182 research outputs found
Interfacial strain effects on lithium diffusion pathways in the spinel solid electrolyte Li-doped <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>MgAl</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>4</mml:mn></mml:msub></mml:mrow></mml:math>
No full textThe (Li,Al)-codoped magnesium spinel (LixMg1-2xAl2+xO4) is a solid lithium-ion electrolyte with potential use in all-solid-state lithium-ion batteries. The spinel structure means that interfaces with spinel electrodes, such as LiyMn2O4 and Li4+3zTi5O12, may be lattice matched, with potentially low interfacial resistances. Small lattice parameter differences across a lattice-matched interface are unavoidable, causing residual epitaxial strain. This strain potentially modifies lithium diffusion near the electrolyte-electrode interface, contributing to interfacial resistance. Here, we report a density functional theory study of strain effects on lithium diffusion pathways for (Li,Al)-codoped magnesium spinel, for xLi=0.25 and xLi=0.5. We have calculated diffusion profiles for the unstrained materials, and for isotropic and biaxial tensile strains of up to 6%, corresponding to {100} epitaxial interfaces with LiyMn2O4 and Li4+3zTi5O12. We find that isotropic tensile strain reduces lithium diffusion barriers by as much as 0.32eV, with typical barriers reduced by ∼ 0.1eV. This effect is associated with increased volumes of transitional octahedral sites, and broadly follows qualitative changes in local electrostatic potentials. For biaxial (epitaxial) strain, which more closely approximates strain at a lattice-matched electrolyte-electrode interface, changes in octahedral site volumes and in lithium diffusion barriers are much smaller than under isotropic strain. Typical barriers are reduced by only ∼ 0.05eV. Individual effects, however, depend on the pathway considered and the relative strain orientation. These results predict that isotropic strain strongly affects ionic conductivities in (Li,Al)-codoped magnesium spinel electrolytes, and that tensile strain is a potential route to enhanced lithium transport. For a lattice-matched interface with candidate spinel-structured electrodes, however, epitaxial strain has a small, but complex, effect on lithium diffusion barriers
crystal-torture: A crystal tortuosity module
No full text<p>crystal_torture: A crystal structure analysis code, allowing site tortuosity to be calculated.</p>This work was funded by EPSRC Grant No. EP/N004302/1, and was supported with fund-
ing from the Faraday Institution (faraday.ac.uk; EP/S003053/1), grant number FIRG003.
B.J.M. acknowledges support from the Royal Society (UF130329)
Intrinsic Oxygen Vacancy and Extrinsic Aluminum Dopant Interplay: A Route to the Restoration of Defective TiO2
No full textDensity functional theory (DFT) and DFT corrected for on-site Coulomb interactions (DFT+U) calculations are presented on aluminum doping in bulk TiO2 and the anatase (101) surface. Particular attention is paid to the mobility of oxygen vacancies throughout the doped TiO2 lattice, as a means by which charge compensation of trivalent dopants can occur. The effect that Al doping of TiO2 electrodes has in dye-sensitized solar cells is explained as a result of this mobility and charge compensation. Substitutional defects in which one Al3+ replaces one Ti4+ are found to introduce valence band holes, while intrinsic oxygen vacancies are found to introduce states in the band gap. Coupling two of these substitutional defects with an oxygen vacancy results in exothermic defect formation which maintain charge neutrality. Nudged elastic band calculations have been performed to investigate the formation of these clustered defects in the (101) surface by oxygen vacancy diffusion, with the resulting potential energy surface suggesting energetic gains with small diffusion barriers. Efficiency increases observed in dye sensitized solar cells as a result of aluminum doping of TiO2 electrodes are investigated by adsorbing the tetrahydroquinoline C2-1 chromophore on the defective surfaces. Adsorption on the clustered extrinsic Al3+ and intrinsic oxygen vacancy defects are found to behave as if adsorbed on a clean surface, with vacancy states not present, while adsorption on the oxygen vacancy results in a down shift of the dye localized states within the band gap and defect states being present below the conduction band edge. Aluminum doping therefore acts as a benign dopant for “cleaning” TiO2 through oxygen vacancy diffusion
Adsorption of Thiophene-Conjugated Sensitizers on TiO<sub>2</sub> Anatase (101)
No full textDensity functional theory calculations on the adsorption of the donor−π−acceptor, tetrahydroquinoline (C2-1 and C2-2) and carbazole (JK-24 and JK-25), dyes on the anatase (101) titanium dioxide surface are presented. Increased dye surface coverage is shown to have a much more pronounced effect on the electronic structure than extending the thiophene conjugation length, which has been shown to result from dipole−dipole interactions of the chromophores when forming a monolayer. Thiophene linker moieties are shown to be effective for the control of intramolecular charge separation and optical properties. Increased thiophene conjugation is found to positively shift the highest occupied molecular orbital and can introduce extra occupied states into the band gap
Linear scaling density matrix real time TDDFT: Propagator unitarity and matrix truncation
