SwePub - search: WFRF:(Ahuja Rajeev)

Enumeration	Reference	Cover	Find
1.	Ahuja, B. L., et al. (author) A study of electron momentum density and charge transfer in W-Cu system 2009 In: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 467:1-2, s. 595-599 Journal article (peer-reviewed)abstract 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.
2.	Murugesan, Chinnasamy, et al. (author) Cobalt tetraphosphate as an efficient bifunctional electrocatalyst for hybrid sodium-air batteries 2021 In: Nano Energy. - : Elsevier BV. - 2211-2855 .- 2211-3282. ; 89 Journal article (peer-reviewed)abstract Economic and efficient bifunctional electrocatalysts are pivotal in realization of rechargeable (hybrid) metal-air batteries. It is ideal to employ noble-metal free bifunctional electrocatalysts that are not selective towards oxygen evolution and reduction (OER and ORR) activities. This work unveils cobalt-based tetraphosphate K2Co(PO3)(4) as an economic bifunctional electrocatalyst acting as cathode for rechargeable hybrid sodium-air batteries. Auto combustion route led to the development of homogeneous, carbon-coated, spherical K2Co(PO3)(4) nanoparticles enabling active site exposure to incoming guest molecules (O-2, OH-). This monoclinic compound exhibited superior oxygen evolution activity with low overpotential (ca. 0.32 V) surpassing the commercial RuO2 catalyst. Tetraphosphate K2Co(PO3)(4) was successfully implemented in hybrid Na-air batteries delivering reversible cycling with roundtrip efficiency over 70%. DFT study revealed this catalytic activity stem from the most active and stable surface (001) and half-metallic nature of Co in K2Co(PO3)(4). Cobalt tetraphosphates can be harnessed to design low cost electrocatalysts for hybrid sodium-air batteries.
3.	Abdel-Hafiez, Mahmoud, et al. (author) Pressure-induced reentrant transition in NbS3 phases : Combined Raman scattering and x-ray diffraction study 2019 In: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 99:23 Journal article (peer-reviewed)abstract 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.
4.	Adit Maark, T., et al. (author) Structural, electronic and thermodynamic properties of Al- and Si-doped α-, γ-, and β-MgH2 : Density functional and hybrid density functional calculations 2012 In: International journal of hydrogen energy. - : Elsevier BV. - 0360-3199 .- 1879-3487. ; 37:11, s. 9112-9122 Journal article (peer-reviewed)abstract In this work, we present a detailed study of Al- and Si-doped α-, γ-, and β-MgH 2 phases using the gradient corrected density functional GGA-PBE and the hybrid Hartree-Fock density functionals PBE0 and HSE06 within the framework of generalized Kohn-Sham density functional theory (DFT) using a plane-wave basis set. We investigate the structural, electronic, and thermodynamical properties of these compounds with regard to their hydrogen storage effectiveness. PBE0 and HSE06 predict cell parameters and bond lengths that are in good agreement with the GGA-PBE calculations and previously known experimental results. As expected smaller band gaps (E gs) are predicted by GGA-PBE for the pure magnesium hydride phases. PBE0 overcomes the deficiencies of DFT in treating these materials better than HSE06 and yields E gs that compare even better with previous GW calculations. Both the hybrid functionals increase the E gs of the Al-doped magnesium hydrides by much less magnitudes than of the Si-doped phases. This difference is interpreted in terms of charge density distributions. Best H 2 adsorption energies (ΔH ads) are computed by HSE06 while GGA-PBE significantly overestimates them. Si-doped α- and β-MgH 2 exhibited the least negative ΔH ads in close proximity to the H 2 binding energy range of -0.21 to -0.41 eV ideal for practical H 2 storage transportation applications.
5.	Agåker, Marcus, et al. (author) Resonant inelastic soft x-ray scattering at double core excitations in solid LiCl 2006 In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 73:24 Journal article (peer-reviewed)abstract 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.
