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    Simultaneous Seebeck coefficient and electrical conductivity enhancement of GeSbTe films via Sn addition
    (2022-06-15)
    Khwansungnoen, Phalakorn
    ;
    Daichakomphu, Noppanut
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    ; ;
    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/cmK<sup>2</sup> 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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    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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    Item type:Publication,
    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
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    ;
    Nuthongkum, Pilaipon
    ;
    Pluengphon, Prayoonsak
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    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%.