Http://prb.aps.org/abstract/PRB/v82/i11/e115314.

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 two-dimensional 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 two-dimensional 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.4–12

Among the various thermoelectric materials, bismuth telluride (Bi2Te3) and its alloys 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 InteractionsDavid 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: