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Enhanced densification and thermoelectric properties of Ca3Co4O9 ceramics fabricated by solid-state combustion and hot-pressing
(2026-11-15)
Thatawong, Bhoowadol
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Sriondee, Manlika
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Chongsatan, Wistsarut
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Palaporn, Dulyawich
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Pinitsoontorn, Supree
The Ca<inf>3</inf>Co<inf>4</inf>O<inf>9</inf> powders were synthesized by the solid-state combustion method and then calcined at 775-875 °C for 6 h. The combination of combustion-derived fine powders and hot pressing was adopted to improve the densification and thermoelectric (TE) performance of Ca<inf>3</inf>Co<inf>4</inf>O<inf>9</inf> ceramics. Dense Ca<inf>3</inf>Co<inf>4</inf>O<inf>9</inf> ceramics were subsequently fabricated by hot-pressing to investigate the influence of hot-pressing temperature (800-950 °C, 2 h) on phase formation, microstructure, electrical, and TE properties. The Ca<inf>3</inf>Co<inf>4</inf>O<inf>9</inf> powder was obtained after calcination at 800 °C for 6 h and exhibited an average particle size of 0.55 μm. XRD analysis confirmed that Ca<inf>3</inf>Co<inf>4</inf>O<inf>9</inf> was the predominant phase in all hot-pressed samples. XPS analysis further confirmed the presence of oxygen vacancy (V<inf>O</inf>++)-related defects and mixed-valence cobalt species. FESEM observations revealed a dense microstructure composed of plate-like grains with an average grain size ranging from 0.61 to 0.96 μm. The bulk density ranged from 4.31 to 4.46 g/cm3, indicating dense ceramics. The electrical resistivity (ρ) decreased with increasing measured temperature for all samples. Among all samples, the ceramic hot-pressed at 900 °C exhibited the lowest ρ at 600 °C. The Seebeck coefficient (S) significantly increased from 150 μV/K to 223 μV/K, while the thermal conductivity (κ) decreased with increasing temperature. Due to the favorable combination of low ρ and high S, the sample hot-pressed at 900 °C achieved the highest power factor (PF) and a maximum dimensionless figure of merit (ZT) of 0.17 at 600 °C.
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Effect of B doping on electrical and thermal properties of SiC bodies fabricated by spark plasma sintering
(2019-01-01)
Taki, Yukina
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Kitiwan, Mettaya
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Katsui, Hirokazu
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Goto, Takashi
B-doped SiC bodies were fabricated by spark plasma sintering at 2373 K, 50 MPa, 300 s in a vacuum and N<inf>2</inf> atmosphere. The relative density of 1 mol% B doped-SiC body sintered in a vacuum and 5 mol% B doped-SiC body sintered in N<inf>2</inf> atmosphere were 97 and 98%, respectively. The electrical conductivity of B-doped SiC bodies sintered in a vacuum with 0.5 mol% B and that with 1 mol% B sintered in N<inf>2</inf> atmosphere showed semi-insulative conduction in the range of 3-510-3 S m-1 at room temperature. The thermal conductivity of B-doped SiC body at 0.5 at% B sintered in a vacuum were 185 W m-1 K-1 while that at 1 at% B sintered in N<inf>2</inf> atmosphere were 177 W m-1 K-1 at room temperature.
