Spacer-Inserted Thermoelectric Device and its Reduced $/W in Power Generation

Applied Energy,139, 205(2015)

Right Sizes of Nano- and Microstructures for High-performance and Rigid Bulk  Thermoelectrics

PNAS, 111, 10949 (2014)

Effect of Na Precipitation in NaxPb1-xTe0.85Se0.15 for Thermoelectric Energy Conversion

Journal of Electronic Materials, 43, 353 (2014)

Nanostructured PbTe for Thermoelectric Energy Conversion Device

PbTe based Thermoelectric Nanodot Nanocomposite for Waste Recovery

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  While the thermoelectric generator is clearly advantageous when it generates electricity from the low-quality heat, most of the thermoelectric materials are too expensive to compete against conventional energy conversion devices. To solve these problems, we invented the spacer-inserted thermoelectric device (SITED). This structure is made of thermoelectric material (TEM) and thermally low-conductive dielectric material called a spacer that surrounds the TEM. Instead of the TEM, the spacer can sustain a large temperature difference from a low-quality heat so that the performance in power generation per its material consumption can be innovatively enhanced resulting in low $/W.

  Na is very well known p-type dopant for PbTe system. Because of this, PbTe has a Multi-band structure and high power factor caused by its heavy effective mass. Our research investigated the 3 different route for synthesis and found the size distribution and mean spacing of Na rich precipitations could be different by these 3 method. (1. QH, 2. QAH, 3. AH; each means, Quenching Hot press, Quenching Annealing Hot press, Annealing Hot press). The highest thermoelectric figure of merit, zT, is 2.0 at 773K of QH samples, which is caused by strong phonon scattering by smallest nano-precipitation size(2~6nm).

  Thermoelectric nanocomposite was suggested for increasing thermoelectric conversion efficiency due to the reduction of thermal conductivity. Recent research attempts were made to enhance thermoelectric efficiency by not only reducing thermal conductivity but also increasing power factor. NaxPb1-xTe0.85Se0.15 alloy is representative research that increasing power factor by band engineering. We found that excess Na in PbTeSe system made special microstructures and scattered phonons. In addition, high temperature region over 660K, microstructures start to dissolve and penetrate inside the matrix. Dissolved Na atom supply additional carriers so that electrical conductivity increases after 660K. As a result, thermoelectric figure of merit reach 1.7 at 773K

  Alkali element Na can control the interaction of light- and heavy-hole valence bands. The adjustment of band structure can lead to improvement in electrical properties, especially at higher temperatures. Based on this theory, we have successfully synthesized Na doped PbTe (Na: 2mol%, 2.25mol%) through the melting-quenching method. The pure phase of PbTe which os obtained from XRD data is compared with the microstructure of samples which have abundant nano-scaled precipitates surrounding the main grain. Electrical properties are optimized, and thermal conductivity is reduced. These results contribute to a larger figure of merit zT, 1.29 and 1.41, obtained for 2% and 2.25% respectively.

  Thermoelectric nanocomposite which can lead to thermal conductivity reduction was suggested as a way to increase thermoelectric conversion efficiency. Many studies have reported nanodot nanocomposites which exist as a secondary phase nanodot inside a host crystalline matrix. It is hard to control their intrinsic nanostructure. On the other hand, it is possible to control the nanodot’s size distribution, distance between nanodots, and shape in extrinsic nanodot nanocomposites. Moreover, extrinsic nanodot nanocomposites can be applied to any thermoelectric material. We synthesize the extrinsic nanodot nanocomposite with PbTe fabricated through the ball-mill and hot-press method. By calculating the limit of thermoelectric efficiency of nanostructures, we expect that this can lead to thermoelectric figure of merit (zT) up to ~3.

Journal of Chemistry A, 1, 11269 (2013)