48,121 research outputs found
Predicted Janus monolayer ZrSSe with enhanced n-type thermoelectric properties compared with monolayer
In analogy to transition-metal dichalcogenide (TMD) monolayers, which have
wide applications in photoelectricity, piezoelectricity and thermoelectricity,
Janus MoSSe monolayer has been successfully synthesized by substituting the top
Se atomic layer in by S atoms. In this work, Janus monolayer
ZrSSe is proposed by ab initio calculations. For the electron part, the
generalized gradient approximation (GGA) plus spin-orbit coupling (SOC) is used
as exchange-correlation potential, while GGA for lattice part. Calculated
results show that the ZrSSe monolayer is dynamically and mechanically stable,
which exhibits mechanical flexibility due to small Young's modulus. It is found
that ZrSSe monolayer is an indirect-gap semiconductors with band gap of 0.60
eV. The electronic and phonon transports of ZrSSe monolayer are investigated by
semiclassical Boltzmann transport theory. In n-type doping, the between
ZrSSe and monolayers is almost the same due to similar
outlines of conduction bands. The p-type of ZrSSe monolayer is lower
than that of monolayer, which is due to larger spin-orbit
splitting for ZrSSe than monolayer. The room-temperature sheet
thermal conductance is 33.6 for ZrSSe monolayer, which is
lower than 47.8 of monolayer. Compared to
monolayer, the low sheet thermal conductance of ZrSSe
monolayer is mainly due to small group velocities and short phonon lifetimes of
ZA mode. Considering their and lattice thermal conductivities, the ZrSSe
monolayer may have better n-type thermoelectric performance than
monolayer. These results can stimulate further experimental
works to synthesize ZrSSe monolayer.Comment: 9 pages, 12 figure
Strain effect on power factor in monolayer
Biaxial strain dependence of electronic structures and thermoelectric
properties of monolayer , including compressive and tensile
strain, are investigated by using local-density approximation (LDA) plus
spin-orbit coupling (SOC). Both LDA and LDA+SOC results show that
is a direct gap semiconductor with optimized lattice
constants. It is found that SOC has important effect on power factor, which can
enhance one in n-type doping, but has a obvious detrimental influence for
p-type. Both compressive and tensile strain can induce direct-indirect gap
transition, which produce remarkable influence on power factor. Calculated
results show that strain can induce significantly enhanced power factor in
n-type doping by compressive strain and in p-type doping by tensile strain at
the critical strain of direct-indirect gap transition. These can be explained
by strain-induced accidental degeneracies, which leads to improved Seebeck
coefficient. Calculated results show that n-type doping can provide better
power factor than p-type doping. These results make us believe that
thermoelectric properties of monolayer can be improved in
n-type doping by compressive strain.Comment: 6 pages, 6 figure
Potential thermoelectric material : a first-principles study
The electronic structures and thermoelectric properties of
are investigated by the first-principles
calculations and semiclassical Boltzmann transport theory. Both electron and
phonon transport are considered to attain the figure of merit . A modified
Becke and Johnson (mBJ) exchange potential, including spin-orbit coupling
(SOC), is employed to investigate electronic part of
. It is found that SOC has obvious effect on valence
bands, producing huge spin-orbital splitting, which leads to remarkable
detrimental effect on p-type power factor. However, SOC has a negligible
influence on conduction bands, so the n-type power factor hardly change. The
temperature dependence of lattice thermal conductivity by assuming an inverse
temperature dependence is attained from reported ultralow lattice thermal
conductivity of 0.31 at room temperature.
Calculating scattering time is challenging, but a hypothetical
can be adopted to estimate thermoelectric conversion efficiency. The maximal
figure of merit is up to about 0.70 and 0.60 with scattering time
= s and = s, respectively. These results make
us believe that may be a potential thermoelectric
material.Comment: 5 pages, 6 figures. arXiv admin note: text overlap with
arXiv:1605.0888
Biaxial tensile strain tuned up-and-down behavior on lattice thermal conductivity in -AsP monolayer
Various two-dimensional (2D) materials with graphene-like buckled structure
emerge, and the -phase AsP monolayer has been recently proposed to be
thermodynamically stable from first-principles calculations. The studies of
thermal transport are very useful for these 2D materials-based nano-electronics
devices. Motivated by this, a comparative study of strain-dependent phonon
transport of AsP monolayer is performed by solving the linearized phonon
Boltzmann equation within the single-mode relaxation time approximation (RTA).
