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Page 4 of 15 Xie et al. Energy Mater. 2025, 5, 500127 https://dx.doi.org/10.20517/energymater.2025.48

5310) in low vacuum mode for enhanced imaging quality and detail. The temperature dependence of
electrical conductivity and Seebeck coefficients was measured from 300 to 482 K using a commercially
available instrument (ZEM-3, ULVAC-RIKO, Japan) apparatus, ensuring precise thermal and transport
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property analysis. The specimen size is typically parallel piped with the dimensions of 5 × 5 × 15 mm . The
thermal conductivity values of the pellet specimen with a dimension of 2 mm in thickness and 23 mm in
diameter measured from 300 to 482 K were measured by hot disk (TPS 3500). Based on the above data, we
can obtain the ZT value through calculation. Figure 1 shows the schematic diagram of experimental process.
First, we begin with planetary ball milling synthesis, followed by annealing and melt spinning. Since element
loss can occur during the melt spinning process, we perform EDS measurements after melt spinning to
determine the elemental composition and compensate to achieve the desired stoichiometry. Finally, we
proceed with SPS.

RESULTS AND DISCUSSION
The XRD patterns presented in Figure 2 provide comprehensive insights into the structural evolution of
Bi Sb Te under various synthesis and processing conditions. Figure 2A compares samples subjected to
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three different treatments: 3-h ball milling (3h-BM), 10-h ball milling (10h-BM), and 10-h ball milling
followed by 10-h annealing (10h-BM + AN). The 3h-BM sample displays broad and less intense diffraction
peaks, indicative of poor crystallinity. This can be attributed to inadequate mechanical activation and
smaller grain sizes due to the shorter milling duration. In contrast, the 10h-BM sample exhibits significantly
sharper and more intense peaks, suggesting enhanced crystallinity facilitated by extended milling, which
promotes more uniform grain formation and better particle refinement. Subsequent annealing of the 10h-
BM sample (10h-BM + AN) further sharpens the diffraction peaks and improves their alignment with the
[16]
standard reference pattern (JCPDS 00-49-1713) , confirming improved phase purity and crystallite growth.
This observation highlights the synergistic effect of prolonged mechanical alloying and thermal treatment in
enhancing the structural quality of Bi Sb Te . Considering the temperature-sensitive nature of tellurium
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and its propensity for phase transitions, improper thermal control can lead to the formation of undesirable
phases during melt spinning. The annealing step thus plays a critical role in stabilizing the crystalline
structure before subsequent processing, mitigating abrupt phase changes and promoting controlled
structural evolution.

Figure 2B further elucidates the influence of melt spinning and tellurium (Te) content variation on the
structural characteristics of Bi Sb Te . Four processing routes are examined BST-BM + AN + SPS, BST-
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BM + AN + MS + SPS, BST-BM + AN + MS + SPS (with 15 wt% additional Te), and BST-BM + AN + MS +
SPS (with 25 wt% additional Te). The BST-BM + AN + SPS sample shows well-resolved diffraction peaks
corresponding to the Bi Sb Te phase, indicating successful crystallization. The introduction of a melt
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spinning step (BST-BM + AN + MS + SPS) further enhances the peak intensity and sharpness, reflecting
improved crystallinity and finer grain refinement. The addition of Te during processing, especially at
25 wt%, results in even more pronounced diffraction peaks. This suggests that excess Te plays a role in
stabilizing the Bi Sb Te phase and suppressing the formation of structural defects or secondary
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phases [17,18] . These results emphasize the critical importance of both processing technique and compositional
tuning in optimizing the microstructural properties of thermoelectric materials [19,20] .
Prolonged ball milling, annealing and melt spinning collectively contribute to the enhancement of
crystallinity in Bi Sb Te , as evidenced by the emergence of sharper and more intense XRD peaks. Notably,
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samples subjected to melt spinning exhibit significantly more pronounced diffraction peaks compared to
those processed without this step, indicating a substantial improvement in crystal structure refinement. In
contrast, samples prepared with shorter processing durations or without post-treatment display broader and