9,137 research outputs found
Low effective mass leading to high thermoelectric performance
High Seebeck coefficient by creating large density-of-states effective mass through either electronic structure modification or manipulating nanostructures is commonly considered as a route to advanced thermoelectrics. However, large density-of-state due to flat bands leads to large transport effective mass, which results in a simultaneous decrease of mobility. In fact, the net effect of such a high effective mass is a lower thermoelectric figure of merit, zT, when the carriers are predominantly scattered by phonons according to the deformation potential theory of Bardeen–Shockley. We demonstrate that the beneficial effect of light effective mass contributes to high zT in n-type thermoelectric PbTe, where doping and temperature can be used to tune the effective mass. This clear demonstration of the deformation potential theory to thermoelectrics shows that the guiding principle for band structure engineering should be low effective mass along the transport direction
Weak electron–phonon coupling contributing to high thermoelectric performance in n-type PbSe
PbSe is a surprisingly good thermoelectric material due, in part, to its low thermal conductivity that had been overestimated in earlier measurements. The thermoelectric figure of merit, zT, can exceed 1 at high temperatures in both p-type and n-type PbSe, similar to that found in PbTe. While the p-type lead chalcogenides (PbSe and PbTe) benefit from the high valley degeneracy (12 or more at high temperature) of the valence band, the n-type versions are limited to a valley degeneracy of 4 in the conduction band. Yet the n-type lead chalcogenides achieve a zT nearly as high as the p-type lead chalcogenides. This effect can be attributed to the weaker electron–phonon coupling (lower deformation potential coefficient) in the conduction band as compared with that in the valence band, which leads to higher mobility of electrons compared to that of holes. This study of PbSe illustrates the importance of the deformation potential coefficient of the charge-carrying band as one of several key parameters to consider for band structure engineering and the search for high performance thermoelectric materials
Reduction of thermal conductivity in PbTe:Tl by alloying with TlSbTe_2
A series of s ingle-phase polycrystalline (TlSbTe_2)_x(Tl_(0.02)Pb_(0.98)Te)_(1-x) (x=0, 0.05, 0.1) compounds were made
to reduce thermal conductivity while maintaining the enhanced Seebeck
coefficients found in PbTe doped with Tl. Transport property
measurements confirmed that high Seebeck coefficients from doping with
Tl are retained by alloying with TlSbTe_2. At the same time, a thermal
conductivity as low as 0.8 W/mK at room temperature, and 0.6 W/mK at
673 K was observed, corresponding to a 30% reduction in lattice
thermal conductivity at 673 K compared with 2% Tl-PbTe. However, the
maximum zT in this system is 0.8 (at 623 K), which is lower than that
of 2% Tl-PbTe prepared in this work (1.2 at 673 K) owing to a decrease
of the charge-carrier mobility when alloying with TlSbTe_2. Possible
influences on the mobility are discussed
First Principles Study of Adsorption of on Al Surface with Hybrid Functionals
Adsorption of molecule on Al surface has been a long standing puzzle
for the first principles calculation. We have studied the adsorption of
molecule on the Al(111) surface using hybrid functionals. In contrast to the
previous LDA/GGA, the present calculations with hybrid functionals successfully
predict that molecule can be absorbed on the Al(111) surface with a
barrier around 0.20.4 eV, which is in good agreement with
experiments. Our calculations predict that the LUMO of molecule is
higher than the Fermi level of the Al(111) surface, which is responsible for
the barrier of the adsorption.Comment: 14 pages, 5 figure
Evolutionary Subnetworks in Complex Systems
Links in a practical network may have different functions, which makes the
original network a combination of some functional subnetworks. Here, by a model
of coupled oscillators, we investigate how such functional subnetworks are
evolved and developed according to the network structure and dynamics. In
particular, we study the case of evolutionary clustered networks in which the
function of each link (either attractive or repulsive coupling) is updated by
the local dynamics. It is found that, during the process of system evolution,
the network is gradually stabilized into a particular form in which the
attractive (repulsive) subnetwork consists only the intralinks (interlinks).
Based on the properties of subnetwork evolution, we also propose a new
algorithm for network partition which is distinguished by the convenient
operation and fast computing speed.Comment: 4 pages, 4 figure
An Evidence Based Time-Frequency Search Method for Gravitational Waves from Pulsar Glitches
We review and expand on a Bayesian model selection technique for the
detection of gravitational waves from neutron star ring-downs associated with
pulsar glitches. The algorithm works with power spectral densities constructed
from overlapping time segments of gravitational wave data. Consequently, the
original approach was at risk of falsely identifying multiple signals where
only one signal was present in the data. We introduce an extension to the
algorithm which uses posterior information on the frequency content of detected
signals to cluster events together. The requirement that we have just one
detection per signal is now met with the additional bonus that the belief in
the presence of a signal is boosted by incorporating information from adjacent
time segments.Comment: 6 pages, 4 figures, submitted to AMALDI 7 proceeding
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