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Enhancement of thermoelectric properties in rapidly synthesised β-Cu2Se using optimized Cu content and microwave hybrid heating
(2024-01-15)
Sakulkalavek, Aparporn
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Rudradawong, Chalermpol
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Gobpant, Jakrit
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Harnwunggmoung, Adul
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Limsuwan, Pichet
To our knowledge, this is the first study to successfully synthesise high-temperature-phase copper selenide (β-Cu<inf>2</inf>Se) at room temperature using rapid microwave hybrid heating (MHH). Controlling the starting Cu/Se ratio is the critical parameter for adjusting the content of α- and β-phases in the as-synthesised sample. The relatively low Cu composition causes impurities to form in the Cu<inf>3</inf>Se<inf>2</inf> phase, deteriorating the thermoelectric (TE) properties of the Cu<inf>2</inf>Se material. The β phase formation at room temperature promotes electrical conductivity. The thermal conductivities of the Cu<inf>2.0</inf>Se samples were 0.5–0.8 Wm−1K−1 at 303–673 K. A strong electronic-phonon interaction may potentially couple electronic thermal conductivity (κ<inf>e</inf>) and lattice thermal conductivity (κ<inf>L</inf>), resulting in incomplete separability of κ<inf>L</inf> and κ<inf>e</inf> in the β-Cu<inf>2.0</inf>Se sample. The Cu<inf>2.0</inf>Se exhibited a ZT value of 0.65 at 523 K because of its considerably lowered thermal conductivity.
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Improving the thermoelectric properties of thick Sb2Te3 film via Cu doping and annealing deposited by DC magnetron sputtering using a mosaic target
(2021-11-01)
Theekhasuk, Nattharika
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Sakdanuphab, Rachsak
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Nuthongkum, Pilaipon
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Pluengphon, Prayoonsak
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Harnwunggmoung, Adul
Thick Cu-doped Sb<inf>2</inf>Te<inf>3</inf> films were deposited on flexible substrate by DC magnetron sputtering from a mosaic Cu–Sb<inf>2</inf>Te<inf>3</inf> target. The Cu-doped Sb<inf>2</inf>Te<inf>3</inf> films were vacuum annealed to improve their thermoelectric properties. Density functional theory was used to clarify the internal mechanism of the Cu doped into the Sb<inf>2</inf>Te<inf>3</inf> system. The results showed that Cu substitution on a Sb site induced electronic states or impurity peaks of Sb<inf>2</inf>Te<inf>3</inf> at a valence band maximum. The carrier concentration of the Cu-doped Sb<inf>2</inf>Te<inf>3</inf> films increased as the Cu-doped concentration increased. However, the crystallite size and Seebeck coefficient of the Cu-doped Sb<inf>2</inf>Te<inf>3</inf> films decreased as the Cu-doped concentration increased. Post-annealing treatment improved the microstructure and thermoelectric properties of the Cu-doped Sb<inf>2</inf>Te<inf>3</inf> films. The maximum electrical conductivity and power factor values of 754.20 S/cm at 50 °C and 1.56 10−3 W/mK2 at 100 °C were obtained in the annealed film with a Cu-doped concentration of 3 at%.
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Energy-saving synthesis and β-phase enhancement of Cu2Se thermoelectric materials via the microwave hybrid heating technique
(2021-10-25)
Rudradawong, Chalermpol
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Sukwisute, Pisan
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Limsuwan, Pichet
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Harnwunggmoung, Adul
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Horprathum, Mati
Thermoelectric generators harvest energy from waste heat and convert it to electricity. β-Cu<inf>2</inf>Se is a candidate for them due to its outstanding thermoelectric properties and its environmentally friendly component elements. A microwave hybrid heating (MHH) method was used for the fast synthesis and enhancement of β-Cu<inf>2</inf>Se materials. The effects of the MHH reaction time on the phase microstructure and thermoelectric properties of the Cu<inf>2</inf>Se material were investigated, and the MHH method was compared with the conventional heating method. The X-ray diffraction patterns of samples, synthesized via the MHH method, showed monoclinic- (α) and cubic- (β) Cu<inf>2</inf>Se crystalline structures, whereas a single monoclinic-(α) structure was identified in a sample, synthesized via a conventional heating method. In addition, the β-Cu<inf>2</inf>Se phase was enhanced with increased MHH reaction time. The carrier concentration increased with β-Cu<inf>2</inf>Se content, which increased electrical conductivity and decreased the Seebeck coefficient. The Cu+ ions in the β-Cu<inf>2</inf>Se phase led to the reduced thermal conductivity. A low thermal conductivity of 0.86 W m−1 K−1 and a maximum dimensionless figure of merit of 0.32 at 523 K were realized for 10 min MHH sample. Finally, MHH showed very low energy consumption and saved time, which are essential for industrialization.
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Effect of real working environment/formation of oxide phase on thermoelectric properties of flexible Sb2Te3 films
(2019-09-01)
Somdock, Nuttakrit
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Harnwunggmoung, Adul
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Sakulkalavek, Aparporn
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Sakdanuphab, Rachsak
Flexible Sb<inf>2</inf>Te<inf>3</inf> thin films, for thermoelectric generator applications, were deposited by DC magnetron sputtering. As-deposited films were annealed in air to simulated a realistic operating environment. The oxidation behavior of the films was studied by monitoring their phase change on exposure to air at different temperatures between 50 and 300 °C for annealing times from 1 to 15 h. Oxidation of Sb and Te formed Sb<inf>2</inf>Te<inf>4</inf> and TeO<inf>2</inf> phases when annealing above 100 °C and Sb<inf>2</inf>Te<inf>3</inf> decomposed into oxide phases at an annealing temperature of 250 °C for 15 h. The thermoelectric performance decreased as the content of Sb<inf>2</inf>O<inf>4</inf> and TeO<inf>2</inf> phases increased. These findings show the limitations of Sb<inf>2</inf>Te<inf>3</inf> films operating in air without vacuum or a protective environment. We propose that the kinetic growth of oxide formation on the Sb<inf>2</inf>Te<inf>3</inf> thin films depend on chemical activation energy and oxygen diffusion through the oxide barrier by the variation of annealing temperature and annealing time, respectively.
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High temperature thermoelectric properties of delafossite CuBO2
(2014-01-01)
Ruttanapun, Chesta
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Jindajitawat, Phumin
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Buranasiri, Prathan
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Thowladda, Warawoot
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Neeyakorn, Worakarn
CuBO<inf>2</inf> is prepared by a solid-state reaction method to investigate thermoelectric properties in high temperature. The XRD result confirms the CuBO<inf>2</inf> compound existing in this method. The Seebeck reveals the compound displays p-type thermoelectric material. The experimental results of electrical resistivity exhibited results of 0.004 S/cm to 0.038 S/cm with the temperature range of 650 to 830 K. The Seebeck value is in the range of 450 μV/K to 950 μV/K, and the thermal conductivity is in the range of 1.4 × 10-5 to 5.3 × 10-5 W/m-K2 with the same temperature. The maximum PF and ZT is 5.3 × 10-5 W/m-K2 and 0.0016, respectively, at 960 K. This work demonstrates that the CuBO<inf>2</inf> delafossite-oxide compound displays the p-type thermoelectric materials. © 2014 IEEE.
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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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