6.	Agåker, Marcus, et al. (author) Resonant Inelastic Soft X-ray Scattering at Hollow Lithium States in Solid LiCl 2004 In: Physical Review Letters. ; 93 Journal article (peer-reviewed)
7.	Ahmadivand, Arash, et al. (author) Terahertz plasmonics : The rise of toroidal metadevices towards immunobiosensings 2020 In: Materials Today. - : ELSEVIER SCI LTD. - 1369-7021 .- 1873-4103. ; 32, s. 108-130 Research review (peer-reviewed)abstract 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.
8.	Ahmadivand, Arash, et al. (author) Toroidal Metaphotonics and Metadevices 2020 In: Laser & Photonics reviews. - : WILEY-V C H VERLAG GMBH. - 1863-8880 .- 1863-8899. ; 14:11 Research review (peer-reviewed)abstract 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.
9.	Ahuja, Rajeev, et al. (author) Ab initio investigation on the phase stability of Ti3SiC2, Ti3Si0.5Ge0.5C2 and 2006 In: High Pressure Research. ; 26, s. 127- Journal article (peer-reviewed)
10.	Ahuja, Rajeev, et al. (author) Electronic and optical properties of gamma-Al2O3 from ab initio theory 2004 In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 16:16, s. 2891-2900 Journal article (peer-reviewed)abstract We report on a density functional theory calculation of the electronic structure and optical properties of gamma-Al2O3. We have made a comparison between the optical and electronic properties of the alpha and gamma phases of alumina. The calculated bulk modulus of the gamma phase is slightly lower than that of the a phase. The calculated static dielectric function and the optical constant of the gamma phase are very close to those of the alpha phase.
11.	Ahuja, Rajeev, et al. (author) Electronic and optical properties of lead iodide 2002 In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 92:12, s. 7219-7224 Journal article (peer-reviewed)abstract 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.
12.	Ahuja, Rajeev, et al. (author) High-pressure structural transitions in Cm and Am0.5Cm0.5 binary alloy 2006 In: High Pressure Research. - : Informa UK Limited. - 0895-7959 .- 1477-2299. ; 26:4, s. 377-381 Journal article (peer-reviewed)abstract 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, I 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.
13.	Ahuja, Rajeev, et al. (author) High pressure structural transitions in Cm metal 2006 In: Mater Res Soc Symp Proc. - 1558998470 - 9781558998476 ; , s. 247-254 Conference paper (peer-reviewed)abstract The high pressure behaviour of Cm metal is investigated theoretically using ab initio electronic structure methods. Our calculations reproduce the structural phase transitions which are obsereved in recent experiment performed by Heatman et al. [Science 309, 110 (2005)]. Calculated transition pressures are in reasonable agreement with the experimental values. Calculations performed for an antiferromagnetic state is essential to reproduce the stability of Cm-III phase. Thus, the stability of the Cm-III phase is related to the spin polarization of its 5f electrons.
14.	Ahuja, Rajeev, et al. (author) Optical properties of 4H-SiC 2002 In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 91:4, s. 2099-2103 Journal article (peer-reviewed)abstract The optical band gap energy and the dielectric functions of n-type 4H-SiC have been investigated experimentally by transmission spectroscopy and spectroscopic ellipsometry and theoretically by an ab initio full-potential linear muffin-tin-orbital method. We present the real and imaginary parts of the dielectric functions, resolved into the transverse and longitudinal photon moment a, and we show that the anisotropy is small in 4H-SiC. The measurements and the calculations fall closely together in a wide range of energies.
15.	Ahuja, Rajeev, et al. (author) Optical properties of SiGe alloys 2003 In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 93:7, s. 3832-3836 Journal article (peer-reviewed)abstract The optical properties of Si1-xGex have been investigated theoretically using a full-potential linear muffin-tin-orbital method. We present the density-of-states as well as the real and imaginary parts of the dielectric function. The calculated dielectric function was found to be in good agreement with the spectroscopic ellipsometry measurements by J. Bahng , J. Phys.: Condens. Matter 13, 777 (2001), and we obtained a static dielectric constant of epsilon(0)=12.19+2.45x in the Si rich regime (xless than or equal to0.5).
16.	Ahuja, Rajeev, et al. (author) Relativity and the lead–acid battery 2011 In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 106:1, s. 018301- Journal article (peer-reviewed)abstract 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.
17.	Ahuja, Rajeev, et al. (author) Titanium metal at high pressure : Synchrotron experiments and ab initio calculations 2004 In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 69, s. 184102- Journal article (peer-reviewed)
18.	Allal, Adel, et al. (author) A comparative theoretical investigation of optoelectronic and mechanical properties of KYS2 and KLaS2 2020 In: Materials Science in Semiconductor Processing. - : Elsevier BV. - 1369-8001 .- 1873-4081. ; 113 Journal article (peer-reviewed)abstract 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.
19.	Allal, Adel, et al. (author) 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 calculations 2022 In: Materials Science in Semiconductor Processing. - : Elsevier. - 1369-8001 .- 1873-4081. ; 150 Journal article (peer-reviewed)abstract 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.
20.	Allal, Adel, et al. (author) Structural stability, mechanical, electronic and optical behaviour of RbXS2 (X = Y and La) under high pressure : A first-principle study 2020 In: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 848 Journal article (peer-reviewed)abstract 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.
21.	Alluri, Nagamalleswara Rao, et al. (author) Crystallinity modulation originates ferroelectricity like nature in piezoelectric selenium 2022 In: Nano Energy. - : Elsevier. - 2211-2855 .- 2211-3282. ; 95 Journal article (peer-reviewed)abstract 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.
22.	Almeida, J, et al. (author) Tuning structural, electronic and optical properties of BexZn1-xTe 2006 In: Applied Physics Letters. ; 89, s. 061913- Journal article (peer-reviewed)
23.	Almeida, Roseley, et al. (author) Theoretical Evidence behind Bifunctional Catalytic Activity in Pristine and Functionalized Al2C Monolayers 2018 In: ChemPhysChem. - : Wiley-VCH Verlagsgesellschaft. - 1439-4235 .- 1439-7641. ; 19:1, s. 148-152 Journal article (peer-reviewed)abstract 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.
24.	Alniss, Hasan Y., et al. (author) Investigation of the Factors That Dictate the Preferred Orientation of Lexitropsins in the Minor Groove of DNA 2019 In: Journal of Medicinal Chemistry. - : AMER CHEMICAL SOC. - 0022-2623 .- 1520-4804. ; 62:22, s. 10423-10440 Journal article (peer-reviewed)abstract 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.
25.	Anikina, Ekaterina, et al. (author) Elucidating hydrogen storage properties of two-dimensional siligraphene (SiC8) monolayers upon selected metal decoration 2020 In: Sustainable Energy & Fuels. - : Royal Society of Chemistry (RSC). - 2398-4902. ; 4:11, s. 5578-5587 Journal article (peer-reviewed)abstract 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.
26.	Anikina, Ekaterina, et al. (author) High-capacity reversible hydrogen storage properties of metal-decorated nitrogenated holey graphenes 2022 In: International journal of hydrogen energy. - : Elsevier. - 0360-3199 .- 1879-3487. ; 47:19, s. 10654-10664 Journal article (peer-reviewed)abstract 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.
27.	Anikina, Ekaterina, et al. (author) Li-decorated carbyne for hydrogen storage : charge induced polarization and van't Hoff hydrogen desorption temperature 2020 In: Sustainable Energy & Fuels. - : ROYAL SOC CHEMISTRY. - 2398-4902. ; 4:2, s. 691-699 Journal article (peer-reviewed)abstract 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.
28.	Anikina, Ekaterina, et al. (author) Li-Functionalized Carbon Nanotubes for Hydrogen Storage : Importance of Size Effects 2019 In: ACS APPLIED NANO MATERIALS. - : AMER CHEMICAL SOC. - 2574-0970. ; 2:5, s. 3021-3030 Journal article (peer-reviewed)abstract 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.
