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Improving the photo-thermoelectric performance of CuAlO2 via doping with Bi
(2021-12-01)
Daichakomphu, Noppanut
;
Klongratog, Bhanupol
;
Rodpun, Phumin
;
Pluengphon, Prayoonsak
;
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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Figure of merit improvement of delafossite CuAlO2 with the addition of Fe and graphene
(2019-11-01)
Daichakomphu, Noppanut
;
Harnwunggmoung, Adul
;
Chanlek, Narong
;
Sakdanuphab, Rachsak
;
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
;
Harnwunggmoung, Adul
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Puarporn, Yingyot
;
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
;
Sakdanuphab, Rachsak
;
Harnwunggmoung, Adul
;
Pinitsoontorn, Supree
;
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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