Transcript Current Topics - Electron poor materials

http://prb.aps.org/abstract/PRB/v82/i11/e115314
Conclusion –
None relevant
to us using
bulk
materials.
Phys. Chem. Chem. Phys., 2010, 12, 11900-11904
Self-reorganization of CdTe nanoparticles into twodimensional Bi2Te3/CdTe nanosheets and their
thermoelectrical properties†
Jie Yangab, Yan Gaoa, Jeoung Woo Kimc, Yujian Heb, Rui Song*b, Chi Won Ahn*c and Zhiyong Tang*a
A partial cation exchange reaction between CdTe nanoparticles
and Bi3+ ions gives rise to spontaneous formation of twodimensional Bi2Te3/CdTe nanosheets. The average size and
thickness of the nanosheets are around 200 and 6.9 nm,
respectively. Both CdTe and Bi2Te3, which are there as the form
of nanoparticles with average sizes of 3.4 nm, are found to be
homogenously distributed in the nanosheets. The Bi2Te3/CdTe
nanosheets are further integrated into a pellet by using spark
plasma sintering for optimizing thermoelectric performance.
Compared with the bulk n-type Bi2Te3, the pellets composed of
Bi2Te3/CdTe nanosheets exhibit a considerably low thermal
conductivity, 0.63 W m−1 K−1, and a slightly high
Seebeck coefficient, −182.2 μV K−1, at room
temperature.
Fig. 1 Characterization of Bi2Te3/CdTe nanosheets: (a) XRD pattern, (b) large area SEM
image, (c) low-magnification TEM and a single nanosheet (inset), (d) high-magnification
TEM and a corresponding SAED pattern, (e) and (f) AFM image and a corresponding
cross-section analysis.
Fig. 3 (a) TEM image of the
sintered Bi2Te3/CdTe piece, (b) the
corresponding HRTEM image of
the same sample.
Fig. 4 Temperature
dependence of the electrical
transport properties of the
Bi2Te3/CdTe pellet: (a)
electrical resistivity, (b)
thermal conductivity, (c)
Seebeck coefficient, and (d)
ZT. The inset in (a) is a
photograph of the
Bi2Te3/CdTe platelet sample
used for thermoelectrical
measurement.
Philosophy:
Solid-state cooling and power generation based on thermoelectric effects have
potential applications in energy conservation, e.g. waste-heat recovery,1 as well as
air conditioning2 and refrigeration.3 High-efficiency thermoelectric performance
requires thermoelectric materials with a large thermoeletric figure of merit (ZT), which
is defined as σS2T/κ, where S is the thermopower or Seebeck coefficient, σ is the
electrical conductivity, κ is the thermal conductivity, and T is the absolute
temperature. In order to enhance ZT, a high Seebeck coefficient, an increased
electrical conductivity, and a low thermal conductivity are simultaneously needed.
Currently, there are two general approaches for developing the thermoelectric
materials with high performance: one is to explore new classes of materials with a
high ZT value and the other is to improve the ZT value of the existing materials
through nanotechnology. The introduction of nanostructures into the materials would
induce quantum-confinement effects to enhance the power factor σS2. Furthermore,
the increased internal interfaces formed in nanostructures can scatter phonons more
effectively and thus reduce the thermal conductivity κ of thermoeletric materials.4–
12Among the various thermoelectric materials, bismuth telluride (Bi Te ) and its alloys
2
3
have been a focus of extensive research because of their excellent thermoelectric
performance at near room temperature.13–15 Until now, Bi2Te3-based nanostructures
with various morphologies such as nanoparticles,16–18 nanowires,19,20 nanoplates,21–
24 hollow nanospheres25 and nanotubes26–28 have been prepared by different
methods, e.g., hydro-/solvothermal method,19,29–33 electrodeposition13,34–40 and so on.
Jpn. J. Appl. Phys. 49 (2010) 095205 (7 pagesThermoelectric Effects of Molecular
Quantum Dot Junctions with Strong Electron Phonon
Interactions
David M.-T. Kuo Department of Electrical Engineering and Department of Physics,
National Central University, Chungli 320, Taiwan
We theoretically study the electrical conductance, thermal power,
electron thermal conductance and figure of merit of a single
molecular quantum dot junction using the Anderson model with a
strong coupling of electron–phonon interactions (EPIs). The figure
of merit (ZT) decreases with increasing strength of EPIs. The
suppression of ZT is mainly attributed to a considerable
enhancement of electron thermal conductance. We have
demonstrated that the resolution of thermal power for resolving
multiple phonon-assisted tunneling processes is higher than that
of electrical conductance. Because the Kelvin relation is satisfied,
the Peltier coefficient can also be determined by using measuring
the thermal power.
Philosophy: