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Hamawandi et al. Energy Mater. 2025, 5, 500065 https://dx.doi.org/10.20517/energymater.2024.204 Page 15 of 20

The κ values were determined by measuring the thermal diffusivity, mass density, and heat capacity of
tot
samples. Figure 9D illustrates the κ of SPS-consolidated samples. The microstructure analysis of the
tot
sintered samples [Figure 4] reveals smaller grains and, consequently, a higher density of grain boundaries in
Bi Te , resulting in a lower κ . The overall upward trend in κ for both the samples is attributed to the
3
2
tot
tot
bipolar effect in materials with a narrow band gap, and minority charge carriers are easily excited as the
temperature increases, contributing to enhanced heat conduction and introducing increased κ to the
tot
samples [64,65] . Across the entire temperature range, it is evident that the κ for both samples remains
tot
consistently below 0.96 W/m·K. This observation underscores the significant impact of nanostructuring,
anisotropy, and texturing on the phonon scattering mechanism. In an earlier work on wet-chemically
synthesized Bi Sb Te , room temperature κ values in the range 1-1.9 W/m·K have been reported for
x
3
2-x
tot
materials with similar composition . Furthermore, studies performed on various nanostructures of Bi Te /
[60]
3
2
[66]
Sb Te revealed room temperature κ values of 1.47 and 1.81 W/m·K . Our κ values are about 10% to 50%
2
tot
3
tot
lower than these values, which may be associated with the increase in anisotropy due to the large layered
microstructure of the samples.
The ZT has been calculated for both samples based on their electrical and thermal transport data, and the
results are presented in Figure 9E. At room temperature, the ZT value for the Sb Te sample is 0.65, reaching
2
3
its highest value of 0.9 at 523 K. The ZT for Bi Te exhibits a linear increase with increasing temperature,
3
2
starting from about 0.35 at room temperature, reaching its peak value of 0.7 at 573 K. A comparison of ZT
values for Bi Te and Sb Te samples in this work with the earlier reports is presented in Figure 10. Bi Te
2
3
3
3
2
2
[67]
synthesized through thermolysis showed a ZT of 0.62 (at 400 K) . A ZT value of 0.84 (at 423 K) was
reported for Bi Te synthesized through the reduction of mechanically milled oxide powders , and 0.36 (at
[68]
2
3
[60]
325 K) for the solvothermally synthesized sample . We have earlier reported ZT values of 0.9 (at 373 K)
and 1.03 (at 473 K) for single-phase sintered Bi Te synthesized using MW-assisted polyol and hydrothermal
2
3
[3]
techniques . Furthermore, we reported earlier a ZT value of 1.37 (at 523 K) for single-phase sintered Sb Te
2
3
samples synthesized via the MW-assisted polyol route . An earlier work on Sb Te prepared using MW-
[49]
2
3
[70]
assisted thermolysis (~15 min) showed a ZT of 0.96 (at 423 K) . A ZT of 0.55 was reported for
[69]
hydrothermally synthesized Sb Te . Meanwhile, MW-assisted polyol synthesis yielded a ZT of 0.58 (at
2
3
[36]
420 K) . At last, Sb Te synthesized through solvothermal method yielded a ZT of 0.13 (at 423 K) As can
[71]
2
3
be seen from these values, the highest ZT achieved for these materials (and the temperature at which the
reported ZT is reached) is rather scattered for the TE materials with the same composition, which can be
attributed to the different synthetic methods employed, which substantially influence the resulting
microstructure, surface chemistry, and the type and content of impurity phases. These variables significantly
influence the overall TE performance of the materials. One important advantage of the presented synthesis
route is the easy dispersibility of the as-synthesized materials in polymer matrices, enabling very
[32]
homogeneous hybrid material design . With substantially reduced time and carbon footprint, the
developed synthetic method provides a promising sustainable approach for large-scale synthesis of high-
purity nanostructured TE materials with promising performance, at a yield greater than 95%. It is important
to note that the maximum ZT temperature of samples presented here shifted significantly to the high-
temperature region, highlighting their potential for power generation applications.
CONCLUSIONS
A rapid, energy-efficient, and scalable solution-based synthesis method was developed, using MW-assisted
thermolysis process - at 220 °C within 6 min, obtaining successfully bismuth and antimony telluride (Bi Te ,
3
2
Sb Te ) as n- and p-type TE materials. As-made materials were characterized using various techniques,
2
3
comprising XRPD, SEM, TEM, XAS, and XPS. XRPD confirmed a rhombohedral layered crystal structure,
while SEM revealed hexagonal platelet-shaped nanoparticles with lateral dimensions in the range of