two and four H-2 molecules per metal adatom, respectively, having E-bind within the desirable range for an effective adsorption/desorption process. The resulting gravimetric densities of SiC8Li2 and SiC8Ca2 were 5.5 wt% and 7.3 wt%, respectively, surpassing the U.S. Department of Energy's 2025 goal of 5.5 wt%. The estimated H-2 desorption temperatures exceed substantially the boiling point of liquid nitrogen, confirming the potential of light metal decorated SiC8 as a promising material for H-2 storage.

  • 24.
    Anikina, Ekaterina
    et al.
    South Ural State Univ, Inst Nat Sci & Math, Chelyabinsk 454014, Russia.;Uppsala Univ, Dept Phys & Astron, Mat Theory Div, S-75120 Uppsala, Sweden..
    Hussain, Tanveer
    Univ Western Australia, Sch Mol Sci, Perth, WA 6009, Australia..
    Beskachko, Valery
    South Ural State Univ, Inst Nat Sci & Math, Chelyabinsk 454014, Russia..
    Bae, Hyeonhu
    Konkuk Univ, Dept Phys, Seoul 05029, South Korea..
    Lee, Hoonkyung
    Konkuk Univ, Dept Phys, Seoul 05029, South Korea..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Uppsala UniKTH Royal Inst Technol, Appl Mat Phys, Dept Mat & Engn, S-10044 Stockholm, Sweden..
    Tunning Hydrogen Storage Properties of Carbon Ene-Yne Nanosheets through Selected Foreign Metal Functionalization2020In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 124, no 31, p. 16827-16837Article in journal (Refereed)
    Abstract [en]

    In this study, we have employed density functional theory with a range of van der Waals corrections to study geometries, electronic structures, and hydrogen (H-2) storage properties of carbon ene-yne (CEY) decorated with selected alkali (Na, K) and alkaline-earth metals (Mg, Ca). We found that all metals, except Mg, bind strongly by donating a major portion of their valence electrons to the CEY monolayers. Thermal stabilities of representative systems, Ca-decorated CEY monolayers, have been confirmed through ab initio molecular dynamics simulations (AIMD). We showed that each metal cation adsorbs multiple H-2 with binding energies (E-bind) considerably stronger than on pristine CEY. Among various metal dopants, Ca stands out with the adsorption of five H-2 per each Ca having E-bind values within the desirable range for effective adsorption/desorption process. The resulting gravimetric density for CEY@Ca has been found around 6.0 wt % (DFT-D3) and 8.0 wt % (LDA), surpassing the U.S. Department of Energy's 2025 goal of 5.5 wt %. The estimated H-2 desorption temperature in CEY@Ca exceeds substantially the boiling point of liquid nitrogen, which confirms its potential as a practical H-2 storage medium. We have also employed thermodynamic analysis to explore the H-2 adsorption/desorption mechanism at varied conditions of temperature and pressure for real-world applications.

  • 25.
    Anikina, Ekaterina
    et al.
    South Ural State Univ, Inst Nat Sci & Math, Chelyabinsk 454080, Russia..
    Naqvi, S. Rabab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bae, Hyeonhu
    Konkuk Univ, Dept Phys, Seoul 05029, South Korea..
    Lee, Hoonkyung
    Konkuk Univ, Dept Phys, Seoul 05029, South Korea..
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. 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. Indian Inst Technol Ropar, Dept Phys, Rupnagar 140001, Punjab, India..
    Hussain, Tanveer
    Univ Queensland, Sch Chem Engn, Brisbane, Qld 4072, Australia.;Univ New England, Sch Sci & Technol, Armidale, NSW 2351, Australia..
    High-capacity reversible hydrogen storage properties of metal-decorated nitrogenated holey graphenes2022In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 47, no 19, p. 10654-10664Article in journal (Refereed)
    Abstract [en]

