Browsing by Subject "Lithium compounds"

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    Ab initio study of Ru-terminated and Ru-doped armchair graphene nanoribbons
    (Taylor and Francis, 2012) Sarikavak-Lisesivdin, B.; Lisesivdin, S. B.; Özbay, Ekmel
    We investigate the effects of ruthenium (Ru) termination and Ru doping on the electronic properties of armchair graphene nanoribbons (AGNRs) using first-principles methods. The electronic band structures, geometries, density of states, binding energies, band gap information, and formation energies of related structures are calculated. It is well founded that the electronic properties of the investigated AGNRs are highly influenced by Ru termination and Ru doping. With Ru termination, metallic band structures with quasi-zero-dimensional, one-dimensional and quasi-one-dimensional density of states (DOS) behavior are obtained in addition to dominant one-dimensional behavior. In contrast to Ru termination, Ru doping introduces small but measurable (12.4 to 89.6meV) direct or indirect band gaps. These results may present an additional way to produce tunable band gaps in AGNRs.
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    One-dimensional peptide nanostructure templated growth of iron phosphate nanostructures for lithium-ion battery cathodes
    (American Chemical Society, 2016-06) Susapto, H. H.; Kudu, O. U.; Garifullin, R.; Yllmaz, E.; Güler, Mustafa O.
    Template-directed synthesis of nanomaterials can provide benefits such as small crystalline size, high surface area, large surface-to-volume ratio, and structural stability. These properties are important for shorter distance in ion/electron movement and better electrode surface/electrolyte contact for energy storage applications. Here nanostructured FePO4 cathode materials were synthesized by using peptide nanostructures as a template inspired by biomineralization process. The amorphous, high surface area FePO4 nanostructures were utilized as a cathode for lithium-ion batteries. Discharge capacity of 155 mAh/g was achieved at C/20 current rate. The superior properties of biotemplated and nanostructured amorphous FePO4 are shown compared to template-free crystalline FePO4.
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    Synthesis of mesoporous lithium titanate thin films and monoliths as an anode material for high-rate lithium-ion batteries
    (Wiley-VCH Verlag, 2016) Balcı, F. M.; Kudu, Ö. U.; Yılmaz, E.; Dag, Ö.
    Mesoporous Li4Ti5O12 (LTO) thin film is an important anode material for lithium-ion batteries (LIBs). Mesoporous films could be prepared by self-assembly processes. A molten-salt-assisted self-assembly (MASA) process is used to prepare mesoporous thin films of LTOs. Clear solutions of CTAB, P123, LiNO3, HNO3, and Ti(OC4H9)4 in ethanol form gel-like meso-ordered films upon either spin or spray coating. In the assembly process, the CTAB/P123 molar ratio of 14 is required to accommodate enough salt species in the mesophase, in which the LiI/P123 ratio can be varied between molar ratios of 28 and 72. Calcination of the meso-ordered films produces transparent mesoporous spinel LTO films that are abbreviated as Cxx-yyy-zzz or CAxx-yyy-zzz (C=calcined, CA=calcined–annealed, xx=LiI/P123 molar ratio, and yyy=calcination and zzz=annealing temperatures in Celsius) herein. All samples were characterized by using XRD, TEM, N2-sorption, and Raman techniques and it was found that, at all compositions, the LTO spinel phase formed with or without an anatase phase as an impurity. Electrochemical characterization of the films shows excellent performance at different current rates. The CA40-350-450 sample performs best among all samples tested, yielding an average discharge capacity of (176±1) mA h g−1 at C/2 and (139±4) mA h g−1 at 50 C and keeping 92 % of its initial discharge capacity upon 50 cycles at C/2.
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    Ultraminiature antennas combining subwavelength resonators and a very-high-ε uniform substrate: the case of lithium niobate
    (IEEE, 2020) Serebryannikov, A. E.; Gökkavas, Mutlu; Gündoğdu, Tamara Funda; Volski, V.; Vandenbosch, G. A. E.; Vasylchenko, A.; Özbay, Ekmel
    Combining the effects of subwavelength resonators and very-high-permittivity substrates enables a high extent of miniaturization, even for very simple, split-loop resonators. Here, we demonstrate how requirements to the substrate's permittivity are connected with the desired extent of miniaturization and why materials with a relative permittivity of 30 <; ε <; 100, like lithium niobate, may offer a real possibility to miniaturize. For demonstration purposes, we designed, in line with this approach, an ultraminiature dual-band antenna to operate at 2.8 and 4.2 GHz. The antenna is fabricated using microfabrication techniques and studied experimentally. There is good agreement between the measurement and simulation results. The realized gain is about -5 dB for the first resonance, at which the size of the substrate-resonator block is λ/24. The obtained results demonstrate the potential of the suggested approach, which is expected to be applicable to a very wide class of subwavelength resonators and a wide variety of substrates with high permittivity.