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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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Thickness Dependence of Thermoelectric Properties and Maximum Output Power of Single Planar Sb2Te3 Films
(2022-12-01)
Junlabhut, Prasopporn
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Nuthongkum, Pilaipon
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Harnwunggmoung, Adul
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Limsuwan, Pichet
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Hatayothai, Chanon
P-type Sb<inf>2</inf>Te<inf>3</inf> films with different thicknesses were deposited on polyimide substrates via heat treatment-assisted DC magnetron sputtering. The correlations between the thickness variance and the structure, dislocation density, surface morphology, thermoelectric properties and output power are investigated. As a result, it is clear that the film thickness and the heat treatment process during growth are related to the diffusion of deposited atoms on the substrate surface, leading to imperfection defects inside the films. The imperfections inside the films are affected by their properties. This work also presents the thermoelectric efficiency of a planar single leg of the deposited films with various thicknesses. The maximum power factor is 2.73 mW/mK2 obtained with a film thickness of 9.0 µm and an applied temperature of 100 °C. Planar Sb<inf>2</inf>Te<inf>3</inf> produced a maximum output power of 0.032 µW for a temperature difference of 58 K.
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Simultaneous Seebeck coefficient and electrical conductivity enhancement of GeSbTe films via Sn addition
(2022-06-15)
Khwansungnoen, Phalakorn
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Daichakomphu, Noppanut
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Sukwisute, Pisan
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Limsuwan, Pichet
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Somdock, Nuttakrit
Sn-added GeSbTe (GST) thin films were deposited using a co-magnetron sputtering technique. The effects of varying the Sn content through a variable Sn target sputtering power and post annealing at 673 K were investigated. The DC power density applied to the GST target was controlled at 50 W, while the power density of the Sn target was increased from 0 W to 40 W. The results demonstrate the coexistence of the fcc-GST, hcp-GST and SnTe phases in the Sn-added GST thin films. The substitution of Sn at the Ge-site increases the crystallization speed and leads to defects and lattice disordered local arrangement in the GST films, causing the Seebeck coefficient to increase. The SnTe phase was created as a result of the high Sn content in the sample due to the over-doping limit of Sn into the GST structure. The presence of SnTe in Sn-doped GST films increased the electrical conductivity. The maximum power factor of 17.0 μW/cmK2 at 450 K was obtained at an Sn content of 14.7 at%. These results indicated that the thermoelectric properties of Sn-doped GST films were improved via the formation of an appropriate amount of SnTe composite.
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Improving the photo-thermoelectric performance of CuAlO2 via doping with Bi
(2021-12-01)
Daichakomphu, Noppanut
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Klongratog, Bhanupol
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Rodpun, Phumin
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Pluengphon, Prayoonsak
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Harnwunggmoung, Adul
The photothermoelectric (PTE) effect enables the conversion of temperature differences induced by absorbed light to electrical voltages. For the first time, we investigated the effect of Bi doping on the photothermoelectric properties of CuAlO<inf>2</inf>. In this study, delafossite CuAl<inf>1-x</inf>Bi<inf>x</inf>O<inf>2</inf> (x = 0.01, 0.02, 0.03, 0.04, and 0.06) powders were synthesised. X-ray diffraction and X-ray absorption spectroscopy results indicated that the doping limit of Bi content was approximately 2.6–2.7 at% (x = 0.026–0.027). At x = 0.02, we successfully demonstrated the increase of electrical conductivity due to the reduced effective mass and the increased hole concentration, the increase of optical absorption due to the reduced band gaps, and lower thermal conductivity resulting from mass and strain fluctuations. At a Bi content of 2 at%, the photovoltage signals increased compared with the undoped CuAlO<inf>2</inf>. These results indicated that Bi doping could potentially improve the PTE properties of CuAlO<inf>2</inf>.