    Motivated by the need for an effective way of storing hydrogen (H-2), a promising energy carrier, we have performed density functional theory (DFT) calculations with different van der Waals corrections coupled with the statistical thermodynamic analysis and ab initio molecular dynamics (AIMD) on the light-metal decorated nitrogenated holey graphene (C2N) monolayers. We have found that the decoration by selected light metals (Na, Mg, Ca) improves the H2 adsorption on the C2N to the desired levels (> 150 meV/H-2). Moreover, the metal dopants strongly bonded with C2N even at higher doping concentrations, which invalidates the metal clusters formation. Among considered metals, Na and Mg resulted in H-2 storage capacities of 5.5 and 6.9 wt%, respectively, which exceed the target set by the U.S. Department of Energy's for 2025. Thermodynamic analysis and the AIMD simulations were employed to investigate the H-2 sorption at varied conditions of temperature and pressure for practical applications.

  • 26.
    Anversa, Jonas
    et al.
    Univ Fed Santa Maria, Dept Fis, BR-97105900 Santa Maria, RS, Brazil.;Fac Meridional, Escola Engn Civil, BR-99070220 Passo Fundo, RS, Brazil..
    Chakraborty, Sudip
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Piquini, Paulo
    Univ Fed Santa Maria, Dept Fis, BR-97105900 Santa Maria, RS, Brazil..
    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..
    High pressure driven superconducting critical temperature tuning in Sb2Se3 topological insulator2016In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 108, no 21, article id 212601Article in journal (Refereed)
    Abstract [en]

    In this letter, we are reporting the change of superconducting critical temperature in Sb2Se3 topological insulator under the influence of an external hydrostatic pressure based on first principles electronic structure calculations coupled with Migdal-Eliashberg model. Experimentally, it was shown previously that Sb2Se3 was undergoing through a transition to a superconducting phase when subjected to a compressive pressure. Our results show that the critical temperature increases up to 6.15K under the pressure unto 40GPa and, subsequently, drops down until 70 GPa. Throughout this pressure range, the system is preserving the initial Pnma symmetry without any structural transformation. Our results suggest that the possible relevant mechanism behind the superconductivity in Sb2Se3 is primarily the electron-phonon coupling. Published by AIP Publishing.

  • 27.
    Arapan, Sergiu
    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.
    High-pressure phase transformations in carbonates2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, no 18, p. 184115-Article in journal (Refereed)
    Abstract [en]

    High-pressure phase transitions sequences in CaCO3, SrCO3, and BaCO3 are studied by first-principle electronic structure calculations. Each of the carbonates undergoes the aragonite to postaragonite phase transition with pressure in agreement with the experimental observation of Ono et al. However, the postaragonite to post-postaragonite phase transition, predicted by Oganov et al. and later observed in CaCO3, is unlikely to occur in SrCO3 and BaCO3. Hence, the concept that isostructural compounds will exhibit the same type of pressure-induced phase transitions has limitations. A change of the hybridization of the carbon atom from sp(2) to sp(3) within the Pmcn phase occurs in each of compounds, thus the carbonates are likely to transform at very high pressure to structures with tetrahedral CO4-4 carbonate group.

  • 28.
    Arapan, Sergiu
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    De Almeida, Jailton Souza
    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.
    Formation of sp(3) hybridized bonds and stability of CaCO3 at very high pressure2007In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 98, no 26, p. 268501-Article in journal (Refereed)
    Abstract [en]

    By performing ab initio electronic structure calculations, we observed a new high-pressure phase transition within the Pmcn structure of CaCO3. This transition is characterized by the change of the carbon's sp hybridization state and is driven by the intrinsic property of the carbon atom to form tetrahedral covalent bonds at high pressure. The formation of sp(3) hybridized bonds explains the stability of MgCO3 and CaCO3 at Earth's lower mantle pressure conditions and may serve as a criterion for searching new possible high-pressure phases of carbon bearing minerals.

  • 29.
    Arapan, Sergiu
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Mao, Ho-kwang
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Prediction of incommensurate crystal structure in Ca at high pressure2008In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 105, no 52, p. 20627-20630Article in journal (Refereed)
    Abstract [en]

    Ca shows an interesting high-pressure phase transformation sequence, but, despite similar physical properties at high pressure and affinity in the electronic structure with its neighbors in the periodic table, no complex phase has been identified for Ca so far. We predict an incommensurate high-pressure phase of Ca from first principle calculations and describe a procedure of estimating incommensurate structure parameters by means of electronic structure calculations for periodic crystals. Thus, by using the ab initio technique for periodic structures, one can get not only reliable information about the electronic structure and structural parameters of an incommensurate phase, but also identify and predict such phases in new elements.

