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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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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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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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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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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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Influence of Na doping on the thermoelectric properties of CuAlO2 delafossite
(2014-01-01)
Wongcharoen, Ngamnit
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Gaewdang, Thitinai
The polycrystalline Na-doped CuAlO<inf>2</inf> ceramics were obtained by solid state reaction method. The mixture of high purity grade of CuO, Al<inf>2</inf>O<inf>3</inf> and NaNO<inf>3</inf>·6H<inf>2</inf>O powders was ground and then pressed by using uniaxial pressure. The obtained pellet was sintered in air at 1,423 K for 24 h. XRD patterns showed the crystal structure of the as-sintered Cu<inf>1-x</inf>Na<inf>x</inf>AlO<inf>2</inf> (0≤x≤0.05) belonging to rhombohedral, space group R3m along with the CuO and CuAl<inf>2</inf>O<inf>4</inf> phases. The minimum resistivity value around 4.48x102 Ω ·cm and maximum hole concentration around 2.04x1016 cm-3 were observed for x=0.03 at room temperature. The properties of Seebeck coefficient and electrical resistivity were measured in the high temperature ranging 300 to 700 K. The results of electrical resistivity, Seebeck coefficient and power factor values decrease with increasing Na content. The calculated activation energy of conductivity (in the range of 160-250 meV) is larger than that of thermopower (in the range of 26-83 meV) which suggests that the conduction mechanism may be determined as a small polaron hopping type. © (2014) Trans Tech Publications, Switzerland.
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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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Structural and thermoelectric properties of zn-doped cuprous aluminate delafossite
(2013-10-04)
Wongcharoen, Ngamnit
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Gaewdang, Thitinai
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Wongcharoen, Tiparatana
The polycrystalline Zn-doped CuAlO<inf>2</inf> ceramics were obtained by solid state reaction method. The mixture of high purity grade of CuO, Al<inf>2</inf>O<inf>3</inf> and Zn(CH<inf>3</inf>COO) <inf>2</inf>{dot operator}2H<inf>2</inf>O powders was ground and then pressed by using uniaxial pressure. The obtained pellet was sintered in air at 1,150 °C for 24 h. XRD patterns showed the crystal structure of the as-sintered CuAl<inf>1-x</inf>Zn<inf>x</inf>O<inf>2</inf> (0≤x≤0.05) belonging to rhombohedral, space group R3m along with the CuO and CuAl2O4 phases. From SEM micrographs, the grain size slightly decreases when the amount of Zn in CuAl<inf>1-x</inf>Zn<inf>x</inf>O<inf>2</inf> samples increases. Hall mobility and hole concentration of the as-sintered samples were obtained from Hall effect measurements in van der Pauw configuration at room temperature. The electrical resistivity measurements as a function of temperature were performed. The variation of Seebeck coefficient and power factor as a function of temperature was also investigated. In the present study, the Zndoped CuAlO<inf>2</inf> ceramics probably have advantages for use in high temperature thermoelectric devices. © (2013)Trans Tech Publications,Switzerland.
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Theoretical study of electronic structure and thermoelectric properties of doped CuAlO 2
(2011-05-01)
Poopanya, P.
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Yangthaisong, A.
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Rattanapun, C.
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Wichainchai, A.
The doping level dependence of thermoelectric properties of delafossite CuAlO <inf>2</inf> has been investigated in the constant scattering time (τ) approximation, starting from the first principles of electronic structure. In particular, the lattice parameters and the energy band structure were calculated using the total energy plane-wave pseudopotential method. It was found that the lattice parameters of CuAlO <inf>2</inf> are a = 2.802 Å and c = 16.704 Å, and the internal parameter is u = 0.1097. CuAlO <inf>2</inf> has an indirect band gap of 2.17 eV and a direct gap of 3.31 eV. The calculated energy band structures were then used to calculate the electrical transport coefficients of CuAlO <inf>2</inf>. By considering the effects of doping level and temperature, it was found that the Seebeck coefficient S(T) increases with increasing acceptor doping (A <inf>d</inf>) level. The values of S(T) in our experiments correspond to an A <inf>d</inf> level at 0.262 eV, which is identified as the Fermi level of CuAlO <inf>2</inf>. Based on our experimental Seebeck coefficient and the electrical conductivity, the constant relaxation time is estimated to be 1 × 10 -16 s. The power factor is large for a low A <inf>d</inf> level and increases with temperature. It is suggested that delafossite CuAlO <inf>2</inf> can be considered as a promising thermoelectric oxide material at high doping and high temperature. © 2010 TMS.

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