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Influence of Na doping on the thermoelectric properties of CuAlO2 delafossite
(2014-01-01)
Wongcharoen, Ngamnit
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Gaewdang, Thitinai
The polycrystalline Na-doped CuAlO<inf>2</inf> ceramics were obtained by solid state reaction method. The mixture of high purity grade of CuO, Al<inf>2</inf>O<inf>3</inf> and NaNO<inf>3</inf>·6H<inf>2</inf>O powders was ground and then pressed by using uniaxial pressure. The obtained pellet was sintered in air at 1,423 K for 24 h. XRD patterns showed the crystal structure of the as-sintered Cu<inf>1-x</inf>Na<inf>x</inf>AlO<inf>2</inf> (0≤x≤0.05) belonging to rhombohedral, space group R3m along with the CuO and CuAl<inf>2</inf>O<inf>4</inf> phases. The minimum resistivity value around 4.48x102 Ω ·cm and maximum hole concentration around 2.04x1016 cm-3 were observed for x=0.03 at room temperature. The properties of Seebeck coefficient and electrical resistivity were measured in the high temperature ranging 300 to 700 K. The results of electrical resistivity, Seebeck coefficient and power factor values decrease with increasing Na content. The calculated activation energy of conductivity (in the range of 160-250 meV) is larger than that of thermopower (in the range of 26-83 meV) which suggests that the conduction mechanism may be determined as a small polaron hopping type. © (2014) Trans Tech Publications, Switzerland.
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Reinvestigation thermoelectric properties of CuAlO2
(2014-01-01)
Ruttanapun, Chesta
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Kosalwat, Wattana
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Rudradawong, Chalermpol
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Jindajitawat, Phumin
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Buranasiri, Prathan
Bulk CuAlO2 delafossite has been synthesized by solid state reaction to reinvestigate the thermoelectric properties. The electrical conductivity, Seebeck coefficient and thermal conductivity were measured in a high temperature range of 300 to 960 K. The result of positive sign of Seebeck coefficient confirms p-type nature of CuAlO2 compund. The results of bulk sample for Seebeck coefficient, the electrical conductivity and thermal conductivity are range of 900 to 300 μV/K, of 0.01 to 2 S/cm, and of 3.5 W/mK to 1.5 W/mK. The maximum ZT value of bulk sample is 0.017 at a 960 K. These results can be concluded that the bulk CuAlO2 by solid state state displays thermoelelctric material.
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Reinvestigation the thermal and electrical transport properties of Tl7Sb2
(2013-10-29)
Charoenphakdee, Anek
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Harnwunggmoung, Adul
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Seetawan, Tosawat
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Rattanapun, Chesta
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Amornkitbamrung, Vittaya
The authors examined the thermal and electrical transport properties of Tl<inf>7</inf>Sb<inf>2</inf> at temperatures ranging from room temperature to 400 K. The crystal system of Tl<inf>7</inf>Sb<inf>2</inf> is cubic with the lattice parameter a = 1.16053 nm and the space group is Im3m. The polycrystalline samples were prepared by melting stoichiometric amounts of thallium and antimony. Although, usually the thermal conductivity of thallium compounds is very low (<1 Wm-1K-1), that of Tl<inf>7</inf>Sb<inf>2</inf> was relatively high (~13 Wm-1K-1 at room temperature). This is because of the large electronic contribution to the thermal conductivity. © (2013) Trans Tech Publications, Switzerland.
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Designing apparatus for highly precise measurement of electrical conductivity and seebeck coefficient from 85 k to 1200 k
(2013-10-04)
Budngam, Sopon
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Wichainchai, Aree
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Pimmongkol, Saichol
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Tipparach, Udom
We describe the development of apparatus for measuring of electrical conductivity and Seebeck coefficient with high precision from 85 K to 1,200 K. Electrical resistance was measured by means of four-point probe method as a function of temperature. The temperature below 400 K was measured by using type T thermocouple in vacuum system was used and from 400 to 1,200 was measured by using Type S was applied for temperature between 400 and 1200 Kelvin in an inert gas system. With the dimensions of the specimen, the electrical resistivity (ρT) can be obtained in the unit of microohm-centimeter (μΩ - cm) and be written in polynomial, ρ<inf>T</inf> = -0.3191 + 6.8 × 10-3T - 6.0 × 10-7 T2 + 8.0 × 10-10T3. The electrical conductivity can be obtained by taking inversion of the electrical resistivity. Seebeck coefficient (α<inf>T</inf>) can be calculated in microvolt per Kelvin as follows: α<inf>T</inf> = 1.9653 - 1.49 × 10-2T + 9.0 × 10-5T2 - 2.0 × 10-7T3 + 2.0 × 10-10T4 - 1.0 × 10-13T5 + 3.0 × 10-17T6 when T is temperature in K. The Seebeck coefficient data was compared with X-ray diffraction (XRD) and X-ray fluorescence (XRF) of the specimen. The result showed that our developrd apparatus yields the same as standard method when copper with purity greater than 99 percent was employed. © (2013) Trans Tech Publications, Switzerland.