It is found that the lattice thermal conductivity () of AsP monolayer
is very close to one of As monolayer with similar buckled structure, which is
due to neutralization between the reduce of phonon lifetimes and group velocity
enhancement from As to AsP monolayer. The corresponding room-temperature sheet
thermal conductance of AsP monolayer is 152.5 . It is noted
that the increasing tensile strain can harden long wavelength out-of-plane (ZA)
acoustic mode, and soften the in-plane longitudinal acoustic (LA) and
transversal acoustic (TA) modes. Calculated results show that of AsP
monolayer presents a nonmonotonic up-and-down behavior with increased strain.
The unusual strain dependence is due to the competition among reduce of phonon
group velocities, improved phonon lifetimes of ZA mode and nonmonotonic
up-and-down phonon lifetimes of TA/LA mode. It is found that acoustic branches
dominate the in considered strain range, and the contribution from
ZA branch increases with increased strain, while it is opposite for TA/LA
branch. By analyzing cumulative with respect to phonon mean free
path (MFP), tensile strain can modulate effectively size effects on
in AsP monolayer.Comment: 8 pages, 13 figure
Thermal Resonance Fusion
We first show a possible mechanism to create a new type of nuclear fusion,
thermal resonance fusion, i.e. low energy nuclear fusion with thermal resonance
of light nuclei or atoms, such as deuterium or tritium. The fusion of two light
nuclei has to overcome the Coulomb barrier between these two nuclei to reach up
to the interacting region of nuclear force. We found nuclear fusion could be
realized with thermal vibrations of crystal lattice atoms coupling with light
atoms at low energy by resonance to overcome this Coulomb barrier. Thermal
resonances combining with tunnel effects can greatly enhance the probability of
the deuterium fusion to the detectable level. Our low energy nuclear fusion
mechanism research - thermal resonance fusion mechanism results demonstrate how
these light nuclei or atoms, such as deuterium, can be fused in the crystal of
metal, such as Ni or alloy, with synthetic thermal vibrations and resonances at
different modes and energies experimentally. The probability of tunnel effect
at different resonance energy given by the WKB method is shown that indicates
the thermal resonance fusion mode, especially combined with the tunnel effect,
is possible and feasible. But the penetrating probability decreases very
sharply when the input resonance energy decreases less than 3 keV, so for
thermal resonance fusion, the key point is to increase the resonance peak or
make the resonance sharp enough to the acceptable energy level by the suitable
compound catalysts, and it is better to reach up more than 3 keV to make the
penetrating probability larger than 10^{-10}.Comment: 4 pages, 3 figure
Isolated highly localized bands in monolayer caused by orbitals
The novel electronic structures can induce unique physical properties in
two-dimensional (2D) materials. In this work, we report isolated highly
localized bands in monolayer by the first-principle
calculations within generalized gradient approximation (GGA) plus spin-orbit
coupling (SOC). It is found that monolayer is an indirect-gap
semiconductor using both GGA and GGA+SOC. The calculations reveal that Yb-
orbitals constitute isolated highly localized bands below the Fermi level at
the absence of SOC, and the bands are split into the and
states with SOC. The isolated highly localized bands can lead to very large
Seebeck coefficient and very low electrical conductivity in p-type doping by
producing very large effective mass of the carrier. It is proved that isolated
highly localized bands have very strong stability again strain, which is very
important for practical application. When the onsite Coulomb interaction is
added to the Yb- orbitals, isolated highly localized bands persist, and
only their relative positions in the gap change. These findings open a new
window to search for novel electronic structures in 2D materials.Comment: 5 pages, 7 figure
Born effective charge removed anomalous temperature dependence of lattice thermal conductivity in monolayer GeC
Due to potential applications in nano- and opto-electronics, two-dimensional
(2D) materials have attracted tremendous interest. Their thermal transport
properties are closely related to the performance of 2D materials-based
devices. Here, the phonon transports of monolayer GeC with a perfect planar
hexagonal honeycomb structure are investigated by solving the linearized phonon
Boltzmann equation within the single-mode relaxation time approximation (RTA).
