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Author: search.filters.author.Muthitamongkol, Pennapa

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    Effect of Ag mixing in thermoelectric Ge2Sb2Te5 thin films
    (2019-01-01)
    Vora-ud, Athorn
    ;
    Horprathum, Mati
    ;
    Kumar, Manish
    ;
    Muthitamongkol, Pennapa
    ;
    Chananonnawathorn, Chanunthorn
    Ag-added Ge<inf>2</inf>Sb<inf>2</inf>Te<inf>5</inf> thin films were prepared by a pulsed-DC co-magnetron sputtering process using Ge<inf>2</inf>Sb<inf>2</inf>Te<inf>5</inf> and Ag targets. The effect of variation in Ag content through variable power on Ag target was studied on the microstructural and thermoelectric properties of as-deposited and fast annealed thin films at 400 °C in a vacuum. It is found that Ag addition induces enhancement in conductivity. When the power on Ag target is exceeded to a critical power, Ag<inf>8</inf>GeTe<inf>6</inf> phase formation occurs mixed with Ge<inf>2</inf>Sb<inf>2</inf>Te<inf>5</inf> cubic structure which limits the thermoelectric performance. Best conditions provide the films having a lowest electrical resistivity as 0.98 × 10<sup>−4</sup> Ω cm and the maximum power factor as 5.83 × 10<sup>−3</sup> W m<sup>−1</sup> K<sup>−2</sup>.
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    Effect of Strong Correlation of Mg2+-doped into Cr3+ Sites of CuCrO2 on Thermoelectric Properties
    (2015-09-02)
    Ruttanapun, Chesta
    ;
    Charoenphakdee, Anek
    ;
    Nisoa, Mudtorlep
    ;
    Muthitamongkol, Pennapa
    ;
    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