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Page 6 of 15 Xie et al. Energy Mater. 2025, 5, 500127 https://dx.doi.org/10.20517/energymater.2025.48

less intense peaks, suggesting reduced crystallinity and the presence of smaller grain sizes. These
observations underscore the critical importance of synthesis strategies and compositional control in
optimizing the crystalline structure of Bi Sb Te . The combined effects of extended ball milling, thermal
1.5
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0.5
annealing, melt spinning and appropriate elemental compensation play a pivotal role in improving the
structural integrity of the material, thereby laying the foundation for enhanced thermoelectric performance.
Traditionally, thermoelectric materials have been synthesized through ball milling followed by SPS. In
contrast, the present study employs a modified approach involving ball milling followed by melt spinning.
This method allows for more precise control over the material's microstructure and results in improved
uniformity compared to conventional ball milling alone. Ball milling and melt spinning are fundamentally
different techniques, each yielding distinct microstructural features due to their inherent processing
mechanisms.

As illustrated in Figure 3A and B, ball milling is a high-energy mechanical process that subjects material
particles to repeated fracturing, cold welding and re-fracturing. It is widely utilized for particle refinement,
homogenization and alloying purposes [21,22] . Typically, ball milling yields nanocrystalline grains in the range
of 10 to 100 nm, attributed to severe plastic deformation and dynamic recrystallization . The process also
[23]
introduces a high density of lattice defects, such as dislocations, grain boundaries and vacancies, which can
significantly enhance atomic diffusion and facilitate phase transformations. With extended milling
durations, ball milling can promote atomic-scale homogenization, resulting in solid solutions or finely
dispersed composite structures. In certain cases, it may even induce amorphization by disrupting long-
range atomic order . The resultant particles generally exhibit irregular morphologies and broad particle
[24]
size distributions. The specific microstructural characteristics are largely dependent on parameters such as
milling duration, impact energy and the intrinsic properties of the starting materials.

Figure 3C and D depicts the annealing treatment employed prior to melt spinning, which is essential to
minimize tellurium (Te) volatilization during subsequent processing. Figure 3E and F highlights the
microstructural features produced by melt spinning, a rapid solidification technique that offers several
advantages over ball milling. One of the primary benefits is the extremely high cooling rates on the order of
10 to 10 K/s which enable the formation of amorphous or metastable phases that are difficult to achieve
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through mechanical milling . This rapid quenching process promotes superior compositional uniformity
[25]
by suppressing phase segregation and facilitating the retention of homogenous microstructures [26,27] .
Compared to the time-intensive and mechanically demanding ball milling process, melt spinning is both
faster and more energy-efficient. Additionally, it reduces the risk of contamination and excessive defect
formation, which are often associated with repeated mechanical collisions in ball milling.

Furthermore, melt spinning is particularly effective for producing thin ribbons or films with smooth,
continuous surfaces, in contrast to the irregularly shaped particles typically obtained from ball milling.
These attributes make melt spinning a favorable technique for fabricating advanced functional materials,
especially in applications that require controlled microstructures, such as magnetic alloys, amorphous
metals and high-performance thermoelectric or coating materials .
[28]

Figure 4A shows a SEM image revealing the microstructure of the sample. A specific region of interest,
marked by a pink box, indicates the area selected for further elemental analysis. A yellow cross within the
region denotes the precise location where Energy-Dispersive X-ray Spectroscopy (EDS) was performed.
Figure 4B displays the elemental mapping of tellurium (Te), represented in green. The mapping reveals a
relatively uniform distribution of Te throughout the analyzed region, suggesting that Te is a well-