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Abstract

The sintering behavior of p-type bismuth telluride powder is investigated by means of dilatometric analysis. The alloy powders, prepared by ball milling of melt-spun ribbons, exhibit refined and flake shape. Differential thermal analysis reveals that the endothermic peak at about 280oC corresponds to the melting of bismuth, and peaks existing between 410oC and 510oC are presumably due to the oxidation and crystallization of the powder. The shrinkage behavior of ball-milled powders was strongly dependent of heating rate by the thermal effect exerted on specimens. In the case of 2oC/min, the peak temperature for the densification is measured at 406oC, while the peak temperature at a heating rate of 20oC/min is approximately 443oC. The relative density of specimen pressureless-sintered at 500oC exhibited relatively low value, and thus further study is required in order to increase the density of sintered body.

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Authors and Affiliations

Ju-Yeon Han
Jongmin Byun
ORCID: ORCID
Young-In Lee
ORCID: ORCID
Byung Joon Choi
ORCID: ORCID
Hogyoung Kim
Sung-Tag Oh
ORCID: ORCID
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Abstract

The resistivity, Seebeck coefficient and thermal diffusivity were determined for Bi2Te3 + Ag2Te composite mixtures. Subsequent measurements were carried out in the temperature range from 20 to 270°C, and for compositions from pure Bi2Te3 to xAg2Te = 0.65 selected along the pseudo-binary section of Ag-Bi-Te ternary system. It was found that conductivity vs. temperature dependence shows visible jump between 140 and 150°C in samples with highest Ag2Te content, which is due to monoclinic => cubic Ag2Te phase transformation. Measured Seebeck coefficient is negative for all samples indicating they are n-type semiconductors. Evaluated power factor is of the order 1.52·10–3 and it decreases with increasing Ag2Te content (at. %). Recalculated thermal conductivity is of the order of unity in W/(m K), and is decreasing with Ag2Te addition. Finally, evaluated Figure of Merit is 0.43 at 100°C and decreases with temperature rise.
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Authors and Affiliations

S. Drzewowska
1
ORCID: ORCID
Tian-Wey Lan
2
ORCID: ORCID
B. Onderka
1
ORCID: ORCID

  1. AGH University of Science and Technology in Krakow, Faculty of Non-Ferrous Metals, 30 Mickiewicza Avenue, 30-059 Krakow, Poland
  2. Institute of Physics, Academia Sinica, Taipei 11529, Taiwan, ROC
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Abstract

The Sn-Ag-Cu-based solder paste screen-printing method has primarily been used to fabricate Bi2Te3-based thermoelectric (TE) modules, as Sn-based solder alloys have a low melting temperature (approximately 220℃) and good wettability with Cu electrodes. However, this process may result in uneven solder thickness when the printing pressure is not constant. Therefore, we suggested a novel direct-bonding method between the Bi2Te3-based TE elements and the Cu electrode by electroplating a 100 µm Sn/ 1.3 µm Pd/ 3.5 µm Ni bonding layer onto the Bi2Te3-based TE elements. It was determined that there is a problem with the amount of precipitation and composition depending on the pH change, and that the results may vary depending on the composition of Pd. Thus, double plating layers were formed, Ni/Pd, which were widely commercialized. The Sn/Pd/Ni electroplating was highly reliable, resulting in a bonding strength of 8 MPa between the thermoelectric and Cu electrode components, while the Pd and Ni electroplated layer acted as a diffusion barrier between the Sn layer and the Bi2Te3 TE. This process of electroplating Sn/Pd/Ni onto the Bi2Te3 TE elements presents a novel method for the fabrication of TE modules without using the conventional Sn-alloy-paste screen-printing method.
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Bibliography

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Authors and Affiliations

Seok Jun Kang
1
ORCID: ORCID
Sung Hwa Bae
2
ORCID: ORCID
Injoon Son
1
ORCID: ORCID

  1. Kyungpook National University, Department of Materials Science and Metallurgical Engineering, Daegu, Republic of Korea
  2. Kyushu University, Graduate School of Engineering, Department of Materials Process Engineering, Fukuoka, Japan

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