1,688 research outputs found
A new triclinic modification of the pyrochlore-type KOs2O6 superconductor
A new modification of KOs2O6, the representative of a new structural type
(Pearson symbol aP18, a=5.5668(1)A, b=6.4519(2)A, c=7.2356(2)A, space group
P-1, no.2) was synthesized employing high pressure technique. Its structure was
determined by single-crystal X-ray diffraction. The structure can be described
as two OsO6 octahedral chains relating to each other through inversion and
forming big voids with K atoms inside. Quantum chemical calculations were
performed on the novel compound and structurally related cubic compound.
High-pressure X-ray study showed that cubic KOs2O6 phase was stable up to
32.5(2) GPa at room temperature.Comment: 23 pages, 9 figures,6 tables. Accepted for J. Solid State Che
Oxygen molecule dissociation on carbon nanostructures with different types of nitrogen doping
Energy barrier of oxygen molecule dissociation on carbon nanotube or graphene
with different types of nitrogen doping is investigated using density
functional theory. The results show that the energy barriers can be reduced
efficiently by all types of nitrogen doping in both carbon nanotubes and
graphene. Graphite-like nitrogen and Stone-Wales defect nitrogen decrease the
energy barrier more efficiently than pyridine-like nitrogen, and a dissociation
barrier lower than 0.2 eV can be obtained. Higher nitrogen concentration
reduces the energy barrier much more efficiently for graphite-like nitrogen.
These observations are closely related to partial occupation of {\pi}* orbitals
and change of work functions. Our results thus provide useful insights into the
oxygen reduction reactions.Comment: Accepted by Nanoscal
Achirality in the low temperature structure and lattice modes of tris(acetylacetonate)iron(iii)
Tris(acetylacteonate) iron(III) is a relatively ubiquitous mononuclear inorganic coordination complex. The bidentate nature of the three acetylacteonate ligands coordinating around a single centre inevitably leads to structural isomeric forms, however whether or not this relates to chirality in the solid state has been questioned in the literature. Variable temperature neutron diffraction data down to T = 3 K, highlights the dynamic nature of the ligand environment, including the motions of the hydrogen atoms. The Fourier transform of the molecular dynamics simulation based on the experimentally determined structure was shown to closely reproduce the low temperature vibrational density of states obtained using inelastic neutron scattering
Calculation of solubility in titanium alloys from first-principles
We present an approach to calculate the atomic bulk solubility in binary
alloys based on the statistical-thermodynamic theory of dilute lattice gas. The
model considers all the appropriate ground states of the alloy and results in a
simple Arrhenius-type temperature dependence determined by a {\it
"low-solubility formation enthalpy"}. This quantity, directly obtainable from
first-principle calculations, is defined as the composition derivative of the
compound formation enthalpy with respect to nearby ground states. We apply the
framework and calculate the solubility of the A specie in A-Ti alloys
(A=Ag,Au,Cd,Co,Cr,Ir,W,Zn). In addition to determining unknown low-temperature
ground states for the eight alloys, we find qualitative agreements with
solubility experimental results. The presented formalism, correct in the
low-solubility limit, should be considered as an appropriate starting point for
determining if more computationally expensive formalisms are otherwise needed.Comment: 10 pages, 12 figure
Electronic structure and magnetic properties of the graphene/Fe/Ni(111) intercalation-like system
The electronic structure and magnetic properties of the graphene/Fe/Ni(111)
system were investigated via combination of the density functional theory
calculations and electron-spectroscopy methods. This system was prepared via
intercalation of thin Fe layer (1 ML) underneath graphene on Ni(111) and its
inert properties were verified by means of photoelectron spectroscopy.
Intercalation of iron in the space between graphene and Ni(111) changes
drastically the magnetic response from the graphene layer that is explained by
the formation of the highly spin-polarized quantum-well state in the
thin iron layer.Comment: Manuscript and supplementary material
The melting curve of iron at extreme pressures: implications for planetary cores
Exoplanets with masses similar to that of Earth have recently been discovered
in extrasolar systems. A first order question for understanding their dynamics
is to know whether they possess Earth like liquid metallic cores. However, the
iron melting curve is unknown at conditions corresponding to planets of several
times the Earth's mass (over 1500 GPa for planets with 10 times the Earth's
mass (ME)). In the density-temperature region of the cores of those
super-Earths, we calculate the iron melting curve using first principle
molecular dynamics simulations based on density functional theory. By comparing
this melting curve with the calculated thermal structure of Super Earths, we
show that planets heavier than 2ME, have solid cores, thus precluding the
existence of an internal metallic-core driven magnetic field. The iron melting
curve obtained in this study exhibits a steeper slope than any calculated
planetary adiabatic temperature profile rendering the presence of molten
metallic cores less likely as sizes of terrestrial planets increase
The electronic structure and band gap of LiFePO4 and LiMnPO4
Materials with the olivine LixMPO4 structure form an important new class of
materials for rechargeable Li batteries. There is significant interest in their
electronic properties because of the importance of electronic conductivity in
batteries for high rate applications. The density of states of LixMPO4 (x = 0,
1 and M = Fe, Mn) has been determined with the ab initio GGA+U method,
appropriate for these correlated electron systems. Computed results are
compared with the optical gap of LiFePO4, as measured using UV-Vis-NIR diffuse
reflectance spectroscopy. The results obtained from experiment (3.8-4.0 eV) and
GGA+U computations (3.7 eV) are in very good agreement. However, standard GGA,
without the same level of treatment of electron correlation, is shown to make
large errors in predicting the electronic structure. It is argued that olivines
are likely to be polaronic conductors with extrinsically determined carrier
levels and that their electronic conductivity is therefore not simply related
to the band gap.Comment: 17 pages, 2 figure
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