475 research outputs found
First-principles analysis of the interplay between electronic structure and volume change in colquiriite compounds during Li intercalation
A main source of capacity fading in lithium-ion batteries is the degradation
of the active cathode materials caused by the series of volume changes during
charge and discharge cycles. The quaternary colquiriite-type fluorides
LiCaFeF and LiCaCoF were reported to have
negligible volume changes in specific Li concentration ranges, making the
underlying colquiriite structure a promising candidate for so-called
zero-strain behavior. Using first-principles electronic structure calculations
based on density functional theory with a Hubbard- correlation correction on
the transition-metal ions, we systematically investigate the equilibrium
volumes of the colquiriite-type fluorides LiCaMF with M =Ti,
V, Cr, Mn, Fe, Co, and Ni at the Li concentrations =0, 1, and 2. We
elucidate the connection between the total volume of the structures and the
local volumes of fluorine coordinated octahedra around the cations, and we find
trends along the series of the 3d transition-metal elements. In the lithiation
step from =1 to =2 we find volume changes of about 10 %, and we discuss
the discrepancy to the experimentally reported smaller value for
LiCaFeF. From =0 to =1 we describe the compensating
structural mechanisms that lead to an exceptionally small volume change of
LiCaMnF. This compound is therefore a particularly promising
zero-strain cathode material.Comment: 13 pages, 9 Figure
The EVN view of the highly variable TeV active galaxy IC 310
Very-high-energy -ray observations of the active galaxy IC 310 with
the MAGIC telescopes have revealed fast variability with doubling time scales
of less than 4.8min. This implies that the emission region in IC 310 is smaller
than 20% of the gravitational radius of the central supermassive black hole
with a mass of , which poses serious questions on the
emission mechanism and classification of this enigmatic object. We report on
the first quasi-simultaneous multi-frequency VLBI observations of IC 310
conducted with the EVN. We find a blazar-like one-sided core-jet structure on
parsec scales, constraining the inclination angle to be less than but very small angles are excluded to limit the de-projected length
of the large-scale radio jet.Comment: 4 pages, proceedings of the 12th European VLBI Network Symposium and
Users Meeting - EVN 2014, 7-10 October 2014, Cagliari, Italy. Published
online in PoS, ID.10
The prismatic Sigma 3 (10-10) twin bounday in alpha-Al2O3 investigated by density functional theory and transmission electron microscopy
The microscopic structure of a prismatic twin
boundary in \aal2o3 is characterized theoretically by ab-initio
local-density-functional theory, and experimentally by spatial-resolution
electron energy-loss spectroscopy in a scanning transmission electron
microscope (STEM), measuring energy-loss near-edge structures (ELNES) of the
oxygen -ionization edge. Theoretically, two distinct microscopic variants
for this twin interface with low interface energies are derived and analysed.
Experimentally, it is demonstrated that the spatial and energetical resolutions
of present high-performance STEM instruments are insufficient to discriminate
the subtle differences of the two proposed interface variants. It is predicted
that for the currently developed next generation of analytical electron
microscopes the prismatic twin interface will provide a promising benchmark
case to demonstrate the achievement of ELNES with spatial resolution of
individual atom columns
High speed laser tomography system
Article / Letter to editorLeiden Institute of Chemistr
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