29.	Anikina, Ekaterina, et al. (author) Tunning Hydrogen Storage Properties of Carbon Ene-Yne Nanosheets through Selected Foreign Metal Functionalization 2020 In: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 124:31, s. 16827-16837 Journal article (peer-reviewed)abstract 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.
30.	Anikina, E. V., et al. (author) Influence of Kubas-type interaction of B–Ni codoped graphdiyne with hydrogen molecules on desorption temperature and storage efficiency 2020 In: Materials Today Energy. - : Elsevier. - 2468-6069. ; 16 Journal article (peer-reviewed)abstract 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 ~70 meV per H2 molecule on pristine GDY to a maximum of 1.29 eV per H2 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 ~300–500 K. Overall, each Ni adatom on B-doped GDY can bind only one H2 molecule within the needed energy range, which gives low hydrogen uptake (~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.
31.	Anversa, Jonas, et al. (author) High pressure driven superconducting critical temperature tuning in Sb2Se3 topological insulator 2016 In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 108:21 Journal article (peer-reviewed)abstract 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.
32.	Arapan, Sergiu, et al. (author) Determination of the Structural Parameters of an Incommensurate Phase from First Principles : The Case of Sc-II 2009 In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 102:8, s. 085701- Journal article (peer-reviewed)abstract 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.
33.	Arapan, S., et al. (author) Formation of sp(3) hybridized bonds and stability of CaCO3 at very high pressure 2007 In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 98:26 Journal article (peer-reviewed)abstract 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.
34.	Arapan, Sergiu, et al. (author) High-pressure phase transformations in carbonates 2010 In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 82:18, s. 184115- Journal article (peer-reviewed)abstract 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.
35.	Arapan, S., et al. (author) Prediction of incommensurate crystal structure in Ca at high pressure 2008 In: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 105:52, s. 20627-20630 Journal article (peer-reviewed)abstract 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.
36.	Arapan, Sergiu, 1973- (author) Understanding Physical Reality via Virtual Experiments 2008 Doctoral thesis (other academic/artistic)abstract In this thesis I have studied some problems of condensed matter at high pressures and temperatures by means of numerical simulations based on Density Functional Theory (DFT).The stability of MgCO3 and CaCO3 carbonates at the Earth's mantle conditions may play an important role in the global carbon cycle through the subduction of the oceanic crust. By performing ab initio electronic structure calculations, we observed a new high-pressure phase transition within the Pmcn structure of CaCO3. This transformation is characterized by the change of the sp-hybridization state of carbon atom and indicates a change to a new crystal-chemical regime. By performing ab initio Molecular Dynamics simulations we show the new phase to be stable at 250 GPa and 1000K. Thus, the formation of sp3 hybridized bonds in carbonates can explain the stability of MaCO3 and CaCO3 at pressures corresponding to the Earth's lower mantle conditions. We have also calculated phase transition sequence in CaCO3, SrCO3 and BaCO3, and have found that, despite the fact that these carbonates are isostructural and undergo the same type of aragonite to post-aragonite transition, their phase transformation sequences are different at high pressures.The continuous improvement of the high-pressure technique led to the discovery of new composite structures at high pressures and complex phases of many elements in the periodic table have been determined as composite host-guest incommensurate structures. 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 and exploiting the fact that the total energy of the system is a function of structural parameters. By applying this method to the Sc-II phase, we have determined the incommensurate ratio, lattice parameters and Wyckoff positions of Sc-II in excellent agreement with the available experimental data. Moreover, we predict the occurrence of an incommensurate high-pressure phase in Ca from first-principle calculations within this approach.The implementation of DFT in modern electronic structure calculation methods proved to be very successful in predicting the physical properties of a solid at low temperature. One can rigorously describe the thermodynamics of a crystal via the collective excitation of the ionic lattice, and the ab initio calculations give an accurate phonon spectra in the quasi-harmonic approximation. Recently an elegant method to calculate phonon spectra at finite temperature in a self-consistent way by using first principles methods has been developed. Within the framework of self-consistent ab initio lattice dynamics approach (SCAILD) it is possible to reproduce the observed stable phonon spectra of high-temperature bcc phase of Ti, Zr and Hf with a good accuracy. We show that this method gives also a good description of the thermodynamics of hcp and bcc phases of Ti, Zr and Hf at high temperatures, and we provide a procedure for the correct estimation of the hcp to bcc phase transition temperature.