Without inclusion of Born effective charges () and dielectric constants
(), the lattice thermal conductivity () almost decreases
linearly above 350 K, deviating from the usual law. The
underlying mechanism is because the contribution to from
high-frequency optical phonon modes increases with increasing temperature, and
the contribution exceeds one from acoustic branches at high temperature. These
can be understood by huge phonon band gap caused by large difference in atom
mass between Ge and C atoms, which produces important effects on scattering
process involving high-frequency optical phonon. When considering and
, the phonon group velocities and phonon lifetimes of
high-frequency optical phonon modes are obviously reduced with respect to ones
without and . The reduced group velocities and phonon
lifetimes give rise to small contribution to from high-frequency
optical phonon modes, which produces the the traditional
relation in monolayer GeC. Calculated results show that the isotope scattering
can also reduce anomalous temperature dependence of in monolayer
GeC. Our works highlight the importance of and to
investigate phonon transports of monolayer GeC.Comment: 7 pages, 9 figure
Lower lattice thermal conductivity in SbAs than As or Sb monolayer: a first-principles study
Phonon transports of group-VA elements (As, Sb, Bi) monolayer semiconductors
have been widely investigated in theory, and Sb monolayer (antimonene) of them
has recently been synthesized. In this work, phonon transport of SbAs monolayer
is investigated from a combination of first-principles calculations and the
linearized phonon Boltzmann equation. It is found that the lattice thermal
conductivity of SbAs monolayer is lower than ones of both As and Sb monolayers,
and the corresponding sheet thermal conductance is 28.8 at
room temperature. Calculated results show that group velocities of SbAs
monolayer are between ones of As and Sb onolayers, but phonon lifetimes of SbAs
are smaller than ones of both As and Sb monolayers. Hence, low lattice thermal
conductivity in SbAs monolayer is attributed to very small phonon lifetimes.
Unexpectedly, the ZA branch has very little contribution to the total thermal
conductivity, only 2.4\%, which is obviously different from ones of As and Sb
monolayers with very large contribution. This can be explained by very small
phonon lifetimes for ZA branch of SbAs monolayer. The large charge transfer
from Sb to As atoms leads strongly polarized covalent bond, being different
from As or Sb monolayer. The strongly polarized covalent bond of SbAs monolayer
can induce stronger phonon anharmonicity than As or Sb monolayer, leading to
lower lattice thermal conductivity. It is found that isotope scattering
produces neglectful effect, and the lattice thermal conductivity with the
characteristic length smaller than 30 nm can reach a decrease of about 47\%.
These results may offer perspectives on tuning lattice thermal conductivity by
mixture of multi-elements for applications of thermal management and
thermoelectricity, and motivate further experimental efforts to synthesize
monolayer SbAs.Comment: 7 pages, 8 figure
Phonon transport of three-fold degeneracy topological semimetal MoP
Recently, three-component new fermions in topological semimetal MoP are
experimentally observed, which may have potential applications like topological
qubits, low-power electronics and spintronics. These are closely related to
thermal transport properties of MoP. In this work, the phonon transport of MoP
is investigated by solving the linearized phonon Boltzmann equation within the
single-mode relaxation time approximation (RTA). The calculated
room-temperature lattice thermal conductivity is 18.41 and 34.71 along the in- and cross-plane
directions, exhibiting very strong anisotropy. The isotope and size effects on
the lattice thermal conductivity are also considered. It is found that isotope
scattering produces little effect, and phonon has little contribution to the
lattice thermal conductivity, when phonon mean free path(MFP) is larger than
0.15 at 300 K. It is noted that average room-temperature
lattice thermal conductivity of MoP is lower than that of representative Weyl
semimetal TaAs, which is due to smaller group velocities and larger
Grneisen parameters. Our works provide valuable informations
for the thermal management of MoP-based nano-electronics devices, and motivate
further experimental works to study thermal transport of MoP.Comment: 5 pages, 6 figure
Importance of spin-orbit coupling in power factor calculations for half-Heusler ANiB (A=Ti, Hf, Sc, Y; B=Sn, Sb, Bi)
We investigate the spin-orbit coupling (SOC) effects on the electronic
structures and semi-classic transport coefficients of half-Heusler
(A=Ti, Hf, Sc, Y; B=Sn, Sb, Bi) by using generalized gradient
approximation (GGA). Calculated results show that SOC splits the valence bands
at high symmetry point, and modifies the outline of -centered
valence bands, which has remarkable effects on the electron transport
properties. Thermoelectric properties are performed through solving Boltzmann
transport equations within the constant scattering time approximation. It is
found that the compounds containing Sn atom have larger power factor in p-type
doping than ones in n-type doping, and it is just the opposite for compounds
containing Sb and Bi elements. The SOC has obvious detrimental influence on
power factor in p-type doping, while has a negligible effect in n-type doping.
These can be understood by considering the effects of SOC on the valence bands
and conduction bands. The maximum power factors (MPF) are extracted in n-type
and p-type doping with GGA and GGA+SOC, and the MPF at 300 K with SOC is
predicted to be about 4.25\%44.13\% smaller than that without SOC in the
case of p-type doping for (A=Ti, Hf, Sc, Y; B=Sn, Sb, Bi).
Therefore, it is crucial to consider SOC effects for theoretical analysis in
the case of p-type doping in half-Heusler compounds composed of heavy elements.Comment: 5 pages, 5 figures in Journal of Alloys and Compounds (2016
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