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Number of results: 4
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Abstract

One of the ways to decrease thermal conductivity is nano structurization. Cobalt triantimonide (CoSb3) samples with added indium or tellurium were prepared by the direct fusion technique from high purity elements. Ingots were pulverized and re-compacted to form electrodes. Then, the pulsed plasma in liquid (PPL) method was applied. All materials were consolidated using rapid spark plasma sintering (SPS). For the analysis, methods such as X-ray diffraction (XRD), scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) with a laser flash apparatus (LFA) were used. For density measurement, the Archimedes’ method was used. Electrical conductivity was measured using a standard four-wire method. The Seebeck coefficient was calculated to form measured Seebeck voltage in the sample placed in a temperature gradient. The preparation method allowed for obtaining CoSb3 nanomaterial with significantly lower thermal conductivity (10 Wm–1K–1 for pure CoSb3 and 3 Wm–1K–1 for the nanostructured sample in room temperature (RT)). The size of crystallites (from SEM observations) in the powders prepared was about 20 nm, joined into larger agglomerates. The Seebeck coefficient, α, was about –200 µVK–1 in the case of both dopants, In and Te, in microsized material and about –400 µVK–1 for the nanomaterial at RT. For pure CoSb3, α was about 150 µVK–1 and it stood at –50 µVK–1 for nanomaterial at RT. In bulk nanomaterial samples, due to a decrease in electrical conductivity and inversion of the Seebeck coefficient, there was no increase in ZT values and the ZT for the nanosized material was below 0.02 in the measured temperature range, while for microsized In-doped sample it reached maximum ZT = 0.7 in (600K).

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Authors and Affiliations

R. Zybała
M. Schmidt
K. Kaszyca
M. Chmielewski
M.J. Kruszewski
M. Jasiński
M. Rajska
Ł. Ciupiński
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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

Doping is one of the possible ways to significantly increase the thermoelectric properties of many different materials. It has been confirmed that by introducing bismuth atoms into Mg sites in the Mg2Si compound, it is possible to increase career concentration and intensify the effect of phonon scattering, which results in remarkable enhancement in the figure of merit (ZT) value. Magnesium silicide has gained scientists’ attention due to its nontoxicity, low density, and inexpensiveness. This paper reports on our latest attempt to employ ultrafast selfpropagating high-temperature synthesis (SHS) followed by the spark plasma sintering (SPS) as a synthesis process of doped Mg2Si. Materials with varied bismuth doping were fabricated and then thoroughly analyzed with the laser flash method (LFA), X-ray diffraction (XRD), scanning electron microscopy (SEM) with an integrated energy-dispersive spectrometer (EDS). For density measurement, the Archimedes method was used. The electrical conductivity was measured using a standard four-probe method. The Seebeck coefficient was calculated from measured Seebeck voltage in the sample subjected to a temperature gradient. The structural analyses showed the Mg2Si phase as dominant and Bi2Mg3 located at grain boundaries. Bismuth doping enhanced ZT for every dopant concentration. ZT = 0:44 and ZT=0.38 were obtained for 3wt% and 2wt% at 770 K, respectively.
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Authors and Affiliations

Bartosz Bucholc
1
ORCID: ORCID
Kamil Kaszyca
1
ORCID: ORCID
Piotr Śpiewak
2
ORCID: ORCID
Krzysztof Mars
3
ORCID: ORCID
Mirosław J. Kruszewski
2
ORCID: ORCID
Łukasz Ciupiński
2
ORCID: ORCID
Krystian Kowiorski
1
ORCID: ORCID
Rafał Zybała
1 2
ORCID: ORCID

  1. Łukasiewicz Research Network - Institute of Microelectronics and Photonics, Aleja Lotników 32/46, 02-668 Warsaw, Poland
  2. Faculty of Materials Science and Engineering, Warsaw University of Technology, Wołoska 141, 02-507 Warsaw, Poland
  3. Faculty of Materials Science and Ceramic, AGH University of Science and Technology, Kraków, Al. Mickiewicza 30, 30-059, Poland
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Abstract

Due to air pollution, global warming and energy shortage demands new clean energy conversion technologies. The conversion of industrial waste heat into useful electricity using thermoelectric (TE) technology is a promising method in recent decades. Still, its applications are limited by the low efficiency of TE materials in the operating range between 400-600 K. In this work, we have fabricated Cu0.005Bi0.5Sb1.495Te3 powder using a single step gas atomization process followed by spark plasma sintering at different temperatures (623, 673, 723, and 773 K), and their thermoelectric properties were investigated. The variation of sintering temperature showed a significant impact on the grain size. The Seebeck coefficient values at room temperature increased significantly from 127 μVK to 151 μV/K with increasing sintering temperature from 623 K to 723 K due to decreased carrier concentration. The maximum ZT values for the four samples were similar in the range between 1.15 to 1.18 at 450 K, which suggest these materials could be used for power generation in the mid-temperature range (400-600 K).

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Authors and Affiliations

Chul-Hee Lee
Peyala Dharmaiah
Jun-Woo Song
Kwang-Yong Jeong
Soon-Jik Hong

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