19 research outputs found
Two-dimensional hybrid composites of SnS2 with graphene and graphene oxide for improving sodium storage: A first-principles study
Among the recent achievements of sodium-ion battery (SIB) electrode
materials, hybridization of two-dimentional (2D) materials is one of the most
interesting appointments. In this work, we propose to use the 2D hybrid
composites of SnS2 with graphene or graphene oxide (GO) layers as SIB anode,
based on the first-principles calculations of their atomic structures, sodium
intercalation energetics and electronic properties. The calculations reveal
that graphene or GO film can effectively support not only the stable formation
of hetero-interface with the SnS2 layer but also the easy intercalation of
sodium atom with low migration energy and acceptable low volume change. The
electronic charge density differences and the local density of state indicate
that the electrons are transferred from the graphene or GO layer to the SnS2
layer, facilitating the formation of hetero-interface and improving the
electronic conductance of the semiconducting SnS2 layer. These 2D hybrid
composites of SnS2/G or GO are concluded to be more promising candidates for
SIB anodes compared with the individual monolayers
Phonon Dispersion Relationship and Oxygen Isotope Effect in Superconductor LaFeAsO
In this paper we calculate ab initially the phonon dispersion relationship of
the superconductor LaFeAsO and investigate a main property in the
superconductor, the oxygen isotope effect. Based on this phonon dispersion
relationship, we find the fact that an important reason of the oxygen isotope
effect is connected with the phonon. This result agrees well with the
experimental data where the power index of the oxygen isotope effect in the
superconductor LaFeAsO is small.Comment: 10 pages, 2 figures, accepted to be published in Int. J. Mod. Phys.
Third-order nonlinearity by the inverse Faraday effect in planar magnetoplasmonic structures
We predict a new type of ultrafast third-order nonlinearity of surface
plasmon polaritons (SPP) in planar magneto-plasmonic structures caused by the
inverse Faraday effect (IFE). Planar SPPs with a significant longitudinal
component of the electric field act via the IFE as an effective transverse
magnetic field. Its response to the plasmon propagation leads to strong
ultrafast self-action which manifests itself through a third-order
nonlinearity. We derive a general formula and analytical expressions for the
IFE-related nonlinear susceptibility for two specific planar magneto-plasmonic
structures from the Lorentz reciprocity theorem. Our estimations predict a very
large nonlinear third-order nonlinear susceptibility exceeding those of typical
metals such as gold
Molecular dynamics study of the effect of moisture and porosity on thermal conductivity of tobermorite 14 \AA
The effect of moisture and porosity on thermal conductivity of tobermorite 14
\AA~as the major component of cement paste is studied by using molecular
dynamics simulation with ClayFF potential. The calculated results show that the
thermal conductivity increases monotonically as the moisture content by mass
within the interior pores increases and the slope of the linear fitting
function decreases as the porosity increases. Meanwhile, the normalized thermal
conductivity is found to increase exponentially as increasing the moisture
content by volume. Phonon density of states of porous and moist tobermorite 14
\AA~is used to explain the contribution of individual atoms and molecules to
the thermal properties. The results can be potentially used to design higher
thermal insulating materials with cement and concrete for energy saving
buildings
Formation and characterization of ceramic coating from alumino silicate mineral powders in the matrix of cement composite on the concrete wall
Enhancement of thermal performance of concrete wall is nowadays of great
importance in reducing the operational energy demand of buildings. We developed
a new kind of inorganic coating material based on \ce{SiO2}-\ce{Al2O3}-rich
minerals and Portland cement (PC) powder. The finely pulverized mineral powder
with the particle size distribution (PSD) of 0.4-40 m was mixed with the
vehicle solvent containing some agents, cement powder with PSD of 2-100 m,
and water in the certain weight ratio, producing the colloid solution. After
application within 2 hours to the plaster layer of concrete wall and sufficient
long hardening period of over three months, the coating layer of 0.6-1.0 mm
thickness was observed to become a densified ceramic. Powder X-ray diffraction
(XRD) experiments were performed to identify the crystalline components of
minerals, cement and ceramic coating powders. Three- and two-dimensional
surface morphologies and chemical compositions of coating material were
obtained with the optical interferometer and scanning electron microscope (SEM)
equipped with an energy dispersive X-ray analyzer (EDX). These XRD and SEM/EDX
analyses demonstrated obviously that the coating layer is mainly composed of
the calcium-silicate-hydrate (C-S-H) and the calcium-aluminate-hydrate (C-A-H)
ceramics with the relatively small number of closed pores (10\% porosity)
compared with the cement mortar and concrete layers. Two-step hydrations of
cement and subsequently \ce{SiO2}-\ce{Al2O3} promoted by the alkali product
\ce{Ca(OH)2} were proposed as the main mechanism of ceramic formation
Influence of Ti/V Cation-Exchange in NaTiO on Na-Ion Negative Electrode Performance: an Insight from First-Principles Study
Sodium-titanate \ce{Na2Ti3O7} (NTO) is regarded as a highly promising anode
material with a very low voltage for Na-ion batteries and capacitors, but
suffered from relatively low specific capacity and poor electron conductivity.