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Structural and thermoelectric properties of zn-doped cuprous aluminate delafossite
(2013-10-04)
Wongcharoen, Ngamnit
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Gaewdang, Thitinai
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Wongcharoen, Tiparatana
The polycrystalline Zn-doped CuAlO<inf>2</inf> ceramics were obtained by solid state reaction method. The mixture of high purity grade of CuO, Al<inf>2</inf>O<inf>3</inf> and Zn(CH<inf>3</inf>COO) <inf>2</inf>{dot operator}2H<inf>2</inf>O powders was ground and then pressed by using uniaxial pressure. The obtained pellet was sintered in air at 1,150 °C for 24 h. XRD patterns showed the crystal structure of the as-sintered CuAl<inf>1-x</inf>Zn<inf>x</inf>O<inf>2</inf> (0≤x≤0.05) belonging to rhombohedral, space group R3m along with the CuO and CuAl2O4 phases. From SEM micrographs, the grain size slightly decreases when the amount of Zn in CuAl<inf>1-x</inf>Zn<inf>x</inf>O<inf>2</inf> samples increases. Hall mobility and hole concentration of the as-sintered samples were obtained from Hall effect measurements in van der Pauw configuration at room temperature. The electrical resistivity measurements as a function of temperature were performed. The variation of Seebeck coefficient and power factor as a function of temperature was also investigated. In the present study, the Zndoped CuAlO<inf>2</inf> ceramics probably have advantages for use in high temperature thermoelectric devices. © (2013)Trans Tech Publications,Switzerland.
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Thermoelectric properties of Ni-doped CuAlO2
(2009-01-01)
Wongcharoen, Ngamnit
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Gaewdang, Thitinai
The polycrystalline Ni-doped CuAlO<inf>2</inf> were obtained by solid state reaction method. The mixture of high purity grade of CuO, Al<inf>2</inf>O <inf>3</inf> and Ni(NO<inf>3</inf>)<inf>2</inf>.6H<inf>2</inf>O powders was ground and then pressed by using uniaxial pressure. The obtained pellet was sintered in air at 1423 K for 24 h. XRD patterns showed the crystal structure of the as-sintered CuAl<inf>1-x</inf>Ni<inf>x</inf>O<inf>2</inf> (0≤ x ≤0.10) belonging to rhombohedral, space group. No evidence of second phase was observed when Ni doping up to x = 0.01. At Ni content x ≥ 0.01 CuAl <inf>1-x</inf>Ni<inf>x</inf>O<inf>2</inf> solid solution phase along with the CuO and CuAl<inf>2</inf>O<inf>4</inf> phases were observed. From SEM micrographs, the grain size decreased from 6 to 2 μm when the amount of Ni in CuAl<inf>1-x</inf>Ni<inf>x</inf>O<inf>2</inf> samples increased. Hall mobility and hole concentration of the as-sintered samples were obtained from Hall effect measurements at room temperature. The activation energy values deduced from the electrical resistivity measurements as a function of temperature were reported. The variation of Seebeck coefficient and power factor as a function of temperature was also investigated. From the experimental results, the substitution of Ni2+ ion in Cu+ site of CuAl <inf>1-x</inf>Ni<inf>x</inf>O<inf>2</inf> material may be drawn. © 2009 Elsevier B.V. All rights reserved.

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