  • 30.
    Arapan, Sergiu
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Skorodumova, Natalia V.
    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.
    Determination of the Structural Parameters of an Incommensurate Phase from First Principles: The Case of Sc-II2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 102, no 8, p. 085701-Article in journal (Refereed)
    Abstract [en]

    We propose a procedure to accurately describe the structural parameters of an incommensurate phase using ab initio methods by approximating it with a set of analogous commensurate supercells. We apply this approach to obtain the structural parameters of the Sc-II phase, which has recently been identified as a complex incommensurate structure similar to Sr-V. The calculated incommensurate ratio gamma, lattice parameters, and Wyckoff positions of Sc-II are in excellent agreement with the available experimental data. Our results show that gamma increases with pressure up to 60 GPa approaching but never reaching the commensurate value 4/3. Hence calculations do not confirm the prediction made based on the reanalyzing of experimental data. When pressure exceeds 70 GPa, gamma shows a sharp decrease that might be considered as the precursor of a new structural phase transition.

  • 31.
    Araujo, C. Moyses
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Kapilashrami, Mukes
    Jun, Xu
    Jayakumar, O. D.
    Nagar, Sandeep
    Wu, Yan
    Århammar, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Belova, Lyubov
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Gehring, Gillian A.
    Rao, K. V.
    Room temperature ferromagnetism in pristine MgO thin films2010In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 96, no 23, p. 232505-Article in journal (Refereed)
    Abstract [en]

    Robust ferromagnetic ordering at, and well above room temperature is observed in pure transparent MgO thin films (<170 nm thick) deposited by three different techniques. Careful study of the wide scan x-ray photoelectron spectroscopy rule out the possible presence of any magnetic contaminants. In the magnetron sputtered films, we observe magnetic phase transitions as a function of film thickness. The maximum saturation magnetization of 5.7 emu/cm(3) is measured on a 170 nm thick film. The films above 500 nm are found to be diamagnetic. Ab initio calculations suggest that the ferromagnetism is mediated by cation vacancies.

  • 32.
    Araujo, Carlos Moyses
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Ahuja, Rajeev
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Electronic and optical properties of pressure induced phases of MgH22005In: Journal of Alloys and Compounds, ISSN 0925-8388, Vol. 404, no 16, p. 220-Article in journal (Refereed)
    Abstract [en]

    The electronic and optical properties of pressure-induced phases of MgH2 are investigated using the full-potential linearized augmented plane wave method. The absorption features are investigated by means of the calculated complex dielectric function and the analysis are made based on the electronic structure. The phases as a whole exhibit a color neutral insulator behavior. The calculated band gap are in good agreement with earlier theoretical investigations. The absorption edges corrected by scissor operation matched quite well the experimental findings. The optical anisotropy has also been evaluated.

  • 33.
    Araujo, Carlos Moyses
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Ahuja, Rajeev
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Osorio Guillén, J. M.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Jena, Puru
    Role of Titanium in Hydrogen Desorption in Crystalline Sodium Alanate2005In: Applied Physics Letters, ISSN 0003-6951, Vol. 86, no 25, p. 251913-Article in journal (Refereed)
    Abstract [en]

    The role of Ti in improving the thermodynamics of hydrogen desorption in crystalline sodium alanate (NaAlH4) has been investigated by using the density functional theory. The total energy calculations reveal that Ti prefers to occupy the Na site over that of the Al site when the atomic energies are used as the reference. However, the use of the cohesive energies of Al, Na, and Ti leads to the Al site being the least unfavourable site. Irrespective of whether Ti occupies the Na or the Al site, the energy necessary to remove a hydrogen atom from Ti substituted sodium alanate is significantly lowered from that of the pure alanate. The understanding gained here may help in designing hydrogen storage materials suitable for industrial applications.

