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    Energy-saving synthesis and β-phase enhancement of Cu2Se thermoelectric materials via the microwave hybrid heating technique
    (2021-10-25) ; ; ;
    Harnwunggmoung, Adul
    ;
    Horprathum, Mati
    Thermoelectric generators harvest energy from waste heat and convert it to electricity. β-Cu<inf>2</inf>Se is a candidate for them due to its outstanding thermoelectric properties and its environmentally friendly component elements. A microwave hybrid heating (MHH) method was used for the fast synthesis and enhancement of β-Cu<inf>2</inf>Se materials. The effects of the MHH reaction time on the phase microstructure and thermoelectric properties of the Cu<inf>2</inf>Se material were investigated, and the MHH method was compared with the conventional heating method. The X-ray diffraction patterns of samples, synthesized via the MHH method, showed monoclinic- (α) and cubic- (β) Cu<inf>2</inf>Se crystalline structures, whereas a single monoclinic-(α) structure was identified in a sample, synthesized via a conventional heating method. In addition, the β-Cu<inf>2</inf>Se phase was enhanced with increased MHH reaction time. The carrier concentration increased with β-Cu<inf>2</inf>Se content, which increased electrical conductivity and decreased the Seebeck coefficient. The Cu<sup>+</sup> ions in the β-Cu<inf>2</inf>Se phase led to the reduced thermal conductivity. A low thermal conductivity of 0.86 W m<sup>−1</sup> K<sup>−1</sup> and a maximum dimensionless figure of merit of 0.32 at 523 K were realized for 10 min MHH sample. Finally, MHH showed very low energy consumption and saved time, which are essential for industrialization.
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    Improving the thermoelectric properties of thick Sb2Te3 film via Cu doping and annealing deposited by DC magnetron sputtering using a mosaic target
    (2021-11-01)
    Theekhasuk, Nattharika
    ;
    ;
    Nuthongkum, Pilaipon
    ;
    Pluengphon, Prayoonsak
    ;
    Harnwunggmoung, Adul
    Thick Cu-doped Sb<inf>2</inf>Te<inf>3</inf> films were deposited on flexible substrate by DC magnetron sputtering from a mosaic Cu–Sb<inf>2</inf>Te<inf>3</inf> target. The Cu-doped Sb<inf>2</inf>Te<inf>3</inf> films were vacuum annealed to improve their thermoelectric properties. Density functional theory was used to clarify the internal mechanism of the Cu doped into the Sb<inf>2</inf>Te<inf>3</inf> system. The results showed that Cu substitution on a Sb site induced electronic states or impurity peaks of Sb<inf>2</inf>Te<inf>3</inf> at a valence band maximum. The carrier concentration of the Cu-doped Sb<inf>2</inf>Te<inf>3</inf> films increased as the Cu-doped concentration increased. However, the crystallite size and Seebeck coefficient of the Cu-doped Sb<inf>2</inf>Te<inf>3</inf> films decreased as the Cu-doped concentration increased. Post-annealing treatment improved the microstructure and thermoelectric properties of the Cu-doped Sb<inf>2</inf>Te<inf>3</inf> films. The maximum electrical conductivity and power factor values of 754.20 S/cm at 50 °C and 1.56 10<sup>−3</sup> W/mK<sup>2</sup> at 100 °C were obtained in the annealed film with a Cu-doped concentration of 3 at%.
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    Item type:Publication,
    Enhancement of thermoelectric properties in rapidly synthesised β-Cu2Se using optimized Cu content and microwave hybrid heating
    (2024-01-15) ; ;
    Gobpant, Jakrit
    ;
    Harnwunggmoung, Adul
    ;
    To our knowledge, this is the first study to successfully synthesise high-temperature-phase copper selenide (β-Cu<inf>2</inf>Se) at room temperature using rapid microwave hybrid heating (MHH). Controlling the starting Cu/Se ratio is the critical parameter for adjusting the content of α- and β-phases in the as-synthesised sample. The relatively low Cu composition causes impurities to form in the Cu<inf>3</inf>Se<inf>2</inf> phase, deteriorating the thermoelectric (TE) properties of the Cu<inf>2</inf>Se material. The β phase formation at room temperature promotes electrical conductivity. The thermal conductivities of the Cu<inf>2.0</inf>Se samples were 0.5–0.8 Wm<sup>−1</sup>K<sup>−1</sup> at 303–673 K. A strong electronic-phonon interaction may potentially couple electronic thermal conductivity (κ<inf>e</inf>) and lattice thermal conductivity (κ<inf>L</inf>), resulting in incomplete separability of κ<inf>L</inf> and κ<inf>e</inf> in the β-Cu<inf>2.0</inf>Se sample. The Cu<inf>2.0</inf>Se exhibited a ZT value of 0.65 at 523 K because of its considerably lowered thermal conductivity.