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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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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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Power factor improvement of delafossite CuAlO2 by liquid-phase sintering with Ag2O addition
(2016-12-01)
Sakulkalavek, Aparporn
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Sakdanuphab, Rachsak
Thermoelectric delafossite (CuAlO<inf>2</inf>)<inf>1−x</inf>(Ag<inf>2</inf>O)<inf>x</inf> with 0<x<0.06 is prepared at three different sintering temperatures, 1323 K, 1373 K, and 1473 K. The samples are obtained from a mixture of CuO, Al<inf>2</inf>O<inf>3</inf>, and additive Ag<inf>2</inf>O powders. The mixture is ground and then pressed with uniaxial pressure into pellets. Differential scanning calorimetry and X-ray diffraction spectroscopy show that the sintering temperature to synthesize delafossite CuAlO<inf>2</inf> with Ag<inf>2</inf>O addition is below 1473 K. X-ray diffraction patterns show the major phase of delafossite 3R-CuAlO<inf>2</inf> along with a trace amount of 2H-CuAlO<inf>2</inf>. A small amount of the Ag phase is present in the samples depending on the amount of Ag<inf>2</inf>O addition and sintering temperature. Energy dispersive spectroscopy and backscattered electron image analyses show that the Ag phase is segregated around the grain boundary. Liquid-phase sintering is used to explain the growth mechanism. The CuAlO<inf>2</inf> samples with Ag<inf>2</inf>O addition obviously exhibit enhanced bulk density, grain size, and electrical conductivity. The highest power factor (PF), obtained by CuAlO<inf>2</inf> with 2 at% of Ag<inf>2</inf>O sintered at 1373 K, is 8.23×10−5 W/(m K2) at 873 K. Hence, our findings show an improvement for delafossite CuAlO<inf>2</inf> by Ag<inf>2</inf>O addition.
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Figures of merit of low-cost CuAl0.9Fe0.1O2 thermoelectric material prepared at different solid state reaction sintering temperatures
(2015-01-01)
Sakulkalavek, Aparporn
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Thonglamul, Rungnapa
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Sakdanuphab, Rachsak
In this study, we investigated a CuAl<inf>0.9</inf>Fe<inf>0.1</inf>O<inf>2</inf> compound prepared at two different sintering temperatures in order to find out the effects of sintering temperature on the compound's figure of merit of thermoelectric properties. The thermoelectric CuAl<inf>0.9</inf>Fe<inf>0.1</inf>O<inf>2</inf> compounds were prepared from high purity grade Cu<inf>2</inf>O, Al<inf>2</inf>O<inf>3</inf> and Fe<inf>2</inf>O<inf>3</inf> powders. The mixture of these powders were ground and then pressed with uniaxial pressure into pellets. The pellets obtained were sintered in the air at 1423K and 1473K. X-ray diffraction (XRD) patterns showed a single phase of CuAl<inf>0.9</inf>Fe<inf>0.1</inf>O<inf>2</inf> with rhombohedral structure, R3¯m, along with a trace of CuO second phase. Moreover, the XRD peaks of the sample sintered at 1423K indicated that more Fe3+ atoms replaced Al3+ atoms in this sample than they did in the sample sintered at 1473K. The average grain size of the CuAl<inf>0.9</inf>Fe<inf>0.1</inf>O<inf>2</inf> compound prepared increased with increasing sintering temperature, whereas its mean pore size and porosity decreased with increasing sintering temperature. The dispersed small pores markedly decreased the thermal conductivity of the compound, while the Fe3+ substitution of Al3+ increased its electrical conductivity. The highest figure of merit (ZT) found was 0.021 at 973K in the CuAl<inf>0.9</inf>Fe<inf>0.1</inf>O<inf>2</inf> sample sintered at 1423K. Our findings show that this low-cost material with a reasonable figure of merit is a good candidate for thermoelectric applications at high-temperature.

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