2,395 research outputs found
Ferroelectric Materials for Solar Energy Conversion: Photoferroics Revisited
The application of ferroelectric materials (i.e. solids that exhibit
spontaneous electric polarisation) in solar cells has a long and controversial
history. This includes the first observations of the anomalous photovoltaic
effect (APE) and the bulk photovoltaic effect (BPE). The recent successful
application of inorganic and hybrid perovskite structured materials (e.g.
BiFeO3, CsSnI3, CH3NH3PbI3) in solar cells emphasises that polar semiconductors
can be used in conventional photovoltaic architectures. We review developments
in this field, with a particular emphasis on the materials known to display the
APE/BPE (e.g. ZnS, CdTe, SbSI), and the theoretical explanation. Critical
analysis is complemented with first-principles calculation of the underlying
electronic structure. In addition to discussing the implications of a
ferroelectric absorber layer, and the solid state theory of polarisation (Berry
phase analysis), design principles and opportunities for high-efficiency
ferroelectric photovoltaics are presented
Electronic chemical potentials of porous metal-organic frameworks
The binding energy of an electron in a material is a fundamental
characteristic, which determines a wealth of important chemical and physical
properties. For metal-organic frameworks this quantity is hitherto unknown. We
present a general approach for determining the vacuum level of porous
metal-organic frameworks and apply it to obtain the first ionisation energy for
six prototype materials including zeolitic, covalent and ionic frameworks. This
approach for valence band alignment can explain observations relating to the
electrochemical, optical and electrical properties of porous frameworks
Ultra-thin oxide films for band engineering: design principles and numerical experiments
AbstractThe alignment of band energies between conductive oxides and semiconductors is crucial for the further development of oxide contacting layers in electronic devices. The growth of ultra thin films on the surface of an oxide material can be used to introduce a dipole moment at that surface due to charge differences. The dipole, in turn, alters the electrostatic potential — and hence the band energies — in the substrate oxide. We demonstrate the fundamental limits for the application of thin-films in this context, applying analytical and numerical simulations, that bridge continuum and atomistic. The simulations highlight the different parameters that can affect the band energy shifting potential of a given thin-film layer, taking the examples of MgO and SnO2. In particular we assess the effect of formal charge, layer orientation, layer thickness and surface coverage, with respect to their effect on the electrostatic potential. The results establish some design principles, important for further development and application of thin-films for band energy engineering in transparent conductive oxide materials
Quantitative spectroscopy of extreme helium stars - Model atmospheres and a non-LTE abundance analysis of BD+102179?
Extreme helium stars (EHe stars) are hydrogen-deficient supergiants of
spectral type A and B. They are believed to result from mergers in double
degenerate systems. In this paper we present a detailed quantitative non-LTE
spectral analysis for BD+102179, a prototype of this rare class of
stars, using UVES and FEROS spectra covering the range from 3100 to 10
000 {\AA}. Atmosphere model computations were improved in two ways. First,
since the UV metal line blanketing has a strong impact on the
temperature-density stratification, we used the Atlas12 code. Additionally, We
tested Atlas12 against the benchmark code Sterne3, and found only small
differences in the temperature and density stratifications, and good agreement
with the spectral energy distributions. Second, 12 chemical species were
treated in non-LTE. Pronounced non-LTE effects occur in individual spectral
lines but, for the majority, the effects are moderate to small. The
spectroscopic parameters give = 17 300300 K and
= 2.800.10, and an evolutionary mass of 0.550.05 . The star
is thus slightly hotter, more compact and less massive than found in previous
studies. The kinematic properties imply a thick-disk membership, which is
consistent with the metallicity Fe/H and -enhancement.
The refined light-element abundances are consistent with the white dwarf merger
scenario. We further discuss the observed helium spectrum in an appendix,
detecting dipole-allowed transitions from about 150 multiplets plus the most
comprehensive set of known/predicted isolated forbidden components to date.
Moreover, a so far unreported series of pronounced forbidden He I components is
detected in the optical-UV.Comment: Accepted for publication in MNRAS, 26 pages, 19 Figure
Morphological control of band offsets for transparent bipolar heterojunctions:The Bädeker diode
Crystal Structure Generation with Autoregressive Large Language Modeling
The generation of plausible crystal structures is often an important step in
the computational prediction of crystal structures from composition. Here, we
introduce a methodology for crystal structure generation involving
autoregressive large language modeling of the Crystallographic Information File
(CIF) format. Our model, CrystaLLM, is trained on a comprehensive dataset of
millions of CIF files, and is capable of reliably generating correct CIF syntax
and plausible crystal structures for many classes of inorganic compounds.
Moreover, we provide general and open access to the model by deploying it as a
web application, available to anyone over the internet. Our results indicate
that the model promises to be a reliable and efficient tool for both
crystallography and materials informatics
Predicting Thermoelectric Transport Properties from Composition with Attention-based Deep Learning
Thermoelectric materials can be used to construct devices which recycle waste
heat into electricity. However, the best known thermoelectrics are based on
rare, expensive or even toxic elements, which limits their widespread adoption.
To enable deployment on global scales, new classes of effective thermoelectrics
are thus required. models of transport properties can help
in the design of new thermoelectrics, but they are still too computationally
expensive to be solely relied upon for high-throughput screening in the vast
chemical space of all possible candidates. Here, we use models constructed with
modern machine learning techniques to scan very large areas of inorganic
materials space for novel thermoelectrics, using composition as an input. We
employ an attention-based deep learning model, trained on data derived from
calculations, to predict a material's Seebeck coefficient,
electrical conductivity, and power factor over a range of temperatures and
- or -type doping levels, with surprisingly good
performance given the simplicity of the input, and with significantly lower
computational cost. The results of applying the model to a space of known and
hypothetical binary and ternary selenides reveal several materials that may
represent promising thermoelectrics. Our study establishes a protocol for
composition-based prediction of thermoelectric behaviour that can be easily
enhanced as more accurate theoretical or experimental databases become
available
Ultra-thin oxide films for band engineering: design principles and numerical experiments ☆
The alignment of band energies between conductive oxides and semiconductors is crucial for the further development of oxide contacting layers in electronic devices. The growth of ultra thin films on the surface of an oxide material can be used to introduce a dipole moment at that surface due to charge differences. The dipole, in turn, alters the electrostatic potential -and hence the band energies -in the substrate oxide. We demonstrate the fundamental limits for the application of thin-films in this context, applying analytical and numerical simulations, that bridge continuum and atomistic. The simulations highlight the different parameters that can affect the band energy shifting potential of a given thin-film layer, taking the examples of MgO and SnO 2 . In particular we assess the effect of formal charge, layer orientation, layer thickness and surface coverage, with respect to their effect on the electrostatic potential. The results establish some design principles, important for further development and application of thin-films for band energy engineering in transparent conductive oxide materials
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