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Grain boundary, electrical transport and thermoelectric properties of the ultra-high rGO amount of C12A7-rGO composites
(2024-04-30)
Maneesai, Keerati
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Thongkam, Montree
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Sriwong, Chaval
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Ruttanapun, Chesta
The Ca<inf>12</inf>Al<inf>14</inf>O<inf>33</inf> ceramic (C12A7) and reduced graphene oxide (rGO) composite which an ultra-high amount (i.e., 40, 50, 60, and 70 wt%) of rGO (ultra-high amount C12A7/rGO composite) were synthesized by a solid-state reaction process. After the hydraulic press, the heat treatment in the temperature range of 773 K under the argon environment had been performed with the composite pellets for 30 min. XRD results of the C12A7 and all the ultra-high amount C12A7/rGO composites indicated a pure phase of C12A7 ceramic. Raman spectra confirmed the existence of rGO content in all the ultra-high amount C12A7/rGO composites. Raman peaks also suggested reduction of the free O<inf>2</inf>2− and O<inf>2</inf>− ions from the framework of the ultra-high amount C12A7/rGO composites. SEM image presented the homogeneous grain boundary interface after the heat treatment at 773 K of the C12A7 wrapped by the rGO sheet, the agglomerated rGO sheet, and the rough interface stack of rGO sheets. UV-VIS spectroscopy presented the absorption behavior, direct energy gap, and indirect energy gap modifications of the ultra-high amount C12A7/rGO composites. Electrical conductivity of the ultra-high amount C12A7/rGO composites illustrated larger than 108 times improvement with temperature independence. Range of −5 to −17 μV/K, temperature dependence, and increased with rGO content increasing Seebeck coefficient were reported. Thermal conductivity of the ultra-high amount C12A7/rGO composites was increased with the rGO content increasing. Both the Power factor (PF) and the figure of merit (ZT) of the ultra-high amount C12A7/rGO composites were temperature dependent and were increased with the rGO content increasing, within the range of 0.4 μW/m.K2 of PF and the range of 3x10−4 of ZT, respectively. These experimental results verified grain boundary, modified energy band, electrical transport properties and thermoelectric properties of C12A7/rGO composites loading with ultra-high content rGO
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Effect of Strong Correlation of Mg2+-doped into Cr3+ Sites of CuCrO2 on Thermoelectric Properties
(2015-09-02)
Ruttanapun, Chesta
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Charoenphakdee, Anek
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Nisoa, Mudtorlep
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Muthitamongkol, Pennapa
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Thanachayanont, Chanchana
This study aims to investigate the strong correlation effect of spin and charge carriers for the Mg2+-substituted into Cr3+ sites of CuCrO2 delafossite on thermoelectric properties. The CuCr0.98Mg0.02O2 sample was synthesized by a solid state reaction. The starting powder CuO, Cr2O3 and MgO were ball milled with poly vinyl alcohol solution for 24 h. The ball milled powder was pressed and sintered in air atmosphere at temperature 1050 C for 6 h. The crystal structure was characterized by XRD, TGA, XPS and the thermoelectric properties were measured at high temperature. The XRD displayed peaks of the pure phase CuCrO2 structure as hexagonal delafossite-type structure space group: Rm. The Seebeck coefficient of the samples displayed positive sign as p-type (hole) conductor. The XPS results displayed Mg2+, Cu1+, Cr3+ and Cr4+ ion states. The Mg2+ induced mixed-valance Cr3+/Cr4+ states resulting in enhanced Seebeck coefficient due to a strong correlation of the spin-entropy. The experimental results of Seebeck value were close to calculated results by the extended Heikes formula confirming of the strong correlation effect. In addition, the Mg-doped CuCrO2 resulted in increased electrical conductivity and reduced thermal conductivity with increasing temperature. These indicate that the Mg2+-substituted for Cr3+ of CuCrO2 delafossite enhance the thermoelectric properties. © 2015
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Thermoelectric properties of Sn2+-substituted CuFeO2 delafossite-oxide
(2013-10-29)
Ruttanapun, Chesta
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Jindajitawat, Phumin
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Thowladda, Warawoot
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Neeyakorn, Worakarn
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Thanachayanont, Chanchana
This study aims to investigate the effect of the Sn2+-substituted into the CuFeO<inf>2</inf> delafossite on thermoelectric properties in the Sn content of x = 0.03, 0.05. The CuFe<inf>1-x</inf>Sn<inf>x</inf>O<inf>2</inf> samples were synthesized by solid state reaction. The crystal structure was characterized by XRD, TGA, XPS and the thermoelectric properties were measured in the range of 300 to 960 K. The Seebeck coefficient display positive sign in all temperature range and the XPS show the stable Sn+2 state as confirming the Sn-doped CuFeO<inf>2</inf> playing p-type conductor. The Sn2+-substituted supports the mixed valency Fe3+/Fe4+ state in transition octahedral oxide of FeO<inf>6</inf> layer enhancing Seebeck coefficient. The high Seebeck are appeared in content of x=0.03 which are 280 to 340 μV/K in the range of 300 to 800 K. The experimental Seebeck corresponds to the prediction formula at high temperature. Totally, the maximum Power Factor is 2.30×10-4 W/mK2 occurring in the CuFe<inf>0.95</inf>Sn<inf>0.05</inf>O<inf>2</inf> at 860 K which is higher than that value of the undoped-CuFeO<inf>2</inf> in 4 times. These support that the Sn-substituted CuFeO<inf>2</inf> delafossite enhancing thermoelectric properties. © (2013) Trans Tech Publications, Switzerland.
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Microwave-assisted solution combustion synthesis and characterization of thermoelectric Ca3Co2O6 powders
(2013-10-29)
Kahatta, Sagulthai
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Chaiyo, Nopsiri
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Ruttanapun, Chesta
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Techitdheera, Wicharn
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Pecharapa, Wisanu
The microwave-assisted solution combustion synthesis was applied to the initial synthesizing of Ca<inf>3</inf>Co<inf>2</inf>O<inf>6</inf> powder using glycine as a fuel and nitrate as an oxidant. The assynthesized powders were calcined at 700-1,000°C for 4h. Product characterization was performed using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and Scanning electron microscope (SEM). The fuel-to-oxidizer molar ratio was found to affect the combustion reaction and character of the powder obtained. The phase composition of powder after calcination at various temperatures has shown that the formation of Ca<inf>3</inf>Co<inf>2</inf>O<inf>6</inf> occurs directly. The calcined powder possesses a rhombohedral crystal structure with an X-ray diffraction pattern that could be matched with the Ca<inf>3</inf>Co<inf>2</inf>O<inf>6</inf>JCPDS: 89-0629. This method is a simple way of synthesizing fine Ca<inf>3</inf>Co<inf>2</inf>O<inf>6</inf> powder with a low calcination temperature. © (2013) 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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