  • 34.
    Araujo, Carlos Moyses
    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.
    Osorio Guillén, Jorge Mario
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Jena, P
    Role of titanium in hydrogen desorption in crystalline sodium alanate2005In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 86, no 25, article id 251913Article in journal (Refereed)
    Abstract [en]

    The role of Ti in improving the thermodynamics of hydrogen desorption in crystalline sodium alanate (NaAlH4) has been investigated by using the density functional theory. The total energy calculations reveal that Ti prefers to occupy the Na site over that of the Al site when the atomic energies are used as the reference. However, the use of the cohesive energies of Al, Na, and Ti leads to the Al site being the least unfavourable site. Irrespective of whether Ti occupies the Na or the Al site, the energy necessary to remove a hydrogen atom from Ti substituted sodium alanate is significantly lowered from that of the pure alanate. The understanding gained here may help in designing hydrogen storage materials suitable for industrial applications.

  • 35.
    Araujo, Carlos Moyses
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Ahuja, Rajeev
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Talyzin, A. V.
    Sundqvist, B.
    Pressure-induced structural phase transition in NaBH42005In: Physical Review B, ISSN 1198-0121, Vol. 72, no 5, p. 054125-Article in journal (Refereed)
    Abstract [en]

    We present a combined experimental and theoretical study of the technologically important NaBH4 compound under high pressure. Using Raman spectroscopy at room temperature, we have found that NaBH4 undergoes a structural phase transformation starting at 10.0 GPa with the pure high pressure phase being established above 15.0 GPa. In order to compare the Raman data recorded under high pressure with the low temperature tetragonal phase of NaBH4, we have also performed a cooling experiment. The known order-disorder transition from the fcc to the tetragonal structure was then observed. However, the new high pressure phase does not correspond to this low temperature structure. Using first principle calculations based on the density functional theory, we show that the new high pressure phase corresponds to the α-LiAlH4 type structure. We have found a good agreement between the measured and calculated transition pressures. Additionally, we present the electronic structure of both the fcc and the high pressure phases.

  • 36.
    Araujo, Carlos Moyses
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Lebègue, Sebastien
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Eriksson, Olle
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Arnaud, B.
    Alouani, M.
    Ahuja, Rajeev
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Electronic and optical properties of MgH2: a first-principle GW investigation2005In: Journal of Applied Physics, ISSN 0021-8979, Vol. 98, no 9, p. 096106-Article in journal (Refereed)
    Abstract [en]

    The electronic structure of MgH2 is studied using the state of the art all-electron projector-augmented-wave GW approximation. Both the ground-state and the high-pressure transformations are considered in this investigation. We have found an indirect (direct) band-gap of 5.58 eV (6.52 eV) for α-MgH2, which has a good agreement with the experimental findings. For the γ- and β-phases, we have found indirect (direct) band-gap values of 5.24 eV (5.33 eV) and 3.90 eV (4.72 eV), respectively. The optical properties are investigated by means of the complex dielectric function, which is calculated within the framework of a full-potential linearized augmented plane wave method and corrected by scissor operators. All phases are found to be color neutral insulators.

  • 37.
    Araujo, Carlos Moyses
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Li, Sa
    Ahuja, Rajeev
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Jena, Puru
    Vacancy Mediated Hydrogen Desorption in NaAlH42005In: Physical Review B, ISSN 1098-0121, Vol. 72, no 16, p. 165101-Article in journal (Refereed)
    Abstract [en]

    First principles calculations based on density functional theory are carried out to understand the mechanisms responsible for hydrogen desorption from Ti doped sodium-alanate (NaAlH4). While the energy needed to remove a hydrogen atom from NaAlH4 with Ti substituted either at the Na site or at Al site is found to be significantly lower than that from the pristine NaAlH4, the presence of Na-vacancies is shown to play an even larger role: It is not only an order of magnitude smaller than that from Ti doped sodium alanate, but the removal of hydrogen associated with a Na-vacancy is exothermic with respect to formation of H2 molecule. Furthermore, we show that the unusual stabilization of the magic AlH3 cluster in the vacancy containing sodium-alanate is responsible for this diminished value of hydrogen removal energy. It is suggested that this role of vacancy can be exploited in the design and synthesis of complex light metal hydrides suitable for hydrogen storage.

