Rudradawong, Chalermpol

Preferred name

Alternative Name

Rudradawong, C.

Main Affiliation

School of Science

chalermpol.ru@kmitl.ac.th

Now showing 1 - 10 of 21

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Tuning the thermoelectric performance of flexible copper selenide thin films through sputtering pressure and hybrid microwave annealing
(2025-10-10)
Khuncharoen, Wasan
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Theekhasuk, Nattharika
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Rudradawong, Chalermpol
;
Voraud, Athorn
;
Sakdanuphab, Rachsak
Flexible copper selenide (Cu₂₋ₓSe) thin films were deposited on polyimide substrates by direct current magnetron sputtering under varying pressures (0.8–4.0 × 10⁻² mbar) and subsequently annealed using hybrid microwave irradiation at 250 °C for 10–30 min. Increasing sputtering pressure raised the copper content (62.2–63.8 at%) and suppressed the formation of Cu₃Se₂ impurities. Hybrid microwave annealing promoted the transformation to stoichiometric β-Cu₂Se, removed oxide phases such as selenium dioxide and copper oxide, and improved crystallinity, as confirmed by x-ray diffraction and x-ray photoelectron spectroscopy. Field-emission scanning electron microscopy revealed microstructural densification at 10–20 min, whereas 30 min induced cracks and porosity that degraded transport properties. The optimized 20-minute annealed film achieved a peak power factor of 81.5 × 10⁻⁵ W/m·K² at 300 °C—over 130 times higher than that of the as-deposited film and comparable to other flexible Cu₂Se systems. Stability tests confirmed excellent retention after three months of ambient storage. These results establish sputtering pressure control and hybrid microwave annealing as scalable strategies for high-performance, stable Cu₂Se thermoelectric films.
3
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High temperature electrical and thermal properties of activated bamboo charcoal/C12A7 mayenite composite prepared by carbon diffusion process
(2019-03-15)
Rudradawong, Chalermpol
;
Ruttanapun, Chesta
Activated carbon from bamboo charcoal (BC) was diffused into the C12A7 mayenite compound via carbon diffusion process for synthesizing BC and C12A7 composite (BC/C12A7 composite). The BC/C12A7 composite was fabricated by carbon diffusion at holding time 5, 10 and 20 h for investigating electrical and thermal properties at high temperature. Result of XRD revealed the C12A7 structure and confirmed by Raman spectrum. Obtained energy gap showed at 4.93, 5.26, 5.19 and 5.09 eV at holding times of 0, 5, 10 and 20 h, respectively. Electrical conductivity significantly increased with increasing temperature and increased as a function of increasing holding time. Carrier concentration showed approximately 1.27 × 10 17 , 1.32 × 10 17 and 2.76 × 10 17 cm −3 of 5, 10 and 20 h, respectively. Temperature dependence of thermal conductivity showed as proportion of T −1 due to phonon-phonon scattering of Umklapp process. The thermal conductivity decreased from pristine C12A7 approximately 0.4 W m −1 K −1 in all BC/C12A7 composite samples.
7
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Dual optimization of ZT and output power in bulk Bi2Te3 through metal-assisted chemical etching
(2026-03-01)
Theekhasuk, Nattharika
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Sakulkalavek, Aparporn
;
Ono, Takahito
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Sakdanuphab, Rachsak
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Nguyen, Duc Nam
Thermoelectric materials offer a promising route for sustainable energy harvesting by directly converting waste heat into electricity, enabling compact, solid-state, and environmentally friendly energy solutions. Among them, bismuth telluride (Bi₂Te₃) stands out as the benchmark material for near-room-temperature applications due to its excellent electronic transport properties and commercial maturity. However, achieving high-performance in bulk or thick-film Bi₂Te₃ remains a formidable challenge. Conventional strategies such as doping, alloying, and nanoinclusion, while successful in thin films, often fail to translate effectively to bulk systems due to issues like pore collapse, poor uniformity, and degraded electrical connectivity. These limitations hinder the formation of efficient phonon-scattering architectures without compromising charge transport, resulting in limited improvement in the thermoelectric figure of merit (ZT). In this study, we present a novel and scalable nanoengineering strategy that applies metal-assisted chemical etching (MACE) to fabricate nanoporous surface layers on bulk Bi₂Te₃ for the first time. Unlike conventional nanostructuring techniques, MACE enables the formation of oriented nanostructures via a simple wet-chemical process, offering high tunability, low cost, and compatibility with large-area substrates. To reduce interfacial resistance, nickel was subsequently electrodeposited onto the nanostructured surface, forming a conformal contact layer that improves charge extraction and output performance. By systematically tuning the MACE duration, the optimized nanostructured Bi₂Te₃ sample