No full textReal time, density matrix based, time dependent density functional theory (TDDFT) proceeds through the propagation of the density matrix, as opposed to the Kohn-Sham orbitals. It is possible to reduce the computational workload by imposing spatial cutoff radii on sparse matrices, and the propagation of the density matrix in this manner provides direct access to the optical response of very large systems, which would be otherwise impractical to obtain using the standard formulations of TDDFT. Following a brief summary of our implementation, along with several benchmark tests illustrating the validity of the method, we present an exploration of the factors affecting the accuracy of the approach. In particular, we investigate the effect of basis set size and matrix truncation, the key approximation used in achieving linear scaling, on the propagator unitarity and optical spectra. Finally, we illustrate that, with an appropriate density matrix truncation range applied, the computational load scales linearly with the system size and discuss the limitations of the approach
Data Analysis for "Interfacial Strain Effects on Lithium Diffusion Pathways in the Spinel Solid Electrolyte Li-Doped MgAl2O4"
No full textThis repository contains data analysis that supports the findings reported in C. O'Rourke and B. J. Morgan, "Interfacial Strain Effects on Lithium Diffusion Pathways in the Spinel Solid Electrolyte Li-Doped MgAl2O4", and code for plotting figures in this paper
After Columbus: Explaining the Global Trade Boom 1500-1800
No full textThis paper documents the size and timing of the world inter-continental trade boom following the great voyages in the 1490s of Columbus, da Gama and their followers. Indeed, a trade boom followed over the subsequent three centuries. But what was its cause? The conventional wisdom in the world history literature offers globalization as the answer: it alleges that declining trade barriers, falling transport costs and overseas 'discovery' explains the boom. In contrast, this paper reports the evidence that confirms unambiguously that there was no commodity price convergence between continents, something that would have emerged had globalization been a force that mattered. Thus, the trade boom must have been caused by some combination of European import demand and foreign export supply from Asia and the Americas. Furthermore, the behavior of the relative price of foreign importables in European cities should tell us which mattered most and when. We offer detailed evidence on the relative prices of such importables in European markets over the five centuries1350-1850. We then offer a model which is used to decompose the sources of the trade boom 1500-1800.
HyperGUI: Webapp for Hyperspectral Image I/O
No full text<p>Co-Author: Sharon M. O'Rourke <a href="mailto:[email protected]">[email protected]</a></p>
After Columbus: Explaining the Global Trade Boom 1500-1800
No full textThis paper documents the size and timing of the world inter-continental trade boom following the great voyages in the 1490s of Columbus, da Gama and their followers. Indeed, a trade boom followed over the subsequent three centuries. But what was its cause? The conventional wisdom in the world history literature offers globalization as the answer: it alleges that declining trade barriers, falling transport costs and overseas "discovery" explains the boom. In contrast, this paper reports the evidence that confirms unambiguously that there was no commodity price convergence between continents, something that would have emerged had globalization been a force that mattered. Thus, the trade boom must have been caused by some combination of European import demand and foreign export supply from Asia and the Americas. Furthermore, the behavior of the relative price of foreign importables in European cities should tell us which mattered most and when. We offer detailed evidence on the relative prices of such importables in European markets over the five centuries 1350-1850. We then offer a model which is used to decompose the sources of the trade boom 1500-1800.
After Columbus: Explaining the Global Trade Boom 1500-1800
No full textThis paper documents the size and timing of the world inter-continental trade boom following the greate voyages in the 1490s of Columbus, da Gama and their followers. Indeed, a trade boom followed over the subsequent three centuries. But what was its cause? The conventionnal wisdom in the world history literature offers globalization as the answer: it alleges that declining trade barriers falling transport costs and overseas "discovery" explains the boom. In contrast, this paper reports the evidence that confirms unambiguously that there was no commodity price convergence between continents, something that would have emerged had globalization been a force that mattered. Thus, the trade boom must have been caused by some combination of European import demand and foreign export supply from Asia and the Americas. Furthermore, the behavior of the relative price of foreign importables in European cities should tell us which mattered most and when. We offer detailed evidence on the relative prices of such importables in European markets over the five centuries 1350-1850. We then offer a model which is used to decompose the sources of the trade boom 1500-1800.
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