Hiroaki Muta

Thermoelectric properties of rare earth doped SrTiO3

The thermoelectric properties of Sr0.9R0.1TiO3 (R=Y, La, Sm, Gd, Dy) have been measured from room temperature to 1073 K. The electrical conductivities and Seebeck coefficients are independent of the kind of rare earth elements in the temperature range, so the figure of merits are influenced by the difference in the thermal conductivities. The thermal conductivities decrease with doping according to the rare earth atomic mass and ionic radius. Sr0.9Dy0.1TiO3 shows the highest figure of merit of the investigated samples, reaching 3.84×10−4 K−1 at 573 K.

Chalcopyrite CuGaTe2: A High‐Efficiency Bulk Thermoelectric Material

CuGaTe(2) with a chalcopyrite structure demonstrates promising thermoelectric properties. The maximum figure of merit ZT is 1.4 at 950 K. CuGaTe(2) and related chalcopyrites are a new class of high-efficiency bulk thermoelectric material for high-temperature applications.

Ag9TlTe5: A high-performance thermoelectric bulk material with extremely low thermal conductivity

We studied a high-performance thermoelectric material whose chemical formula is Ag9TlTe5. Ag9TlTe5 is simple and easy to prepare. Its highest dimensionless figure of merit (ZT) value is 1.23, obtained at 700K. The values of individual thermoelectric properties at 700K are 2.63×10−4Ωm for electrical resistivity, 319μVK−1 for Seebeck coefficient, and 0.22Wm−1K−1 for thermal conductivity. Ag9TlTe5 is a unique material combining extremely low thermal conductivity and relatively low electrical resistivity.

Thermophysical properties of BaZrO3 and BaCeO3

Abstract Polycrystalline perovskite type oxides, BaZrO 3 and BaCeO 3 , have been prepared by mixing the appropriate amounts of ZrO 2 , CeO 2 , and BaCO 3 followed by reacting at 1273 K and sintering at 1773 K. The thermophysical properties, viz. the thermal expansion coefficient, melting point, elastic moduli, Debye temperature, and Vickers hardness, of BaZrO 3 and BaCeO 3 have been measured. The harmonic and dilatational terms of the heat capacity have been evaluated by using the values of the thermal expansion coefficient, compressibility, and Debye temperature measured in the present study, The relationships between several properties of BaZrO 3 and BaCeO 3 show the typical characteristics of the perovskite type oxides.

Thermoelectric properties of Ag1−xGaTe2 with chalcopyrite structure

In the present study, we investigated the high-temperature thermoelectric (TE) properties of AgGaTe2 with chalcopyrite structure. We tried to enhance the TE properties of AgGaTe2 by reducing the Ag content. The reduction of Ag increased the carrier concentration, leading to enhancement of the dimensionless figure of merit (ZT). The maximum ZT value was 0.77 at 850 K obtained in Ag0.95GaTe2, which was approximately two times higher than that of stoichiometric AgGaTe2.

Thermoelectric properties of NaCo2O4

Abstract The thermoelectric properties such as the thermal conductivity, electrical resistivity and Seebeck coefficient of NaCo 2 O 4 and NaCo 1.9 M 0.1 O 4 (M=Ti, Rh, Pd) were evaluated in the temperature range from room temperature to 723 K. Polycrystalline samples were prepared by sintering in air followed by hot pressing. The thermal conductivity was calculated from the heat capacity, the experimental density, and the thermal diffusivity measured by the laser flash method. The electrical resistivity and Seebeck coefficient were measured simultaneously using ULVAC ZEM-1 in He atmosphere. The dimensionless figure of merit, ZT , of NaCo 1.9 Pd 0.1 O 4 was higher than that of NaCo 2 O 4 over a wide range of temperatures, and reached ZT =0.045 at 723 K.

High-Thermoelectric Figure of Merit Realized in p-Type Half-Heusler Compounds: ZrCoSnxSb1-x

We studied the thermoelectric properties of heavily Sn-doped ZrCoSb half-Heusler compounds, ZrCoSnxSb1-x (x≤0.15), to develop p-type thermoelectric materials. With increasing Sn content x, electrical resistivity decreased and the sign of the thermoelectric power changed from negative to positive. Thermal conductivity was reduced by an alloy scattering effect between Sn and Sb. A high figure of merit (ZT) was obtained: ZT = 0.45 at 958 K in ZrCoSn0.1Sb0.9. This ZT is approximately 2-fold higher than those of the p-type half-Heusler compounds that have been reported to date.

High-temperature thermoelectric properties of thallium-filled skutterudites

The high temperature thermoelectric (TE) properties of polycrystalline Tl-filled skutterudites TlxCo4Sb12 (x=0, 0.05, 0.10, 0.15, 0.20, and 0.25) were examined from room temperature to 750 K. All samples exhibited negative Seebeck coefficients. The electrical resistivity, absolute values of the Seebeck coefficient, and the lattice thermal conductivity were found to decrease with increasing Tl content. Tl0.25Co4Sb12 exhibited the best TE performance; the maximum value for the dimensionless figure of merit ZT was 0.90 at 600 K.

Thermoelectric properties of Tl–X–Te (X=Ge, Sn, and Pb) compounds with low lattice thermal conductivity

We prepared polycrystalline-sintered samples of Tl2GeTe3, Tl4SnTe3, and Tl4PbTe3 and evaluated their thermoelectric properties. Although the electrical properties of these compounds were not optimized, the dimensionless figure of merit ZT was relatively high, i.e., 0.74 at 673K for Tl4SnTe3, 0.71 at 673K for Tl4PbTe3, and 0.29 at 473K for Tl2GeTe3, due to the very low lattice thermal conductivity of the compounds. Low lattice thermal conductivity appears to be closely related to the weak bonding of atoms and complex crystal structures of these compounds.

Thermoelectric properties of Ga-added CoSb3 based skutterudites

Filled skutterudite compounds are known as excellent thermoelectric (TE) materials. It is known that the voids in the structure of the skutterudite compounds, such as CoSb3, can be filled or partially filled with a variety of different atoms, and, thus, obtained filled skutterudite compounds exhibit quite low thermal conductivity (κ). In the present study, we tried to fill Ga into the voids of CoSb3. The polycrystalline samples of GaxCo4Sb12 (x = 0.05, 0.10, 0.15, 0.20, 0.25, and 0.30) were prepared, and the TE properties were examined from room temperature to 750 K. All the samples were composed of two phases: GaxCo4Sb12 (x = ∼0.02) as the matrix phase and Ga metal as the second phase. All the samples exhibited negative values of the Seebeck coefficient (S). The Hall carrier concentration slightly increased with increasing x, while the carrier mobility decreased. Although the maximum Ga filling ratio was really low, the κ was reduced effectively by Ga adding. The maximum value of the dimensionless figure...