exhibited a 2.3-fold improvement compared to the pristine bulk sample. Furthermore, due to the increased surface area from the nanoporous architecture, the internal resistance and output power of the nanostructured Bi₂Te₃ devices demonstrated 25-fold and 5.8-fold improvments, respectively, relative to the untreated sample. These remarkable improvements are attributed to the synergistic effect of enhanced phonon scattering within the nanoporous layer and improved charge transport enabled by the conformal nickel coating. This work not only introduces a powerful nanostructuring route for Bi₂Te₃ but also establishes a practical platform for high-performance, thick-film thermoelectric devices. The findings offer deep insight into the structure, property, and performance relationships governing thermoelectric efficiency and pave the way toward the scalable fabrication of next-generation thermoelectric modules for real-world applications such as industrial waste heat recovery and self-powered electronics.
2
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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
;
Rudradawong, Chalermpol
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Gobpant, Jakrit
;
Harnwunggmoung, Adul
;
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.
3
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Effect of excess oxygen for CuFeO2.06 delafossite on thermoelectric and optical properties
(2017-12-01)
Rudradawong, Chalermpol
;
Ruttanapun, Chesta
This work presents the role of excess oxygen in CuFeO<inf>2.06</inf> compounds on thermoelectric and optical properties. The CuFeO<inf>2.06</inf> specimens were synthesized by solid state reaction method. X-ray diffraction technique has confirmed the CuFeO<inf>2</inf> structure for the specimens. In particularly, CuFeO<inf>2.06</inf> specimen revealed the structural extension of lattice parameter: a and c. Also, the specimen found increasing excess oxygen of approximately 3% as a resulted enhancement of mixed valence state of Cu+ and Cu2+ ions. XPS showed mixed valence state of the Cu+/Cu2+ ions, and Fe3+ and Fe2+ ions was also found in the CuFeO<inf>2.06</inf> specimen. Mixed valence states contributed the co-existence of hole and electron carriers for conduction. Consequently, electrical conductivity of the CuFeO<inf>2.06</inf> specimen increased up to 23 S/cm at 873 K. Also, increasing Seebeck coefficient was shown to be approximately 302 μV/K at 873 K. The CuFeO<inf>2.06</inf> specimen was found power factor to be approximately 2.1 × 10−4 W/m∙K2 at 873 K. The indirect optical gap of CuFeO<inf>2.06</inf> (2.40 eV) was lower than that of the CuFeO<inf>2</inf> (2.60 eV). Thus, thermoelectric and optical properties were governed by an existence of excess oxygen.
1
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Optimizing fabrication processes for scalable production of flexible thermoelectric modules: A case study on self-powered IoT systems
(2025-09-01)
Gobpant, Jakrit
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Klongratog, Bhanupol
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Rudradawong, Chalermpol
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Sakdanuphab, Rachsak
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Limsuwan, Pichet
This study explores the optimization of fabrication processes for flexible thermoelectric generators (FTEGs) to enhance their performance and scalability for industrial applications, with a focus on integrating them into self-powered Internet of Things (IoT) systems. The research investigates the impact of silicone layer thickness and applied fabrication pressures on the mechanical stability, energy harvesting efficiency, and power output of FTEGs. Results demonstrate that reducing the thermal conductivity of the silicone filler and optimizing the fabrication pressure significantly improves the performance of FTE modules. The optimized FTEGs, featuring a series-parallel configuration, achieve a power density of 5.2 mW/cm² under a temperature difference of 50 °C, surpassing prior benchmarks. The developed system efficiently harvests waste heat, charges a battery, and powers an IoT module for real-time monitoring of temperature, humidity, and carbon monoxide levels. These findings highlight the potential of FTEGs as a sustainable solution for energy harvesting and self-powered industrial monitoring applications.
2
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Enhanced thermoelectric properties of Cu2Se via Sb doping: An experimental and computational study
(2023-02-01)
Rudradawong, Chalermpol
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Khammuang, Satchakorn
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Kotmool, Komsilp
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Bovornratanaraks, Thiti
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Limsuwan, Pichet