  • 38.
    Araujo, Carlos Moyses
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Nagar, Sandeep
    Ramzan, Muhammad
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Shukla, R.
    Jayakumar, O. D.
    Tyagi, A. K.
    Liu, Yi-Sheng
    Chen, Jeng-Lung
    Glans, Per-Anders
    Chang, Chinglin
    Blomqvist, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Lizárraga, Raquel
    Holmstrom, Erik
    Belova, Lyubov
    Guo, Jinghua
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Applied Materials Physics, Department of Materials and Engineering, Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden.
    Rao, K. V.
    Disorder-induced Room Temperature Ferromagnetism in Glassy Chromites2014In: Scientific Reports, E-ISSN 2045-2322, Vol. 4, p. 4686-Article in journal (Refereed)
    Abstract [en]

    We report an unusual robust ferromagnetic order above room temperature upon amorphization of perovskite [YCrO3] in pulsed laser deposited thin films. This is contrary to the usual expected formation of a spin glass magnetic state in the resulting disordered structure. To understand the underlying physics of this phenomenon, we combine advanced spectroscopic techniques and first-principles calculations. We find that the observed order-disorder transformation is accompanied by an insulator-metal transition arising from a wide distribution of Cr-O-Cr bond angles and the consequent metallization through free carriers. Similar results also found in YbCrO3-films suggest that the observed phenomenon is more general and should, in principle, apply to a wider range of oxide systems. The ability to tailor ferromagnetic order above room temperature in oxide materials opens up many possibilities for novel technological applications of this counter intuitive effect.

  • 39.
    Araujo, Moyses
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Blomqvist, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Scheicher, Ralph H.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Chen, Ping
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Superionicity in the hydrogen storage material Li2NH: Molecular dynamics simulations2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 17, p. 172101-Article in journal (Refereed)
    Abstract [en]

    We have employed ab initio molecular dynamics simulations in an attempt to study a temperature-induced order-disorder structural phase transformation that occurs in Li2NH at about 385 K. A structural phase transition was observed by us in the temperature range 300-400 K, in good agreement with experiment. This transition is associated with a melting of the cation sublattice (Li+), giving rise to a superionic phase, which in turn is accompanied by an order-disorder transition of the N-H bond orientation. The results obtained here can contribute to a better understanding of the hydrogen storage reactions involving Li2NH and furthermore broaden its possible technological applications toward batteries and fuel cells.

  • 40.
    Araujo, Rafael B.
    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. Royal Inst Technol KTH, Appl Mat Phys, Dept Mat & Engn, S-10044 Stockholm, Sweden..
    Evaluating bulk Nb2O2F3 for Li-battery electrode applications2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 5, p. 3530-3535Article in journal (Refereed)
    Abstract [en]

    This investigation has the primary objective of elucidating the lithium intercalation process in the crystal structure of a new niobium oxyfluoride compound Nb2O2F3. The framework of the density functional theory was applied in a generalized gradient approximation together with the hybrid functional method. It is revealed that lithium atoms intercalate in this material in a maximum concentration of one Li atom per formula unit forming LiNb2O2F3. Moreover, octahedral positions in between the layers of Nb-O-F appear as the Li preferred occupancy resulting in a structural volume expansion of only 5%. Electronic structure evolution with the insertion of lithium displays a transformation from semi-conductor to metal when half of the lithium atoms are added. This transformation occurs due to a symmetry break induced by the transition from the + 8 to + 7 oxidation state of half of the Nb2 dimers. Then, after full lithiation the symmetry is recovered and the material becomes a semiconductor again with a band gap amounting to 1 eV. The evaluated average deintercalation potential reaches 1.29 V vs. Li/Li+ with activation energy for lithium ion migration of 0.79 eV. The computed low potential of the redox reaction Nb-2(8+) to Nb-2(7+) includes niobium oxyfluoride in the map of possible materials for the anode application of Li-ion batteries.

  • 41.
    Araujo, Rafael B.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Banerjee, Amitava
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Panigrahi, Puspamitra
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Hindustan Univ, Ctr Clean Energy & Nanoconvergence, Madras, Tamil Nadu, India.
    Yang, Li
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Sjödin, Martin
    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.
    Araujo, C. Moyses
    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, Appl Mat Phys, S-10044 Stockholm, Sweden.; Royal Inst Technol KTH, Dept Engn, S-10044 Stockholm, Sweden.
    Assessing Electrochemical Properties of Polypyridine and Polythiophene for Prospective Application in Sustainable Organic Batteries2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 4, p. 3307-3314Article in journal (Refereed)
    Abstract [en]

    Conducting polymers are being considered promising candidates for sustainable organic batteries mainly due to their fast electron transport properties and high recyclability. In this work, key properties of polythiophene and polypyridine have been assessed through a combined theoretical and experimental study focusing on such applications. A theoretical protocol has been developed to calculate redox potentials in solution within the framework of the density functional theory and using continuous solvation models. Here, the evolution of the electrochemical properties of solvated oligomers as a function of the length of the chain is analyzed and then the polymer properties are estimated via linear regressions using ordinary least square. The predicted values were verified against our electrochemical experiments. This protocol can now be employed to screen a large database of compounds in order to identify organic electrodes with superior properties.

  • 42.
    Araujo, Rafael B.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Banerjee, Amitava
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Panigrahi, Puspamitra
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Hindustan Univ, Ctr Clean Energy & Nanoconvergence, Chennai, Tamil Nadu, India.
    Yang, Li
    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.
    Sjödin, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Araujo, C. Moyses
    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.
    Designing strategies to tune reduction potential of organic molecules for sustainable high capacity batteries application2017In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 5, no 9, p. 4430-4454Article in journal (Refereed)
    Abstract [en]

    Organic compounds evolve as a promising alternative to the currently used inorganic materials in rechargeable batteries due to their low-cost, environmentally friendliness and flexibility. One of the strategies to reach acceptable energy densities and to deal with the high solubility of known organic compounds is to combine small redox active molecules, acting as capacity carrying centres, with conducting polymers. Following this strategy, it is important to achieve redox matching between the chosen molecule and the polymer backbone. Here, a synergetic approach combining theory and experiment has been employed to investigate this strategy. The framework of density functional theory connected with the reaction field method has been applied to predict the formal potential of 137 molecules and identify promising candidates for the referent application. The effects of including different ring types, e.g. fused rings or bonded rings, heteroatoms, [small pi] bonds, as well as carboxyl groups on the formal potential, has been rationalized. Finally, we have identified a number of molecules with acceptable theoretical capacities that show redox matching with thiophene-based conducting polymers which, hence, are suggested as pendent groups for the development of conducting redox polymer based electrode materials.

  • 43.
    Araujo, Rafael B.
    et al.
    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.
    Unveiling the charge migration mechanism in Na2O2: implications for sodium-air batteries2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 12, p. 8203-8209Article in journal (Refereed)
    Abstract [en]

    Metal-air batteries have become promising candidates for modern energy storage due to their high theoretical energy density in comparison to other storage devices. The lower overpotential of Na compared with Li makes Na-air batteries more efficient in terms of battery lifetime. Additionally, the abundance of Na over Li is another advantage for Na batteries compared to Li batteries. Na2O2 is one of the main products of sodium-air battery reactions. The efficiency of air cells is always related to the charge transport mechanisms in the formed product. To unveil these diffusion mechanisms in one of the main products of the cell reaction Na-O-2 we systematically investigate the mobility of charge carriers as well as the electronic structural properties of sodium peroxide. The framework of the density functional theory based on hybrid functional approach is used to study the mobility of charge carriers and intrinsic defects in Na2O2. Our calculations reveal that the formation of small electron and hole polarons is preferentially occurring over the delocalized state in the crystal structure of Na2O2. The migration of these small polarons displays activation energies of about 0.92 eV and 0.32 eV for the electron and hole polarons respectively, while the analysis of the charged sodium vacancy mobility reveals an activation energy of about 0.5 eV. These results suggest that the charge transport in sodium peroxide would mainly occur through the diffusion of hole polarons.

  • 44.
    Araujo, Rafael B.
    et al.
    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.
    Barpanda, Prabeer
    Indian Inst Sci, Faraday Mat Lab, Mat Res Ctr, 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. Royal Inst Technol KTH, Appl Mat Phys, Dept Mat & Engn, S-10044 Stockholm, Sweden..
    Na2M2(SO4)(3) (M = Fe, Mn, Co and Ni): towards high-voltage sodium battery applications2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 14, p. 9658-9665Article in journal (Refereed)
    Abstract [en]

    Sodium-ion-based batteries have evolved as excellent alternatives to their lithium-ion-based counterparts due to the abundance, uniform geographical distribution and low price of Na resources. In the pursuit of sodium chemistry, recently the alluaudite framework Na2M2(SO4)(3) has been unveiled as a high-voltage sodium insertion system. In this context, the framework of density functional theory has been applied to systematically investigate the crystal structure evolution, density of states and charge transfer with sodium ions insertion, and the corresponding average redox potential, for Na2M2(SO4)(3) (M = Fe, Mn, Co and Ni). It is shown that full removal of sodium atoms from the Fe-based device is not a favorable process due to the 8% volume shrinkage. The imaginary frequencies obtained in the phonon dispersion also reflect this instability and the possible phase transition. This high volume change has not been observed in the cases of the Co- and Ni-based compounds. This is because the redox reaction assumes a different mechanism for each of the compounds investigated. For the polyanion with Fe, the removal of sodium ions induces a charge reorganization at the Fe centers. For the Mn case, the redox process induces a charge reorganization of the Mn centers with a small participation of the oxygen atoms. The Co and Ni compounds present a distinct trend with the redox reaction occurring with a strong participation of the oxygen sublattice, resulting in a very small volume change upon desodiation. Moreover, the average deintercalation potential for each of the compounds has been computed. The implications of our findings have been discussed both from the scientific perspective and in terms of technological aspects.

  • 45.
    Araujo, Rafael B.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    de Almeida, J. S.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    da Silva, A. Ferreira
    Univ Fed Bahia, Inst Fis, Salvador, BA, Brazil..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Insights in the electronic structure and redox reaction energy in LiFePO4 battery material from an accurate Tran-Blaha modified Becke Johnson potential2015In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 118, no 12, article id 125107Article in journal (Refereed)
    Abstract [en]

    The main goals of this paper are to investigate the accuracy of the Tran-Blaha modified Becke Johnson (TB-mBJ) potential to predict the electronic structure of lithium iron phosphate and the related redox reaction energy with the lithium deintercalation process. The computed electronic structures show that the TB-mBJ method is able to partially localize Fe-3d electrons in LiFePO4 and FePO4 which usually is a problem for the generalized gradient approximation (GGA) due to the self interaction error. The energy band gap is also improved by the TB-mBJ calculations in comparison with the GGA results. It turned out, however, that the redox reaction energy evaluated by the TB-mBJ technique is not in good agreement with the measured one. It is speculated that this disagreement in the computed redox energy and the experimental value is due to the lack of a formal expression to evaluate the exchange and correlation energy. Therefore, the TB-mBJ is an efficient method to improve the prediction of the electronic structures coming form the standard GGA functional in LiFePO4 and FePO4. However, it does not appear to have the same efficiency for evaluating the redox reaction energies for the investigated system.

  • 46.
    Araujo, Rafael B.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Islam, Muhammed Shafiqul
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Natl Univ Bangladesh, DSHE, Dhaka 1000, Bangladesh..
    Chakraborty, Sudip
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, R.
    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..
    Predicting electrochemical properties and ionic diffusion in Na2+2xMn2-x(SO4)(3): crafting a promising high voltage cathode material2016In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 4, no 2, p. 451-457Article in journal (Refereed)
    Abstract [en]

