Abstract
In order to realize high-performance thermoelectric materials, a way to obtain small grain size is necessary for intensification of the phonon scattering. Here, we use a melt-spinning-spark plasma sintering process for making p-type Bi0.36Sb1.64Te3 thermoelectric materials and evaluate the relation between the process conditions and thermoelectric performance. We vary the Cu wheel rotation speed from 1000 rpm (~13 ms−1) to 4000 rpm (~52 ms−1) during the melt spinning process to change the cooling rate, allowing us to control the characteristic size of nanostructure in melt-spun Bi0.36Sb1.64Te3 ribbons. The higher wheel rotation speed decreases the size of nanostructure, but the grain sizes of sintered pellets are inversely proportional to the nanostructure size after the same sintering condition. As a result, the ZT values of the bulks fabricated from 1000–3000 rpm melt-spun ribbons are comparable each other, while the ZT value of the bulk from the 4000 rpm melt-spun ribbons is rather lower due to reduction of grain boundary phonon scattering. In this work, we can conclude that the smaller nanostructure in the melt spinning process does not always guarantee high-performance thermoelectric bulks, and an adequate following sintering process must be included.
Highlights
The increasing world-wide demands on new technology for CO2 reduction and global warming have induced the development of highly-efficient energy harvesting technology that reuses exhausted energy and shifts from fossil fuels to renewable energy and replaces it with new energy sources.Currently, more than 60% of primary energy used in industry or in combustion engines is lost as waste heat
More than 60% of primary energy used in industry or in combustion engines is lost as waste heat
The efficiency of thermoelectric (TE) devices is highly related with the performance of TE materials, which is determined by a dimensionless figure of merit, ZT, calculated by ZT = σS2 T/κ, where σ, S, T, and κ are the electrical conductivity, Seebeck coefficient, absolute temperature, and thermal conductivity, respectively [3,4]
Summary
The increasing world-wide demands on new technology for CO2 reduction and global warming have induced the development of highly-efficient energy harvesting technology that reuses exhausted energy and shifts from fossil fuels to renewable energy and replaces it with new energy sources. Thermoelectricity is considered to be one of the encouraging energy harvesting technologies in the view of changing waste heat into electricity in the semiconductor materials [1,2]. L is the Lorenz number [9] In this context, many researchers are focusing on the κlat reduction which is considered as an independent variable to enhance TE performance [1,8,10,11]. The continuous attempts to reduce grain size of the TE materials have been tried via high-energy ball milling [15,16], spark erosion [17], melt spinning (MS) [8,18,19,20], and bottom-up chemical synthesis processes [21,22,23]. It is necessary to investigate the process variables, leading to different microstructures and transport properties which are critical factors for TE performance. We have investigated the change of microstructure and TE properties of polycrystalline bulks of Bi0.36 Sb1.64 Te3 fabricated by combined technique of MS and spark plasma sintering (SPS) in an effort to optimize the process parameters for nanograin structured TE materials
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