In this study, Cu<inf>2</inf>Se<inf>1−x</inf>Sb<inf>x</inf> (x = 0.000, 0.005, 0.010, and 0.015) thermoelectric materials were synthesised using a solid-state reaction technique. A first-principles calculation indicated that the formation energy of the substitution of antimony (Sb) on the Se site is negative and more stable than those of copper (Cu) sites. Sb doping enhanced the lamellar orientation, decreased the grain size, and created an acceptor impurity level. The electrical resistivity and Seebeck coefficient decreased with increasing Sb doping. A minimum reduction in the thermal conductivity by approximately three times that of the undoped sample was obtained at x = 0.005 with a value of 0.40 W/m K at 523 K. The maximum figure of merit (ZT) was obtained at x = 0.005 with a value of 0.47 at 523 K. These findings indicate that substituting Sb into Se sites is an efficient approach for improving copper selenide (Cu<inf>2</inf>Se) thermoelectric materials.
2
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Improvement of Thermoelectric Material by Reduction Thermal Conductivity of Sn-doped CuFeO2 Delafossite Compound
(2015-09-02)
Hongaromkij, Y.
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Rudradawong, C.
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Wichainchai, A.
;
Ruttanapun, C.
In this work, the polycrystalline CuFe1-xSnxO2 (x = 0.005, 0.01, 0.03) were synthesized by a solid state reaction method with sintering temperature at 1323K for 40 hours. The XRD pattern and TGA results showed the crystal structure of hexagonal delafossite-type structure for space group (166). Thermal conductivity was decreased because the large atomic mass of the Sn substituted to the Fe sites of CuFeO2. This caused phonon scattering by the point defect of the mass difference between Sn atom and Fe atom. The minimal value of the thermal conductivity was 2.1 W/mK at 573K for Sn = 0.03. © 2015
3
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Combined effects of Mg reducing and Sn doping on the electrical conductivity of polycrystalline Ca12Al14O33 mayenite
(2019-04-01)
Rudradawong, Chalermpol
;
Ruttanapun, Chesta
Polycrystalline Ca<inf>12</inf>Al<inf>14</inf>O<inf>33</inf> was prepared by a solid state reaction method. All samples showed the phase of the Ca<inf>12</inf>Al<inf>14</inf>O<inf>33</inf> by X-ray powder diffraction (XRD). The Mg heat treatment and Sn doping contributions dominated to increase the lattice constant a from 11.909(3) to 12.163(1) Å. Electron excitation energy of all samples were assigned by absorption spectra. The excitation energy between 2.68 and 2.79 eV was found after the Mg heat treatment. Electrical conductivity increased approximately 109 orders of magnitude at room temperature when experiencing Mg heat treatment for 10 h. The highest electrical conductivity obtained from the Ca<inf>12</inf>Al<inf>12.8</inf>Sn<inf>1.2</inf>O<inf>33</inf>/Mg(10) sample was 7.65 S cm− 1 at 573 K. The low activation energy for electrical conductivity was approximately 0.038 eV as a result of the Mg heat treatment. The influence of the Sn doping excellence supported the increase of the electrical conductivity with the Mg heat treatment process.
6
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Flexible thermoelectric generator with radiative cooling for body-heat-driven self-powered Bluetooth low energy sensing system
(2025-10-01)
Gobpant, Jakrit
;
Van Toan, Nguyen
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Ono, Takahito
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Tuoi, Truong Thi Kim
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Tran, Ngoc Dang Khoa
Wearable electronics and wireless IoT sensors are increasingly expected to operate in a self-powered manner. However, their practical deployment remains limited due to the lack of compact, flexible, and sustainable energy sources. Thermoelectric generators (TEGs), which convert body heat into electricity, present a promising solution but are typically hindered by small temperature gradients and the requirement of bulky heat sinks that compromise flexibility. To address these challenges, we developed an ultra-thin flexible thermoelectric generator (FTEG) integrated with a radiative cooling (RC) layer that passively enhances heat dissipation under natural convection. The device, fabricated using high-performance thermoelectric materials on a soft silicone substrate, maintained a total thickness of just 2.26 mm. Finite element modeling and experimental validation confirmed that the RC layer effectively increased the temperature gradient across thermoelectric legs, significantly improving the output power compared to conventional graphite-based or no-cooling designs. The FTEG achieved a maximum normalized power density of 3.51 μW/cm2 under temperature conditions representative of wearable use (T<inf>skin</inf> of 32 °C and T<inf>ambient</inf> of 26 °C). The harvested energy was then stored using a power management circuit and capacitor. This stored energy was successfully used to power a Bluetooth Low Energy (BLE) sensing module, enabling stable wireless transmission driven entirely by body heat. These results highlight the practical potential of integrating passive radiative cooling into flexible thermoelectric systems, paving the way for high-performance, battery-free wearable electronics and autonomous IoT applications.
1

Rudradawong, Chalermpol

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