Here we report a first-principles study of electrochemical properties of NTO
and its vanadium-modified compounds, \ce{Na2Ti2VO7} and \ce{Na2TiV2O7} (NTVO),
offering an insight into their detailed working mechanism and an evidence of
enhancing anode performance by Ti/V cation exchange. Our calculations reveal
that the specific capacity can increase from 177 mAh g in NTO to over
280 mAh g in NTVO when using \ce{NaTi_{3-}V_{}O7} ( = 1, 2) as
a starting material for Na insertion due to higher oxidation state of
\ce{V^{+5}}, together with lower voltages and small volume expansion rates
below 3\%. With Ti/V exchange, we obtain slightly higher activation energies
for Na ion migrations along the two different pathways, but find an obvious
improvement of electronic transport in NTVO
Ultracompact high-contrast magneto-optical disk resonator side-coupled to a plasmonic waveguide and switchable by an external magnetic field
Here we propose and study a novel type of plasmonic resonators based on a
metal-insulator-metal waveguide and a side-coupled magneto-optical disk
controlled by an external magnetic field. The wavenumber change and the
transmission of surface-plasmon-polaritons (SPPs) can be tuned by altering the
magnetic field and reversible on/off switching of the running SPP modes by a
reversal of the direction of the external magnetic field is demonstrated.
Resonant enhancement of the magneto-plasmonic modulation by more than 200 times
leads to a modulation contrast ratio more than tenfold ratio (90-\%-modulation)
keeping a moderate insertion loss within an optical bandwidth of hundreds of
GHz. Numerical simulations confirm the predictions by the derived analytical
formulas of a high-contrast magneto-plasmonic modulation by the submicron
ultra-small disk resonator
Competing electronic orders on a heavily doped honeycomb lattice with enhanced exchange coupling
Motivated by recent discovery of correlated insulating and superconducting
behavior in twisted bilayer graphene, we revisit graphene's honeycomb lattice
doped close to the van Hove singularity, using the truncated unity functional
renormalization group approach. We consider an extended Hubbard model on the
honeycomb lattice including on-site and nearest-neighbor Coulomb repulsions,
and nearest-neighbor ferromagnetic exchange and pair hopping interactions. By
varying the strength of the nearest-neighbor exchange coupling and Coulomb
repulsion as free parameters, we present rich ground-state phase diagrams which
contain the spin-triplet -wave and spin-singlet chiral -wave
superconducting phases, the commensurate and incommensurate spin- and
charge-density-wave phases, and the ferromagnetic phase. In the absence of the
exchange coupling and for small value of the nearest-neighbor repulsion, the
four-sublattice spin-density-wave phase is generated right around the van Hove
filling, while the chiral -wave superconductivity emerges slightly away from
it. Surprisingly, the chiral -wave superconductivity is strongly suppressed
by weak nearest-neighbor exchange coupling in our calculations. We argue that
this suppression might be one of the reasons why the chiral superconductivity
proposed for doped graphene has not yet been observed experimentally.Comment: 20 pages, 11 figures, 2 table
All-optical magnetization switching by two-frequency pulses using the plasmon-induced inverse Faraday effect in a magneto-plasmonic structure
In this Letter we study the generation of quasi-static magnetic fields by the
plasmon-induced inverse Faraday effect and propose a magneto-optical waveguide
structure for achieving magnetization switching at sub-ps time in a
nano-confined magneto-optical structure. In particular we show that the
direction of the generated quasi-static field in a magneto-optical dielectric
cavity side-coupled to a metal-insulator-metal (MIM) waveguide depends
sensitively on the wavelength of the surface plasmon polaritions (SPP). This
phenomenon could open up a new energy-efficient ultrafast method for
nano-confined all-optical magnetization switching by two-frequency pulses
First-Principles Study on NaxTiO2 with Trigonal Bipyramid Structures: An Insight into Sodium-Ion Battery Anode Application
Developing efficient anode materials with low electrode voltage, high
specific capacity and superior rate capability is urgently required on the road
to commercially viable sodium-ion batteries (SIBs). Aiming at finding a new SIB
anode material, we investigate the electrochemical properties of NaxTiO2
compounds with unprecedented penta-oxygen-coordinated trigonal bipyramid (TB)
structures by using the first-principles calculations. Identifying the four
different TB phases, we perform the optimization of their crystal structures
and calculate their energetics such as sodium binding energy, formation energy,
electrode potential and activation energy for Na ion migration. The
computations reveal that TB-I phase can be the best choice among the four TB
phases for the SIB anode material due to relatively low volume change under 4%
upon Na insertion, low electrode voltage under 1.0 V with a possibility of
realizing the highest specific capacity of ~335 mAh/g from fully sodiation at x
= 1, and reasonably low activation barriers under 0.35 eV at the Na content
from x = 0.125 to x = 0.5. Through the analysis of electronic density of states
and charge density difference upon sodiation, we find that the NaxTiO2
compounds in TB phases change from electron insulating to electron conducting
material due to the electron transfer from Na atom to Ti ion, ordering the Ti
4+/Ti 3+ redox couple for SIB operation