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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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Preface
(2021-09-20)
Thammavintorn, Preecha
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Limkaisang, Viroj
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Charoenprakdee, Anek
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Seetawan, Tosawat
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Kimura, Kaoru
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Effect of annealing temperature on thermoelectric properties of bismuth telluride thick film deposited by DC magnetron sputtering
(2020-07-15)
Kianwimol, Supasak
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Sakdanuphab, Rachsak
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Chanlek, Narong
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Harnwunggmoung, Adul
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Sakulkalavek, Aparporn
We report the thermoelectric properties of thick bismuth-telluride (Bi<inf>2</inf>Te<inf>3</inf>) films deposited on polyimide substrates by DC magnetron sputtering and annealed at various temperatures (150–350 °C). The influence of annealing temperature on the microstructure and electronic structure of thick Bi<inf>2</inf>Te<inf>3</inf> films is discussed. In this work, the annealed film at 250 °C has the best thermoelectric property due to highest electrical conductivity and Seebeck coefficient. The main effect of annealing temperature was really helpful to improve crystalline structure and enhance carrier mobility, whereas the carrier concentration was reduced due to the volatile of tellurium atom during annealing. Chemical states of bound and unbound atoms (Bi, Bi3+, Te, and Te2‐) on the surface play an important role in electrical properties. The exceed temperature caused the micro-crack formation and affect carrier transport by the scattering. The power factor of Bi<inf>2</inf>Te<inf>3</inf> deposited by DC magnetron sputtering and annealed at 250 °C is comparable to the power factors of thick Bi<inf>2</inf>Te<inf>3</inf> film deposited by various deposition techniques. The output power of single-leg, thick, thermoelectric Bi<inf>2</inf>Te<inf>3</inf> film annealed at 250 °C as a function temperature generated a power of 0.98 μW at a temperature difference of 50 °C.
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Influence of Sputtering Power Density on the Thermoelectric and Mechanical Properties of Flexible Thermoelectric Antimony Telluride Films Deposited by DC Magnetron Sputtering
(2020-05-01)
Junlabhut, Prasopporn
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Nuthongkum, Pilaipon
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Sakdanuphab, Rachsak
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Harnwunggmoung, Adul
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Sakulkalavek, Aparporn
Antimony telluride (Sb<inf>2</inf>Te<inf>3</inf>) films were deposited on flexible polyimide substrates by DC magnetron sputtering technique using a 99.9% alloy Sb<inf>2</inf>Te<inf>3</inf> target. We measured structural, electrical, thermoelectric and mechanical properties with sputtering power density in the range 30–50 W. X-ray diffraction confirmed that all Sb<inf>2</inf>Te<inf>3</inf> films have high crystallinity with a significant preferential growth along the (015) plane. Surface morphologies were verified by scanning electron microscope: deposited film grain size increased with sputtering power density. The elemental composition was determined by energy dispersive x-ray spectroscopy. Electrical transport properties, carrier concentration, was measured by Hall effect measurement at room temperature. Electrical conductivity and Seebeck coefficient were simultaneously measured by a DC four-terminal method (ZEM-3). The power factor was strongly dominated by electrical conductivity, leading to a maximum of 1.95 mW/K2m with sputtering power 45 W at 300°C. The wettability test, based on the contact angle, evaluated surface energy and hydrophilicity. Nanoindentation was measured on a NHT2 CSM Instrument with diamond Berkovich indenter (B-P 31) at room temperature. The hardness and elastic modulus of deposited Sb<inf>2</inf>Te<inf>3</inf> films increased with the power density.
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Enhancing the thermoelectric properties of sputtered Sb2Te3 thick films via post-annealing treatment
(2020-04-15)
Junlabhut, Prasopporn
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Nuthongkum, Pilaipon
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Sakulkalavek, Aparporn
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Harnwunggmoung, Adul
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Limsuwan, Pichet
Sb<inf>2</inf>Te<inf>3</inf> films of more than 10 μm in thickness were deposited on flexible polyimide substrates by heat treatment-assisted DC magnetron sputtering. The post-annealing parameters including the temperature (150–350 °C) and time (15–60 min) were varied to investigate the microstructure, chemical composition, porosity and thermoelectric properties of the thick films. X-ray diffraction showed that both the as-deposited and post-annealed films were polycrystalline with significant preferential growth along the (015) plane. The films showed slightly off-stoichiometric compositions after post-annealing treatment. Increasing the annealing temperature and annealing time led to an increase in crystalline size and a decrease in porosity of the thick films. This was related to grain growth, agglomeration and surface improvement. The electrical transport and thermoelectric properties including carrier concentration, carrier mobility, electrical conductivity and Seebeck coefficient were investigated using Hall effect measurements and a ZEM-3 apparatus. A maximum power factor of 1.7 mW/K2m was obtained following annealing at 350 °C for 30 min.

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