1,743 research outputs found
Understanding the Photocatalytic Activity of La<sub>5</sub>Ti<sub>2</sub>AgS<sub>5</sub>O<sub>7</sub> and La<sub>5</sub>Ti<sub>2</sub>CuS<sub>5</sub>O<sub>7</sub> for Green Hydrogen Production:Computational Insights
[Image: see text] Green production of hydrogen is possible with photocatalytic water splitting, where hydrogen is produced while water is reduced by using energy derived from light. In this study, density functional theory (DFT) is employed to gain insights into the photocatalytic performance of La(5)Ti(2)AgS(5)O(7) and La(5)Ti(2)CuS(5)O(7)—two emerging candidate materials for water splitting. The electronic structure of both bulk materials was calculated by using hybrid DFT, which indicated the band gaps and charge carrier effective masses are suitable for photocatalytic water splitting. Notably, the unique one-dimensional octahedral TiO(x)S(6–x) and tetragonal MS(4) channels formed provide a structural separation for photoexcited charge carriers which should inhibit charge recombination. Band alignments of surfaces that appear on the Wulff constructions of 12 nonpolar symmetric surface slabs were calculated by using hybrid DFT for each of the materials. All surfaces of La(5)Ti(2)AgS(5)O(7) have band edge positions suitable for hydrogen evolution; however, the small overpotentials on the largest facets likely decrease the photocatalytic activity. In La(5)Ti(2)CuS(5)O(7), 72% of the surface area can support oxygen evolution thermodynamically and kinetically. Based on their similar electronic structures, La(5)Ti(2)AgS(5)O(7) and La(5)Ti(2)CuS(5)O(7) could be effectively employed in Z-scheme photocatalytic water splitting
Hidden spontaneous polarisation in the chalcohalide photovoltaic absorber Sn<sub>2</sub>SbS<sub>2</sub>I<sub>3</sub>
Status of the Standard Solar Model Prediction of Solar Neutrino Fluxes
The Standard Solar Model (BP04) predicts a total 8B neutrino flux that is
17.2% larger than measured in the salt phase of the SNO detector (and if it
were significant it will indicate oscillation to sterile neutrinos). Hence it
is important to examine in details uncertainties (and values) of inputs to the
SSM. Currently, the largest fractional uncertainty is due to the new evaluation
of the surface composition of the sun. We examine the nuclear input on the
formation of solar 8B [S17(0)] and demonstrate that it is still quite uncertain
due to ill known slope of the measured astrophysical cross section factor and
thus ill defined extrapolation to zero energy. This yields an additional
reasonably estimated uncertainty due to extrapolation of +0.0 -3.0 eV-b (+0%
-14%). Since a large discrepancy exists among measured as well as among
predicted slopes, the value of S17(0) is dependent on the choice of data and
theory used to extrapolate S17(0). This situation must be alleviated by new
measurement(s). The "world average" is driven by the Seattle result due to the
very small quoted uncertainty, which we however demonstrate it to be an
over-estimated accuracy. We propose more realistic error bars for the Seattle
results based on the published Seattle data.Comment: Fifth International Conferenceon Non-Accelerator New Physics, Dubna,
June 20-25, 2005. Work Supported by USDOE Grant No. DE-FG02-94ER4087
Low-lying continuum structures in B8 and Li8 in a microscopic model
We search for low-lying resonances in the B8 and Li8 nuclei using a
microscopic cluster model and a variational scattering method, which is
analytically continued to complex energies. After fine-tuning the
nucleon-nucleon interaction to get the known 1+ state of B8 at the right
energy, we reproduce the known spectra of the studied nuclei. In addition, our
model predicts a 1+ state at 1.3 MeV in B8, relative to the Be7+p threshold,
whose corresponding pair is situated right at the Li7+n threshold in Li8.
