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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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Effects of Pd substitution on the thermoelectric and electronic properties of delafossite Cu1-xPdxFeO2 (x=0.01, 0.03 and 0.05)
(2014-07-01)
Ruttanapun, Chesta
Cu<inf>(1-x)</inf>Pd<inf>(x)</inf>FeO<inf>2</inf> (x=0.01, 0.03 and 005) delafossite was prepared by solid state reactions and was calcined/sintered at 1050 °C. The effect of Pd2+ substitution for the Cu1+ sites on the thermoelectric and electronic properties of Cu <inf>(1-x)</inf>Pd<inf>(x)</inf>FeO<inf>2</inf> were investigated. The crystal structure, oxygen decomposition, thermoelectric and electronic properties were characterized by X-ray diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy (XPS), Seebeck coefficient, electrical conductivity and thermal conductivity measurements. The characterization showed that Cu <inf>(1-x)</inf>Pd<inf>(x)</inf>FeO<inf>2</inf> formed a hexagonal delafossite structure with R3-m symmetry. The existence of Pd2+, Cu1+, Cu2+, Fe3+, Fe4+ and O was revealed from the XPS results. Confirmation of Pd2+ substitution for the Cu 1+ sites occurred by increasing the c-axis in the lattice parameter with a Pd content. The O content intercalated at the center of the triangular Cu acted as a support to produce Cu2+ ions and was reduced with an increasing Pd content. The mixed valencies of Cu1+/Cu2+ and Cu1+/Pd2+ in the Cu layer changed the electrical conductivity and the Fe3+/Fe4+ mixed valencies in the FeO<inf>6</inf> layer caused the Seebeck coefficient to increase. Both the electrical conductivity and Seebeck coefficient for Pd contents of x=0.01 and 0.03 were higher than that of non-doped CuFeO<inf>2</inf>. The low thermal conductivity of Cu<inf>(1-x)</inf>Pd<inf>(x)</inf>FeO<inf>2</inf> resulted from the substitution of Pd, which has a large atomic mass, into structure. The Jonker plot indicated that the electronic properties displayed a degenerate density of states and that Cu<inf>(1-x)</inf>Pd<inf>(x)</inf>FeO<inf>2</inf> was a semiconductor. A high ZT value of 0.055 was obtained for a Pd content of 0.03 at 950 K. The Pd2+ substitution for the Cu1+ sites influenced the thermoelectric and electronic properties of the delafossite Cu<inf>(1-x)</inf>Pd<inf>(x)</inf>FeO<inf>2</inf> samples. © 2014 Elsevier Inc.
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High temperature thermoelectric properties of delafossite CuBO2
(2014-01-01)
Ruttanapun, Chesta
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Jindajitawat, Phumin
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Buranasiri, Prathan
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Thowladda, Warawoot
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Neeyakorn, Worakarn
CuBO<inf>2</inf> is prepared by a solid-state reaction method to investigate thermoelectric properties in high temperature. The XRD result confirms the CuBO<inf>2</inf> compound existing in this method. The Seebeck reveals the compound displays p-type thermoelectric material. The experimental results of electrical resistivity exhibited results of 0.004 S/cm to 0.038 S/cm with the temperature range of 650 to 830 K. The Seebeck value is in the range of 450 μV/K to 950 μV/K, and the thermal conductivity is in the range of 1.4 × 10-5 to 5.3 × 10-5 W/m-K2 with the same temperature. The maximum PF and ZT is 5.3 × 10-5 W/m-K2 and 0.0016, respectively, at 960 K. This work demonstrates that the CuBO<inf>2</inf> delafossite-oxide compound displays the p-type thermoelectric materials. © 2014 IEEE.
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Method of high active preparation and electrical properties of CuFeO2 delafossite-type
(2014-01-01)
Rudradawong, Chalermpol
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Wichainchai, Aree
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Sakulkalavek, Aparporn
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Hongaromkid, Yuttana
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Ruttanapun, Chesta
In this paper, the CuFeO<inf>2</inf> compound were prepared by classical solid state reaction (CSSR) and direct powder dissolved solution (DPDS) method from starting material metal oxides and metal powders. Preparation of two methods shows that, direct powder dissolved solution faster recover phases than classical solid state reaction method. The fastest method gets from starting materials Cu and Fe metal powders, the electrical conductivity, Seebeck coefficient, carrier concentration and mobility are 10. 68 S/cm, 244. 59 μV/K, 12. 86×1016 cm-3 and 494. 96 cm2/V. s, respectively. In addition, each CuFeO<inf>2</inf> compounds were investigated on crystal structure and electrical properties. From XRD and SEM results, all samples have a crystal structure delafossitetype (R3m) and a large grain boundary more than 15 μm by electrical conductivity corresponds to grain boundary and lattice parameter: a increases. Within this paper, from above results exhibit that preparation CuFeO<inf>2</inf> from Cu and Fe by direct powder dissolved solution method most appropriate for thermoelectric oxide materials due to high active for preparation else high lattice strain and high power factor are 0. 00052 and 0. 64×10-4 W/mK2, respectively. © (2014) Trans Tech Publications, Switzerland.
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Thermoelectric properties of Cu1-xPtxFeO2 (0.0 ≤ x ≤ 0.05) delafossite-type transition oxide
(2011-03-31)
Ruttanapun, Chesta
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Wichainchai, Aree
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Prachamon, Wutthisak
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Yangthaisong, Anucha
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Charoenphakdee, Anek
The samples of Cu<inf>1-x</inf>Pt<inf>x</inf>FeO<inf>2</inf> (0 ≤ x ≤ 0.05) delafossite were synthesized by solid state reaction method for studying thermoelectric properties. The properties of Seebeck coefficient, electrical conductivity and thermal conductivity were measured in the high temperature ranging from 300 to 960 K. The results of Seebeck coefficient, electrical conductivity and power factor were increased with increasing Pt substitution and temperature. The thermal conductivity was decreased from 5.8 to 3.5 W/mK with increasing the temperature from 300 to 960 K. An important results, the highest value of power factor and ZT is 2.0 × 10-4 W/mK2 and 0.05, respectively, for x = 0.05 at 960 K. © 2011 Elsevier B.V. All rights reserved.

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