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Xie et al. Energy Mater. 2025, 5, 500127 https://dx.doi.org/10.20517/energymater.2025.48 Page 3 of 15
positively to thermoelectric performance by optimizing the carrier concentration and enhancing phonon
[13]
scattering .
In this study, Bi Sb Te was selected as the benchmark material for the development of high-performance
0.5
3-x
1.5
thermoelectric alloys. Our findings demonstrate that reducing tellurium content from x = 0 to x = 0.15
significantly enhances thermoelectric properties. This composition adjustment achieves a better balance
between carrier concentration and lattice thermal conductivity, retaining high electrical conductivity and a
relatively high Seebeck coefficient while promoting phonon scattering. As a result, a maximum ZT value of
approximately 1.15 at 360 K was obtained, indicating excellent energy conversion efficiency.

Due to the volatility of tellurium during the melt-spinning process, an annealing step was introduced prior
to rapid solidification. This thermal treatment stabilizes tellurium and prevents undesirable structural
degradation or decomposition during processing, thereby preserving the integrity of the final material. The
inclusion of annealing not only enhances phase stability but also improves the overall thermoelectric
performance and reliability of the resulting alloys.

Therefore, we adopted an integrated synthesis strategy comprising planetary ball milling, annealing, melt-
spinning, elemental compensation and SPS. Planetary ball milling facilitates uniform mixing and grain
refinement, thereby enhancing phonon scattering. Annealing stabilizes the tellurium content by minimizing
volatilization and suppressing structural transformations. Melt-spinning induces rapid solidification,
promoting uniform microstructure formation. Finally, SPS enables rapid densification with minimal grain
growth, preserving the nanoscale features essential for high thermoelectric efficiency [14,15] .

EXPERIMENTAL
Materials synthesis
Synthesis of Bi Sb Te 3-x
1.5
0.5
High-purity elemental powders of bismuth (Bi, 99.999%, 5N), antimony (Sb, 99.999%, 5N), and tellurium
(Te, 99.999%, 5N) were used as starting materials. The powders were weighed according to the nominal
composition of Bi Sb Te , with varying Te contents to investigate the effect of Te deficiency. The weighed
3-x
1.5
0.5
powders were loaded into a zirconia ball milling jar under an argon atmosphere and subjected to high-
energy mechanical alloying using a planetary ball mill. The milling was conducted at a rotational speed of
450 rpm for 10 h, with a ball-to-powder weight ratio of 20:1.

The mechanically alloyed powders were subsequently annealed at 627 K for 10 h in order to relieve internal
stress and promote phase formation. The annealed powders were then loaded into a quartz nozzle with an
inner diameter of 0.4 mm for the melt-spinning process. A rotating copper wheel with a surface speed of
approximately 39.3 m/s (3,000 rpm) was employed to rapidly solidify the molten alloys, forming
nanostructured ribbons of Bi Sb Te .
1.5
0.5
3-x
To compensate for potential elemental losses during melt spinning, energy-dispersive X-ray spectroscopy
(EDS) analyses were performed on the ribbons to assess and adjust the final composition toward the target
stoichiometry. The as-spun ribbons were pulverized into fine powders and consolidated using SPS (SPS-
515S, SYNTEX INC) at 753 K under an applied uniaxial pressure of 50 MPa for three minutes. The sintered
pellets had a diameter of 23 mm and a thickness of approximately 5 mm.

Materials characterizations
XRD (Rigaku MiniFlex) for SPSed pellets was performed on parallel and perpendicular planes of SPS
pressing direction. The microstructure was analyzed by scanning electron microscopy (SEM, JEOL JSM-