Lacking any experimental evidence for the existence of such states, it is
presently uncertain whether these structures really exist or they are spurious
resonances in our model. We demonstrate that the predicted state in B8, if it
exists, would have important consequences for the understanding of the
astrophysically important Be7(p,gamma)B8 reaction.Comment: 6 pages with 1 figure. The postscript file and more information are
available at http://nova.elte.hu/~csot
Cu<sub>2</sub>SiSe<sub>3</sub> as a promising solar absorber:harnessing cation dissimilarity to avoid killer antisites
Cu₂SiSe₃ as a promising solar absorber: harnessing cation dissimilarity to avoid killer antisites
Copper-chalcogenides are promising candidates for thin film photovoltaics due to their ideal electronic structure and potential for defect tolerance. To this end, we have theoretically investigated the optoelectronic properties of Cu₂SiSe₃, due to its simple ternary composition, and the favourable difference in charge and size between the cation species, limiting antisite defects and cation disorder. We find it to have an ideal, direct bandgap of 1.52 eV and a maximum efficiency of 30% for a 1.5 μm-thick film at the radiative limit. Using hybrid density functional theory, the formation energies of all intrinsic defects are calculated, revealing the p-type copper vacancy as the dominant defect species, which forms a perturbed host state. Overall, defect concentrations are predicted to be low and have limited impact on non-radiative recombination, as a consequence of the p–d coupling and antibonding character at the valence band maxima. Therefore, we propose that Cu₂SiSe₃ should be investigated further as a potential defect-tolerant photovoltaic absorber
A study of nuclei of astrophysical interest in the continuum shell model
We present here the first application of realistic shell model (SM) including
coupling between many-particle (quasi-)bound states and the continuum of
one-particle scattering states to the spectroscopy of 8B and to the calculation
of astrophysical factors in the reaction 7Be(p,gamma)8B.Comment: 9 pages incl. 3 figures, LaTeX with iopart class and epsf. Invited
talk at the Int. Workshop on Physics with Radioactive Nuclear Beams, Jan.
12-17, 1998, Puri, India. Shortened version will be published in proceedings
to apear as a separate J. Phys. G volum
Structure Effects on Coulomb Dissociation of B
Coulomb Dissociation provides an alternative method for determining the
radiative capture cross sections at astrophysically relevant low relative
energies. For the breakup of B on Ni, we calculate the total Coulomb
Dissociation cross section and the angular distribution for E1, E2 and M1. Our
calculations are performed first within the standard first order semiclassical
theory of Coulomb Excitation, including the correct three body kinematics, and
later including the projectile-target nuclear interactions.Comment: 6 pages, proceedings from International Workshop on RNB, Puri, India,
January 1998 - to be published in J. Phys.
Syndromic surveillance to assess the potential public health impact of the Icelandic volcanic ash plume across the United Kingdom, April 2010
The Eyjafjallajökull volcano in Iceland erupted on 14 April 2010 emitting a volcanic ash plume that spread across the United Kingdom and mainland Europe. The Health Protection Agency and Health Protection Scotland used existing syndromic surveillance systems to monitor community health during the incident: there were no particularly unusual increases in any of the monitored conditions. This incident has again demonstrated the use of syndromic surveillance systems for monitoring community health in real time
Frenkel Excitons in Vacancy-Ordered Titanium Halide Perovskites (Cs₂TiX₆)
Low-cost, nontoxic, and earth-abundant photovoltaic materials are long-sought targets in the solar cell research community. Perovskite-inspired materials have emerged as promising candidates for this goal, with researchers employing materials design strategies including structural, dimensional, and compositional transformations to avoid the use of rare and toxic elemental constituents, while attempting to maintain high optoelectronic performance. These strategies have recently been invoked to propose Ti-based vacancy-ordered halide perovskites (A2TiX6; A = CH3NH3, Cs, Rb, or K; X = I, Br, or Cl) for photovoltaic operation, following the initial promise of Cs2SnX6 compounds. Theoretical investigations of these materials, however, consistently overestimate their band gaps, a fundamental property for photovoltaic applications. Here, we reveal strong excitonic effects as the origin of this discrepancy between theory and experiment, a consequence of both low structural dimensionality and band localization. These findings have vital implications for the optoelectronic application of these compounds while also highlighting the importance of frontier-orbital character for chemical substitution in materials design strategies
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