Metal oxides (Ca3Co4O9, CaMnO3, SrTiO3, In2O3), Ti sulfides, and Mn silicides are promising thermoelectric (TE) material candidates for cascade-type modules that are usable in a temperature range of 300–1200 K in air. In this paper, we review previous studies in the field of TE materials development and make recommendations for each material regarding future research. Furthermore, the R&D of TE modules composed of metal oxide materials and the prospect of their commercialization for energy harvesting is demonstrated.

Thermoelectric Ceramics for Energy Harvesting

A significant enhancement of thermoelectric performance in layered oxyselenides BiCuSeO was achieved. The electrical conductivity and Seebeck coefficient of BiCu(1-x)SeO (x = 0-0.1) indicate that the carriers were introduced in the (Cu(2)Se(2))(2-) layer by Cu deficiencies. The maximum of electrical conductivity is 3 × 10(3) S m(-1) for Bicu(0.975)Seo at 650 °C, much larger than 470 S m(-1) for pristine BiCuSeO. Featured with very low thermal conductivity (∼0.5 W m(-1) K(-1)) and a large Seebeck coefficient (+273 μV K(-1)), ZT at 650 °C is significantly increased from 0.50 for pristine BiCuSeO to 0.81 for BiCu(0.975)SeO by introducing Cu deficiencies, which makes it a promising candidate for medium temperature thermoelectric applications.

Remarkable Enhancement in Thermoelectric Performance of BiCuSeO by Cu Deficiencies

We report the dislocation-driven growth of two-dimensional (2D) nanoplates They are another type of dislocation-driven nanostructure and could find application in energy storage, catalysis, and nanoelectronics We first focus on nanoplates of zinc hydroxy sulfate (3Zn(OH)2·ZnSO4·05H2O) synthesized from aqueous solutions Both powder X-ray and electron diffraction confirm the zinc hydroxy sulfate (ZHS) crystal structure as well as their conversion to zinc oxide (ZnO) Scanning electron, atomic force, and transmission electron microscopy reveal the presence of screw dislocations in the ZHS nanoplates We further demonstrate the generality of this mechanism through the growth of 2D nanoplates of α-Co(OH)2, Ni(OH)2, and gold that can also follow the dislocation-driven growth mechanism Finally, we propose a unified scheme general to any crystalline material that explains the growth of nanoplates as well as different dislocation-driven nanomaterial morphologies previously observed through consideration of th

Screw Dislocation-Driven Growth of Two-Dimensional Nanoplates

We report on the structural and electronic transport properties of BiCuSeO based compounds, that have recently been reported as promising thermoelectric materials with figure of merit ZT > 0.8 at 923 K, and share the same crystal structure as the high-Tc iron based 1111 oxypnictides. We show that the substitution of Bi3+ by Sr2+ induces a strong decrease of the electrical resistivity up to the solubility limit reached for x = 0.35, which originates from the strong increase of the carriers concentration. Two anomalies in the resistivity curves have been observed, one for the undoped compound near 260 K and the other for the doped samples at very low temperature. However, structural and magnetic measurements do not provide indications of structural or magnetic phase transition or superconductivity as it had been previously suggested in BiCu1–xOS. We show that the thermoelectric properties of Bi1–xSrxCuSeO materials can be well understood through the analysis of the electronic band structure and the density ...

Structural and Electronic Transport Properties in Sr-Doped BiCuSeO

Comparison of the high temperature thermoelectric properties for Ag-doped and Ag-added Ca3Co4O9

Plate-like particles of Ca3Co4O9 have been prepared in which Bi and Na were partially substituted for Ca to improve the thermoelectric performance. Successfully fabricated dense and highly textured ceramics have been obtained by combining the templated grain growth technique (TGG) with hot-pressing (HP). Ca3Co4O9 single crystals, which have alternating layers of Co–O and Ca–Co–O in the direction of the c-axis, show high electrical conductivity along the layer compared with that across the layer. Hence, a highly oriented TGG + HP specimen showed high electrical conductivity compared with the specimen sintered under uniaxial pressure (UP + PLS). The improved electrical conductivity with high Seebeck coefficient of the highly oriented specimen (TGG + HP) gave a high thermoelectric power factor of 5.9 × 10−4 W m−1 K−2 at 1073 K. The figures-of-merit at 773 K and 1073 K were calculated to be 8.54 × 10−5 K−1
(ZT
= 0.066 at 773 K) and 1.69 × 10−4 K−1
(ZT
= 0.18 at 1073 K), respectively. These values are quite high among Ca–Co–O polycrystalline systems reported so far.

Thermoelectric performance of Bi- and Na-substituted Ca3Co4O9 improved through ceramic texturing

Anisotropic thermoelectric properties of crystal-axis oriented polycrystals of layer-structured oxide in the Ca-Co-O system was discussed. Plate-like particles of (Ca 2.7 Bi 0.3 ) (Co 3.7 Cu 0.3 )O 9+δ were synthesized. To improve the thermoelectric properties, a c-axis oriented polycrystal of (Ca 2.7 Bi 0.3 ) (Co 3.7 Cu 0.3 )O 9+δ was successfully fabricated by uniaxial-pressing and sintering. The electrical conductivity along the ah-plane was about four times larger than that along the c-axis, while the Seebeck coefficients were similar. The thermal conductivity along the ah-plane was more than two times larger than that along the c-axis. The resulting figure-of-merit alone the ab-plane was enhanced due to the enhanced electrical conductivity.

Anisotropic Thermoelectric Properties of Crystal-Axis Oriented Ceramics of Layer-Structured Oxide in the Ca-Co-O System

Background
Among dysmorphic urinary erythrocytes (D cells), G1 cells or doughnut-shaped erythrocytes with one or more blebs are considered to be reliable markers for glomerular diseases. However, although there are many D cells with cytoplasmic color loss and without blebs in the urinary sediment, the significance of these cells is not clear. In this study, we devised a classification system for D cells and examined the relation between these cell types and urinalysis data.

A useful new classification of dysmorphic urinary erythrocytes

We fabricated highly textured Ca/sub 3/Co/sub 4/O/sub 9/-based ceramics by using plate-like particles as a template in order to extract highly anisotropic thermoelectric properties. Plate-like powder and fine powder of (Ca/sub 2.7/Na/sub 0.15/Bi/sub 0.15/)Co/sub 4/O/sub 9/ were synthesized and wet-mixed at the ratio of 1:4. The slurry was tape-cast into a form with the platelets aligned parallel to the tape surface. The tapes were stacked, and sintered or hot-pressed at 1193 K. The resultant ceramics showed highly preferred orientation with the {001} plane parallel to the tape surface. The electrical conductivity in the direction of the ab-plane was improved to 1.8/spl times/10/sup 4/ S/m at 1073 K by the texture given. The maximum power factor reached 5.9/spl times/10/sup -4/ W/mK/sup 2/ at the same temperature.

Daisuke Nagahama

Papers

Thermoelectric performance of Bi- and Na-substituted Ca3Co4O9 improved through ceramic texturing

Anisotropic Thermoelectric Properties of Crystal-Axis Oriented Ceramics of Layer-Structured Oxide in the Ca-Co-O System

A useful new classification of dysmorphic urinary erythrocytes

Thermoelectric properties of Ca/sub 3/Co/sub 4/O/sub 9/-based ceramics textured by templated grain growth method