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Reduction of Thermal Conductivity Through Complex Microstructure by Dispersion of Carbon Nanofiber in p-Type Bi0.5Sb1.5Te3 Alloys

Sharief P., Madavali B., Sohn Y., Han J. H., Song G., Hong S. J.

Archives of Metallurgy and Materials

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2021

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Vol. 66, iss. 3

803--808

EN

The influence of nano dispersion on the thermoelectric properties of Bi2Te3 was actively investigating to wide-spread thermoelectric applications. Herein this report, we have systematically controlled the microstructure of Bi0.5Sb1.5Te3 (BST) alloys through the incorporation of carbon nanofiber (CNF), and studied their effect on thermoelectric properties, and mechanical properties. The BST/x-CNF (x-0, 0.05, 0.1, 0.2 wt.%) composites powder was fabricated using high energy ball milling, and subsequently consolidated the powder using spark plasma sintering. The identification of CNF in bulk composites was analyzed in Raman spectroscopy and corresponding CNF peaks were recognized. The BST matrix grain size was greatly reduced with CNF dispersion and consistently decreased along CNF percentage. The electrical conductivity was reduced and Seebeck coefficient varied in small-scale by embedding CNF. The thermal conductivity was progressively diminished, obtained lattice thermal conductivity was lowest compared to bare sample due to induced phonon scattering at interfaces of secondary phases as well as highly dense fine grain boundaries. The peak ZT of 0.95 achieved for 0.1 wt.% dispersed BST/CNF composites. The Vickers hardness value of 101.8 Hv was obtained for the BST/CNF composites.

2

Effects of Milling Duration on the Thermoelectric Properties of n-Type Bi2Te2.7Se0.3

Park Min-Soo, Koo Hye-Young, Park Yonh-Ho, Ha Gook-Hyun

Archives of Metallurgy and Materials

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2019

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Vol. 64, iss. 2

591--595

EN

In this study, an oxide reduction process and a reduction-sintering process were employed to synthesize a thermoelectric alloy from three thermoelectric composite oxide powders, and the thermoelectric properties were investigated as a function of the milling duration. Fine grain sizes were analyzed by via X-ray diffraction and scanning electron microscopy, to investigate the influence of the milling duration on the synthesized samples. It was found that microstructural changes, the Seebeck coefficient, and the electrical resistivity of the compounds were highly dependent on the sample milling duration. Additionally, the carrier concentration considerably increased in the samples milled for 6 h; this was attributed to the formation of antisite defects introduced by the accumulated thermal energy. Moreover, the highest value of ZT (=1.05) was achieved at 373K by the 6-h milled samples. The temperature at which the ZT value maximized varied according to the milling duration, which implies that the milling duration of the three thermoelectric composite oxide powders should be carefully optimized for their effective application.

3

Effect of Pd-P Layer on the Bonding Strength of Bi-Te Thermoelectric Elements

Bae Sung Hwa, Han Se Hun, Son Injoon, Kim Kyung Tae

Archives of Metallurgy and Materials

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2019

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Vol. 64, iss. 3

963--968

EN

In this study, the effect of electroless Pd-P plating on the bonding strength of the Bi-Te thermoelectric elements was investigated. The bonding strength was approximately doubled by electroless Pd-P plating. Brittle Sn-Te intermetallic compounds were formed on the bonding interface of the thermoelectric elements without electroless Pd-P plating, and the fracture of the bond originated from these intermetallic compounds. A Pd-Sn solder reaction layer with a thickness of approximately 20 μm was formed under the Pd-P plating layer in the case of the electroless Pd-P plating, and prevented the diffusion of Bi and Te. In addition, the fracture did not occur on the bonding interface but in the thermoelectric elements for the electroless Pd-P plating because the bonding strength of the Pd-Sn reaction layer was higher than the shear strength of the thermoelectric elements.

4

Effect of Surfactant Addition on Bi2Te3 Nanostructures Synthesized by Hydrothermal Method

Dharmaiah P., Lee C. H., Madavali B., Hong S.-J.

Archives of Metallurgy and Materials

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2017

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Vol. 62, iss. 2B

1005--1010

EN

In the present work, we have prepared Bi2Te3 nanostructures with different morphologies such as nano-spherical, nanoplates and nanoflakes obtained using various surfactant additions (EG, PVP, and EDTA) by a hydrothermal method. The shape of the nanoparticles can be controlled by addition of surfactants. The samples were characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM). It is found that the minority BiOCl phase disappears after maintained pH at 10 with EG as surfactant. SEM bulk microstructure reveals that the sample consists of fine and coarse grains. Temperature dependence of thermoelectric properties of the nanostructured bulk sample was investigated in the range of 300-450K. The presence of nanograins in the bulk sample exhibits a reduction of thermal conductivity and less effect on electrical conductivity. As a result, a figure of merit of the sintered bulk sample reached 0.2 at 400 K. A maximum micro Vickers hardness of 102 Hv was obtained for the nanostructured sample, which was higher than the other reported results.

5

SEM studies of ore minerals in skarns from Garby Izerskie, Karkonosze-Izera block, south-western Poland

Rybicki M., Karwowski Ł., Banasik K.

Contemporary Trends in Geoscience

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2013

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Vol. 2, iss. 1

61--66

EN

In “Stanisław” quarry, that is located on Garby Izerskie, ore minerals-bearing calcsilicate skarns were found in 2009. The samples were studied using microscopical method of reflected light and scanning electron microscopy (SEM). Based on SEM study, the predominant ore minerals in investigated samples are chalcopyrite, pyrrhotite, bismuth telluride and native bismuth. Moreover, acanthite, native gold and native silver were also identified. Our studies are the first report of above mentioned minerals from the Garby Izerskie area.

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Preliminary data on bismuth telluride from Izerskie Garby zone, Karkonosze-Izera Block, South-Western Poland

Rybicki M.

Contemporary Trends in Geoscience

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2012

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Vol. 1, iss. 1

63--65

EN

This paper describes the first occurrence of bismuth telluride in the Izerskie Garby contact zone. In nature, there are 4 known bismuth tellurides: hedleyite (Bi7Te3), pilsenite (Bi4Te3), tsumoite (BiTe) and tellurobismuthite (Bi2Te3). They are typical accessory minerals of the polymetallic skarns. The Ca-skarns of the "Stanisław" quarry in the Izerskie Garby, bismuth telluride occurs in association with pyrrhotite, chalcopyrite, sphalerite, and wollastonite and tend to form irregular clusters up to 40μm long and 15μm width . Research methods used so far (SEM) does not allow for unequivocal identification of studied mineral. Therefore, it is necessary to conduct further tests using the electron microprobe.

PL

Niniejsza praca opisuje pierwsze wystąpienie tellurku bizmutu w strefie kontaktowej Izerskich Garbów. W przyrodzie znane są 4 tellurki bizmutu: hedleyit (Bi7Te3), pilsenit (Bi4Te3), tsumoit (BiTe) oraz tellurobizmutyt (Bi2Te3). Są to typowe minerały akcesoryczne występujące głównie w polimetalicznych skarnach. W Ca-skarnach z kopalni “Stanisław” w Izerskich Garbach, tellurek bizmutu występuje w asocjacji z pirotynem, chalkopirytem, sfalerytem oraz wollastonitem i tworzy nieregularne skupienia o długości do 40 µm i szerokości 15 µm. Wykorzystane do tej pory metody badawcze (SEM) nie pozwalają na jedno-znaczną identyfikację tego minerału. W związku z tym konieczne jest przeprowadzenie dalszych badań z wykorzystaniem mikrosondy elektronowej.