    Sodium ion batteries have emerged as a good alternative to lithium based systems due to their low cost of production. In this scenario, the search for higher voltage, sodium cathodes results in a new promising alluaudite structure Na2+2xMn2-x(SO4)(3). The structural, electronic and Na diffusion properties along with defects have been reported in this investigation within the framework of density functional theory. A band gap of 3.61 eV has been computed and the average deintercalation potential is determined to be 4.11 V vs. Na/Na+. A low concentration of anti-site defects is predicted due to their high formation energy. The biggest issue for the ionic diffusion in the Na2+2xMn2-x(SO4)(3) crystal structure is revealed to be the effect of Mn vacancies increasing the activation energy of Na+ ions that hop along the [001] equilibrium positions. This effect leads to activation energies of almost the same high values for the ionic hop through the [010] direction characterizing a 2D like ionic diffusion mechanism in this system.

  • 47.
    Araujo, Rafael B.
    et al.
    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.
    de Almeida, J. S.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ferreira da Silva, A.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Lithium transport investigation in LixFeSiO4: A promising cathode material2013In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 173, p. 9-13Article in journal (Refereed)
    Abstract [en]

    In this paper we investigate lithium mobility in both Li2FeSiO4 and its   half-lithiated state LiFeSiO4 considering an orthorhombic crystal   structure. We find that the calculated activation energy of Li+ ions   hopping between adjacent equilibrium sites predicts two least hindered   diffusion pathways in both materials. One of them is along the [100]   direction characterizing an ionic diffusion in a straight line and the   other follows a zig-zag way between the Fe-Si-O layers. We also show   that diffusion of Li+ ions in the half-lithiated structure follows the   same behavior as in the lithiated structure. As a whole, the activation   energies for the investigated compounds present a greater value compared   with the activation energies in currently used materials such as   LiFePO4. The results were calculated in the framework of density   functional theory in conjunction with the climbing image nudged elastic   band method. The Hubbard term was added to the Kohn-Sham Hamiltonian to   overcome the delocalization problem of d electrons. Furthermore, the   diffusion coefficients were calculated for both structures considering   temperatures ranging from 300 to 700 K. (C) 2013 Elsevier Ltd. All   rights reserved.

  • 48.
    Araujo, Rafael Barros Neves
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Chakraborty, Sudip
    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.
    Unveiling the charge migration mechanism in Na2O2 : implications for sodium air batteries2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084Article in journal (Other academic)
  • 49.
    Araujo, Rafael Barros Neves de Araujo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Banerjee, Amitava
    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.
    Divulging the Hidden Capacity and Sodiation Kinetics of NaxC6Cl4O2 : A High Voltage Organic2017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455Article in journal (Other academic)
  • 50.
    Araujo, Rafael Barros Neves de
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Banerjee, Amitava
    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..
    Divulging the Hidden Capacity and Sodiation Kinetics of NaxC6Cl4O2: A High Voltage Organic Cathode for Sodium Rechargeable Batteries2017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 26, p. 14027-14036Article in journal (Refereed)
    Abstract [en]

    In the current emerging sustainable organic battery field, quinones are seen as one of the prime candidates for application in rechargeable battery electrodes. Recently, C6Cl4O2, a modified quinone, has been proposed as a high voltage organic cathode. However, the sodium insertion mechanism behind the cell reaction remained unclear due to the nescience of the right crystal structure. Here, the framework of the density functional theory (DFT) together with an evolutionary algorithm was employed to elucidate the crystal structures of the compounds NaxC6Cl4O2 (x = 0.5, 1.0, 1.5 and 2). Along with the usefulness of PBE functional to reflect the experimental potential, also the importance of the hybrid functional to divulge the hidden theoretical capacity is evaluated. We showed that the experimentally observed lower specific capacity is a result of the great stabilization of the intermediate phase Na1.5C6Cl4O2. The calculated activation barriers for the ionic hops are 0.68, 0.40, and 0.31 eV, respectively, for NaC6Cl4O2, Na1.5C6Cl4O2, and Na2C6Cl4O2. These results indicate that the kinetic process must not be a limiting factor upon Na insertion. Finally, the correct prediction of the specific capacity has confirmed that the theoretical strategy used, employing evolutionary simulations together with the hybrid functional framework, can rightly model the thermodynamic process in organic electrode compounds.

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