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    Reinvestigation thermoelectric properties of CuAlO2
    (2014-01-01) ;
    Kosalwat, Wattana
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    Jindajitawat, Phumin
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    Bulk CuAlO2 delafossite has been synthesized by solid state reaction to reinvestigate the thermoelectric properties. The electrical conductivity, Seebeck coefficient and thermal conductivity were measured in a high temperature range of 300 to 960 K. The result of positive sign of Seebeck coefficient confirms p-type nature of CuAlO2 compund. The results of bulk sample for Seebeck coefficient, the electrical conductivity and thermal conductivity are range of 900 to 300 μV/K, of 0.01 to 2 S/cm, and of 3.5 W/mK to 1.5 W/mK. The maximum ZT value of bulk sample is 0.017 at a 960 K. These results can be concluded that the bulk CuAlO2 by solid state state displays thermoelelctric material.
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    Preparation, characterization and finite element computation of Cu(Al 1/2Fe1/2)O2 Delafossite-oxide themoelectric generator module
    (2014-09-02) ;
    Jindajitawat, Phumin
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    Naenkieng, Daengdesh
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    Boonyopakorn, Narongchai
    The CuAl<inf>1/2</inf>Fe<inf>1/2</inf>O<inf>2</inf> delafossite oxide has been synthesized by solid state reaction method for studying thermoelectric properties and measuring thermoelectric generator output electric power. The Finite Element technique was used to compute the output voltage of thermoelectric generator in applying temperature difference on a single bar and a module model with compared to the measurement results. The measurement results of positive sign Seebeck coefficient confirm the p-type conductor of the sample. The properties of Seebeck coefficient, electrical conductivity, and thermal conductivity are range from 260 to 310V/K, from 7 to16 S/cm and from 2.5 to 3.5 W/cm-K,respectively, in the temperature range of 300 to 960 K. The output voltage of the single bar in dimension 4.2 × 2.5 × 20 mm <sup>3</sup> obtained 0.5 to 3 mV on applying temperature difference from 1 to 10 K closely to the Finite Element result. The computing results of the thermoelectric single bar and module in high temperature reveal the output electric voltage of CuAl<inf>1/2</inf>Fe<inf>1/2</inf>O<inf>2</inf> oxide raises with the temperature and the number of thermoelectric leg increase. In important results, the high value of electric voltage is obtained 0.2 and 0.4 V for the single bar and the module at 950 K. © 2014 Taylor & Francis Group, LLC.
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    Electrical and optical properties of p-type CuFe1-xSn xO2 (x = 0.03, 0.05) delafossite-oxide
    (2013-01-14) ; ; ;
    Kongtaweelert, Samart
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    Thanachayanont, Chanchana
    The CuFe<inf>1-x</inf>Sn<inf>x</inf>O<inf>2</inf> (x = 0.03, 0.05) delafossite samples have been synthesized by a solid-state reaction to investigate electrical and optical properties of the transparent conducting oxide materials. Crystal structure was characterized by XRD. The electrical conductivity and Seebeck coefficient were measured in the high temperature range of 300 to 960 K, while the Hall coefficient, XPS, and UV-VIS-NIR spectra were analyzed at room temperature. The XRD peaks of the samples indicate the delafossite structure phase, and the XPS spectra reveal the stable Sn <sup>2+</sup>-doping state. The Seebeck and Hall coefficient display a positive sign indicating the p-type conducting oxide. The optical allowed direct gap is 3.45 eV as a visible-transparent material. The activation energies for polaron hopping between Sn<sup>2+</sup> sites and Fe<sup>3+</sup> sites of 36 and 32 meV are obtained from the samples having x = 0.03 and 0.05, respectively. The CuFe<inf>1-x</inf>Sn<inf>x</inf>O<inf>2</inf> delafossite oxide compounds, of which the Fe<sup>3+</sup> sites in the CuFeO<inf>2</inf> are substituted by the Sn<sup>2+</sup> ions, are p-type transparent conducting oxide materials. The activation energy is found to decrease with an increased in Sn content. © 2013 American Institute of Physics.
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    Effect of Strong Correlation of Mg2+-doped into Cr3+ Sites of CuCrO2 on Thermoelectric Properties
    (2015-09-02) ;
    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 Mg<sup>2+</sup>-substituted into Cr<sup>3+</sup> 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 Mg<sup>2+</sup>, Cu<sup>1+</sup>, Cr<sup>3+</sup> and Cr<sup>4+</sup> ion states. The Mg<sup>2+</sup> induced mixed-valance Cr<sup>3+</sup>/Cr<sup>4+</sup> 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 Mg<sup>2+</sup>-substituted for Cr<sup>3+</sup> of CuCrO2 delafossite enhance the thermoelectric properties. © 2015
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    Thermoelectric properties of Sn2+-substituted CuFeO2 delafossite-oxide
    (2013-10-29) ;
    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 Sn<sup>2+</sup>-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<sup>+2</sup> state as confirming the Sn-doped CuFeO<inf>2</inf> playing p-type conductor. The Sn<sup>2+</sup>-substituted supports the mixed valency Fe<sup>3+</sup>/Fe<sup>4+</sup> 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<sup>-4</sup> W/mK<sup>2</sup> 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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    High temperature thermoelectric properties of delafossite CuBO2
    (2014-01-01) ;
    Jindajitawat, Phumin
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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<sup>-5</sup> to 5.3 × 10<sup>-5</sup> W/m-K<sup>2</sup> with the same temperature. The maximum PF and ZT is 5.3 × 10<sup>-5</sup> W/m-K<sup>2</sup> 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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    Temperature-dependent electrical transport, Hall effect, and Seebeck properties of bulk chemically reduced graphene oxide with bipolar charge carrier materials
    (2023-03-01)
    Maneesai, Keerati
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    Silakaew, Kanyapak
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    Khammahong, Sunisar
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    The temperature-dependent electrical transport, Hall effect, and Seebeck properties of bulk-reduced graphene oxide (rGO) prepared by a chemical reduction process were investigated in a temperature range of 310-475 K. The bulk rGO contained bipolar charge carriers with p-type to n-type switching at a temperature of 420 K. The materials illustrated a p-type characteristic in the temperature range of 310-420 K and n-type characteristic in the temperature range of 420-475 K. The charge transport mechanism was that of the graphene-derived 2D material in the p-type regime and governed by polaronic charge carriers.
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    Item type:Publication,
    Preface
    (2021-09-20)
    Thammavintorn, Preecha
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    Limkaisang, Viroj
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    Charoenprakdee, Anek
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    Seetawan, Tosawat
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    Kimura, Kaoru