Abstract
In this study, Bi0.5Sb1.5Te3.0 (BST) nanoparticles (NPs) with high crystallinities were synthesized via a mechanochemical process (MCP). X-ray diffraction (XRD), and Raman and X-ray photoelectron spectroscopy (XPS) spectra of the BST NPs showed that the Bi, Sb, and Te powders successfully formed BiSbTe phase and transmission electron microscopy (TEM) images, verifying the high crystallinity and smaller size, albeit agglomerated. The as-synthesized BST NPs with agglomerated clusters were ground into smaller sizes of approximately 41.8 nm with uniform distribution through a simple wet-milling process during 7 days. The thermal conduction behaviors of bulk alloys fabricated by spark plasma sintering (SPS) of the BST NPs were studied by comparing those of samples fabricated from as-synthesized BST NPs and a BST ingot. The thermal conductivities (κ) of the BST nanocomposites were significantly reduced by introducing BST NPs with smaller grain sizes and finer distributions in the temperature range from 300 to 500 K. The BST nanocomposites fabricated from wet-milled BST NPs offered ultralow κ values of 0.84 W m−1 K−1 at approximately 398 K.
Highlights
Over the past few decades, thermoelectric (TE) materials, which can directly convert heat into electricity based on the Seebeck effect, have received significant attention because they possess the ability to harvest waste heat, and can serve as useful energy resources [1,2,3]
The crystallinity and phase purity of as-synthesized BST NPs were determined via X-ray diffraction (XRD, P1, Bruker, Billerica, MA, USA) at a scan rate of 0.5 ◦/s with Cu Kα radiation (λ = 1.54 Å) and Raman spectroscopy (LabRAM ARAMIS, Horiba, Kyoto, Japan) with an Ar-ion laser (λ = 514.5 nm) as the excitation source, where the Raman scattered light signal was collected in a backscattering geometry using the × 50 microscope objective lens
After 30 min, the peaks of pure elements disappeared, and the characteristic peak of BST was suddenly revealed because the mechanochemical process (MCP) accompanied an abrupt phase change during the formation of the compound [27]
Summary
Over the past few decades, thermoelectric (TE) materials, which can directly convert heat into electricity based on the Seebeck effect, have received significant attention because they possess the ability to harvest waste heat, and can serve as useful energy resources [1,2,3]. Among a variety of routes for introducing nanostructures into bulk TE materials, the mechanochemical process (MCP) is an effective approach to obtain alloy NPs from elemental precursors by self-ignition and propagation reaction during high-energy ball milling under dry conditions [18,19,20,21,22,23]. This method is advantageous for designing TE materials because of the facile fabrication process that facilitates large-scale TE NP production, wherein the NPs serve to provide smaller grain sizes and larger grain boundaries for lower κl values. The mild wet-milling process was performed for 7 days in a Nalgene bottle (150 mL) containing BST powder (4 g), anhydrous ethanol, and ZrO2 balls with a diameter of 1 mm, followed by drying in a vacuum oven to obtain powder
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