• Korean Journal of Materials Research
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• v.7 no.1
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• pp.40-49
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• 1997

$Bi_{2}(Te_{0.9}Se_{0.1})_{3}$ thermoelectric matcrials havc 11et:n fahricxted hy mechanical alloying and hot pressing methods. Microstructure and thermoelectric properties of the hot 11resseii $Bi_{2}(Te_{0.9}Se_{0.1})_{3}$ have been investigated Lvith variations of hot pressing temperature and dopmt atltiition Formation of $Bi_{2}(Te_{0.9}Se_{0.1})_{3}$ alloy powders was completed by mechanical alloying of the as-mixed Ri. Te, arid Sc grmules of ~3.6mm size for 3 hours at ball-to-material weight ratio of 5 : 1. Figure of merit of $Bi_{2}(Te_{0.9}Se_{0.1})_{3}$ was markedly incrcwieti hy hot pressing at temperatures above $450^{\circ}C$, and value of $1.9{\times}10^{-3}/K$ was obtained for the specimen hot pressed at $550^{\circ}C$. With addition of 0.015 wt% Ri as acceptor dopant, figure of merit ol $Bi_{2}(Te_{0.9}Se_{0.1})_{3}$ hot pressed $550^{\circ}C$$2.1{\times}10^{-3}/K$.

• Composites Research
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• v.29 no.4
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• pp.156-160
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• 2016

Glassy carbon can be utilized in a variety of harsh environment due to exceptional thermal stability and chemically impermeability along with scalability and low electrical resistance. In this work, we studied effects of electron(e)-beam irradiation on thermoelectric properties of the glassy carbon film. E-beam irradiation triggered local crystallization and/or amorphization of glassy carbon thin films, which was determined by a Raman spectroscopy. The structural change by e-beam irradiation leads to the change in the doping level of the glassy carbon, which can be inferred from the change of a Seebeck coefficient and an electric conductivity. The optimal power factor we obtained for the irradiated glassy carbon film was ~200% higher than that of the non-irradiated sample.

• Korean Journal of Materials Research
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• v.25 no.2
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• pp.68-74
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• 2015

The porous $Mg_3Sb_2$ based compounds with 60~70% of relative density were prepared by powder compaction at room temperature and reactive liquid phase sintering at 1023 K for 4hrs. The stoichiometric $Mg_3Sb_2$ compounds were synthesized from elemental Sb and Mg powder in the mixing range of 61~63 at% Mg. The increased scattering effect due to the micro-pores reduced the mobility of the charge carrier and the phonon, which caused the electrical conductivity and the thermal conductivity to decrease, respectively. But the scattering effect was greater for the electrical conductivity than for the thermal conductivity. Excess Mg alloyed in the $Mg_3Sb_2$ compounds decreased the electrical conductivity, but had no effect on the thermal conductivity. On the other hand, the large increase of the Seebeck coefficient was the result of a decrease in the charge carrier density due to the excess Mg. Dimensionless figure of merit of the porous $Mg_3Sb_2$ compound reached a maximum value of 0.28 at 61 at% Mg. The obtained value was similar to that of $Mg_3Sb_2$ compounds having little pores.

• Korean Journal of Materials Research
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• v.8 no.3
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• pp.245-251
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• 1998

Bi-doped n-type PbTe thermoeletric materials were fabricated by mechanical alloying and hot pressing. The intering characteristics and thermoelectric properties of the hot- pressed PbTe were characterized and compared with the properties of the specimens prepared by meltingigrinding method. The hot-pressed PbTe specimens fabricated by mechanical alloying exhibited more negative Seebeck coefficient, higher electrical resistivity and lower thermal conductivity. compared to ones prepared by meltingigrinding. The maximum figure-of-merit increased and the temperature for the maximum figure-of-merit shifted to lower temperature for the specimens fabricated by mechanical alloying. When hot pressed at $650^{\circ}C$, 0.3 wt% Bi-doped PbTe fabricated by mechanical alloying and meltingjgrinding exhibited maximum figure-of-merits of $1.33\times10^{-3}/K$ at $200^{\circ}C$ and $1.07\times10^{-3}/K$ at $400^{\circ}C$ respectively.

• Journal of the Microelectronics and Packaging Society
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• v.20 no.1
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• pp.15-19
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• 2013

The n-type $Bi_2(Te_{0.9}Se_{0.1})_3$ powders, which were fabricated by melting/grinding method and dispersed with 0.5 vol% $TiO_2$ nanopowders, were hot-pressed in order to investigate the effects of $TiO_2$ dispersion on the thermoelectric properties of the hot-pressed $Bi_2(Te_{0.9}Se_{0.1})_3$. Excellent thermoelectric properties such as a maximum figure-of-merit of $2.93{\times}10^{-3}/K$ and a maximum dimensionless figure-of-merit of 1.02 were obtained for the hot-pressed $Bi_2(Te_{0.9}Se_{0.1})_3$. With dispersion of 0.5 vol% $TiO_2$ nanopowders, the maximum figure-of-merit and the maximum dimensionless figure-of-merit decreased to $2.09{\times}10^{-3}/K$ and 0.68, respectively.

• Journal of the Korean Society for Heat Treatment
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• v.31 no.3
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• pp.135-142
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• 2018

In this study, we have fabricated n-type $Bi_2Te_{2.85}Se_{0.15}$ compounds by different processing routes such as crushing, milling and mixing respectively. Subsequently, the obtained powders were consolidated by spark plasma sintering (SPS). The phase crystallinity of bulk samples were identified using X-ray diffraction technique. Powder morphology and fracture surface of bulk samples were observed using the scanning electron microscopy (SEM). The Seebeck coefficient and electrical conductivity values were significantly increased for the milling sample than crushing and mixing samples. As a result, the maximum power factor was obtained $2.4mW/mK^2$, which is thrice than that of crushing process. The maximum figure of merit (ZT) of 0.77 was achieved at 400 K for the milling sample. Furthermore, relatively high hardness and density values were noticed for the different processed samples.

• Journal of Powder Materials
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• v.18 no.5
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• pp.449-455
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• 2011

In this study, p-type $(AgSbTe_2)_{15}(GeTe)_{85}$: TAGS-85 compound powders were prepared by gas atomization process, and then their microstructures and mechanical properties were investigated. The fabricated powders were of spherical shape, had clean surface, and illustrated fine microstructure and homogeneous $AgSbTe_2$ + GeTe solid solution. Powder X-ray diffraction results revealed that the crystal structure of the TAGS-85 sample was single rhombohedral GeTe phase, which with a space group $R_{3m}$. The grain size of the powder particles increased while the micro Vickers hardness decreased with increasing annealing temperature within the range of 573 K and 723 K due to grain growth and loss of Te. In addition, the crystal structure of the powder went through a phase transformation from rhombohedral ($R_{3m}$) at low-temperature to cubic ($F_{m-3m}$) at high-temperature with increasing annealing temperature. The micro Vickers hardness of the as-atomized powder was around 165 Hv, while it decreased gradually to 130 Hv after annealing at 673K, which is still higher than most other fabrication processes.

• Korean Journal of Materials Research
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• v.10 no.3
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• pp.246-252
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• 2000

Thermoelectric properties of the $Bi_2(Te_{0.85}Se_{0.15})_3$ alloy, prepared by mechanical alloying and hot pressing, were investigated with the variation of the hot-pressing temperature ranging from $300^{\circ}C$ to $550^{\circ}C$. Contrary to the p-type behavior of single crystal, the hot-pressed $Bi_2(Te_{0.85}Se_{0.15})_3$ alloy exhibited n-type conduction without addition of donor dopant. When the $Bi_2(Te_{0.85}Se_{0.15})_3$ powders were annealed in $(50{\%}\;H_2+50{\%}\;Ar)$ atmosphere, the hot-pressed specimens exhibited a positive Seebeck coefficient due to the reduction of the electron concentration by removal of the oxide layer on the powder surface and annealing-out of the excess Te vacancies. Figure-of-merit of the hot-pressed $Bi_2(Te_{0.85}Se_{0.15})_3$ alloy was improved by hot pressing at temperatures above $450^{\circ}C$, and the maximum value of $1.92{\times}10^{-3}/K$ was obtained for the specimen hot-pressed at $550^{\circ}C$.

• Journal of the Microelectronics and Packaging Society
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• v.18 no.4
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• pp.55-61
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• 2011

The n-type $Bi_2(Te_{0.9}Se_{0.1})_3$ powers were fabricated by mechanical alloying, mixed with tungsten(W) powders, and hot-pressed at $550^{\circ}C$ for 30 minutes. Thermoelectric properties of the hot-pressed $Bi_2(Te_{0.9}Se_{0.1})_3$ were characterized as a function of the volume percent of tungsten-powder addition. The power factor of the hot-pressed $Bi_2(Te_{0.9}Se_{0.1})_3$ was $21.9{\times}10^{-4}$ $W/m-K^2$, and was improved to $30.5{\times}10^{-4}$ $W/m-K^2$ by dispersion of 1 vol% W powders. While the dimensionless figure-of-merit of the $Bi_2(Te_{0.9}Se_{0.1})_3$ hot-pressed without dispersion of W powders was measured as 0.52 at room temperature, it became substantially enhanced to 0.95 with addition of 1 vol% W powders.

• Korean Journal of Materials Research
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• v.10 no.4
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• pp.257-263
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• 2000

Thermoelectric properties of the 0.05wt% $SbI_3$-doped n-type $Bi_2(Te_{0.95}Se_{0.05})_3$ alloy, prepared by melting/grinding and hot pressing, were investigated with variation of the annealing time up to 36 hours. The electron concentration of the 0.05wt% SbI$_3$-doped n-type $Bi_2(Te_{0.95}Se_{0.05})_3$ alloy decreased with increasing the annealing time. The figure-of-merit of the 0.05wt% $SbI_3$-doped n-type $Bi_2(Te_{0.95}Se_{0.05})_3$ alloy was improved from $2.1{\times}10^{-3}/K$ to $2.35{\times}10^{-3}/K$ by annealing at $500^{\circ}C$ for 3 hours. When annealed longer than 12 hours, however, the figure-of-merit decreased substantially due to the increase of the electrical resistivity.