37.	Araujo, Carlos Moyses, et al. (author) Disorder-induced Room Temperature Ferromagnetism in Glassy Chromites 2014 In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 4, s. 4686- Journal article (peer-reviewed)abstract 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.
38.	Araujo, Carlos Moyses, et al. (author) Electronic and optical properties of MgH2: a first-principle GW investigation 2005 In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 98:9, s. 096106- Journal article (peer-reviewed)abstract 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.
39.	Araújo, C. Moysés, et al. (author) Electronic and optical properties of pressure induced phases of MgH2 2005 In: J. Alloys and Compd.. ; 404-406:220 Journal article (peer-reviewed)
40.	Araujo, Carlos Moyses, et al. (author) Electronic and optical properties of pressure induced phases of MgH2 2005 In: Journal of Alloys and Compounds. - 0925-8388. ; 404:16, s. 220- Journal article (peer-reviewed)abstract 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.
41.	Araújo, C. Moysés, et al. (author) Electronic and optical properties of α, γ and β phases of MgH2: a first-principle GW investigation 2005 In: J. Appl. Phys.. ; 98:096106 Journal article (peer-reviewed)
42.	Araújo, C. Moysés, et al. (author) On the structural and energetic properties of the hydrogen absorber Li2Mg(NH)2 2007 In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 91:9, s. 091924- Journal article (peer-reviewed)abstract The authors have performed density functional theory based calculations of several possible conformations for the crystal structure of Li2Mg(NH)2 and they confirm the α phase, resolved from both x-ray and neutron diffraction data, as the ground-state configuration. It is also found that although the N-H bond is stronger in Li2Mg(NH)2 than in Li2NH, hydrogen release from Li2Mg(NH)2/LiH mixture displays more favorable thermodynamics than that from the Li2NH/LiH mixture. The insights gained from this seemingly counterintuitive result should prove helpful in the search for promising hydrogen storage materials.
43.	Araújo, C. Moysés, et al. (author) Pressure-induced phase transition in ErH3 2004 In: Phys. Stat. Sol. (c). ; 241:3219 Journal article (peer-reviewed)
44.	Araujo, Carlos Moyses, et al. (author) Pressure-induced structural phase transition in NaBH4 2005 In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 72:5, s. 054125- Journal article (peer-reviewed)abstract 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 high-pressure phase corresponds to the alpha-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.
45.	Araújo, C. Moysés, et al. (author) Pressure-induced structural phase transition in NaBH4 2005 In: Phys. Rev. B.. ; 72:054125 Journal article (peer-reviewed)
46.	Araujo, Carlos Moyses, et al. (author) Role of titanium in hydrogen desorption in crystalline sodium alanate 2005 In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 86:25 Journal article (peer-reviewed)abstract 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.
47.	Araújo, C. Moysés, et al. (author) Role of titanium in hydrogen desortiption in crystalline sodium Alanate 2005 In: Appl. Phys. Lett.. ; 86:251913, s. 3- Journal article (peer-reviewed)
48.	Araujo, C. Moysés, et al. (author) Room temperature ferromagnetism in pristine MgO thin films 2010 In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 96:23 Journal article (peer-reviewed)abstract 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.
49.	Araújo, C. Moysés, et al. (author) Structural transition in lithium imide triggered by melting of cation sublattice In: Phys. Rev. Lett.. Journal article (peer-reviewed)
50.	Araujo, C. M., et al. (author) Superionicity in the hydrogen storage material Li2NH : Molecular dynamics simulations 2009 In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 79:17 Journal article (peer-reviewed)abstract 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.

Skapa referenser, mejla, bekava och länka

Permalink

Träfflista för sökning "WFRF:(Ahuja Rajeev) "

Refine your search

Year