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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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Understanding the effect of sputtering pressures on the thermoelectric properties of GeTe films
(2022-02-10)
Daichakomphu, Noppanut
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Abbas, Suman
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Chou, Ta Lei
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Chen, Li Chyong
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Chen, Kuei Hsien
In this work, we study the effect of sputtering pressures on the thermoelectric properties of GeTe films. The working pressures were differentiated from 3 to 30 mTorr, and the as-deposited films were annealed at 623 K for 10 min in Ar atmosphere. The results show that the working pressure has a significant effect on the Ge content and crystalline size. The turning trend of the Seebeck coefficient with different sputtering pressures corresponds to the Ge content. The surface morphology of annealed film will change from cracks to voids with increasing sputtering pressure. This behavior can be explained by the growth mechanisms model. The voids and relatively low crystalline size of GeTe films affect to the reduction of the electrical conductivity. In addition, the void content decreased as film thickness was increased. Therefore, controlling the working pressures in the sputtering process and film thickness is important for the thermoelectric performance of GeTe thin film. In our work, we prove that the thermoelectric properties of GeTe films could be optimized effectively by simply tuning different sputtering conditions.
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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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Effects of iron doping on the oxidation/reduction properties of delafossite CuAlO2 synthesized via a solid-state reaction
(2020-06-01)
Daichakomphu, Noppanut
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Sakulkalavek, Aparporn
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Sakdanuphab, Rachsak
CuAlO<inf>2</inf> has received a wealth of interdependent research associated with hydrogen-based catalysis in the chemical industry. Herein, Fe-doped CuAlO<inf>2</inf> is demonstrated to reduce the redox temperature for delafossite CuAlO<inf>2</inf>. Time-resolved X-ray absorption spectroscopy and hydrogen temperature-programmed reduction were used to characterize the redox properties, respectively. Delafossite CuAlO<inf>2</inf>, with and without Fe doping at 10 at% (CuAl<inf>0.9</inf>Fe<inf>0.1</inf>O<inf>2</inf>), was synthesized via a one-step solid-state reaction method. The results demonstrate that the redox temperature can be reduced by ~ 60 K for the 10 at% Fe-doped catalyst. The findings of this contribution offer a new approach to circumvent the high temperatures associated with the redox processes, and furthermore, offer a design basis for the development of new catalyst systems with enhanced regeneration abilities.
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Figure of merit improvement of delafossite CuAlO2 with the addition of Fe and graphene
(2019-11-01)
Daichakomphu, Noppanut
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Harnwunggmoung, Adul
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Chanlek, Narong
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Sakdanuphab, Rachsak
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Sakulkalavek, Aparporn
This study investigated the synthesis of delafossite CuAlO<inf>2</inf> with Fe and graphene through a solid-state reaction method. The results of X-ray diffractometry showed that graphene was insoluble in delafossite CuAlO<inf>2</inf> while Fe was substituted into Al sites, expanding the d-spacing. From X-ray photoelectron spectroscopy, graphene induced excess oxygen in the delafossite CuAlO<inf>2</inf> structure via C–O–Cu bonds and improved the electrical conductivity. In addition, the thermal conductivity was reduced due to generation of point defects, phonon-phonon Umklapp and carrier-phonon scattering. The addition of Fe and graphene in CuAlO<inf>2</inf> shows an improvement of ZT to 0.0114 at 573 K. This is attributable to its increase in charge carrier density, as well as a decrease in thermal conductivity. This study highlights the benefits of combining Fe and graphene in delafossite CuAlO<inf>2</inf> as a prospective process for attaining a high figure of merit thermoelectric materials.
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Enhanced carrier concentration of Fe doped delafossite CuAlO2 by double-effect: Divalent metal ions doping and excess oxygen
(2018-12-15)
Daichakomphu, Noppanut
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Sakdanuphab, Rachsak
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Harnwunggmoung, Adul
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Puarporn, Yingyot
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Chanlek, Narong
Bulk CuAlO<inf>2</inf> compound has been widely studied as a p-type metal oxide semiconductor material due to the simplicity in its synthesis and use of inexpensive raw materials. The Fe doping in CuAlO<inf>2</inf> has been demonstrated to enhance the electrical conductivity. An in-depth analysis of the effect of Fe doping in CuAlO<inf>2</inf> on the carrier concentration improvement was revealed. Delafossite CuAl<inf>1−x</inf>Fe<inf>x</inf>O<inf>2</inf> powders with x = 0.00, 0.05, 0.10, 0.15, 0.20 and 0.30 were synthesized by a solid-state reaction method. The X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) studies were used to measure the atomic-ion concentrations and the oxidation state of each element. The variations of carrier concentration corresponded with a ratio of Cu2+/Cu1+ in CuAlO<inf>2</inf>. We found that the increase of Cu2+/Cu1+ was caused by double effects through divalent metal ions (Fe2+) doping and excess oxygen (O<inf>2−δ</inf>) in CuAlO<inf>2</inf>. The maximum carrier concentration of 8.09 × 1017 cm−3 was obtained for the CuAlO<inf>2</inf> sample at Fe content of 10 at.%.
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Achieving thermoelectric improvement through the addition of a small amount of graphene to CuAlO2 synthesized by solid-state reaction
(2018-07-15)
Daichakomphu, Noppanut
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Sakdanuphab, Rachsak
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Harnwunggmoung, Adul
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Pinitsoontorn, Supree
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Sakulkalavek, Aparporn
In this work, delafossite CuAlO<inf>2</inf> powders with graphene (0.00–0.20 wt%) were synthesized by a solid-state reaction method. X-ray diffraction and transmission electron microscope results indicated that graphene was segregated in CuAlO<inf>2</inf> as a split phase, such as composite material. A little addition of graphene content reduces the thermal conductivity and increases the carrier concentration because the graphene generates many point defects and aided carrier-phonon scattering. The CuAlO<inf>2</inf> with graphene content of 0.05 wt% shows the maximum electrical conductivity of 470 S/m at 700 K. In addition, the maximum value for ZT of 0.0045 was recorded at 575 K with the graphene/CuAlO<inf>2</inf> composite (0.05 wt%). Therefore, in brief, this study has highlighted the benefits of combining delafossite CuAlO<inf>2</inf> with a small amount of graphene as a potential route for achieving highly efficient thermoelectric materials.

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