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Hamawandi et al. Energy Mater. 2025, 5, 500065 https://dx.doi.org/10.20517/energymater.2024.204 Page 3 of 20

[24]
challenging since it has low energy density . Binary and ternary metal chalcogenides perform well in this
temperature range, with bismuth telluride (Bi Te ) and antimony telluride (Sb Te ) (and their alloys) being
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the two most popular n- and p-type TE materials with high ZT, operation around room temperature,
[23]
effective up to 200 °C due to their specific band structure, high carrier mobility, and intrinsically low κ .
Bi Te and Sb Te are isostructural, with the structure along the c-axis composed of periodic quintuple layers
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[25]
(QL) with the sequence Te2-M-Te1-M-Te2, where M is Bi or Sb . Two tellurium atoms (Te1 and Te2) are
distinguished by their different local environments. Van der Waals (vdW) interactions between adjacent
Te2 layers hold the QL stacked together and influence the material's mechanical, electronic, and TE
properties.
TE materials have been synthesized through commonly used synthetic techniques, such as solid-state, gas-
phase, and wet chemical routes. Each method has its constraints and advantages, leading to materials with
different microstructures. Zone melting has long been the mainstream fabrication technique for the
fabrication of commercial bismuth-telluride-based solid solutions . Strategies for synthesizing
[26]
nanostructured Bi Te and Sb Te include mechanical alloying , physical vapor deposition , chemical
[28]
[27]
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[3]
[29]
reduction , hydrothermal , solvothermal , and thermolysis [17,31,32] routes. Different morphologies of
[30]
Bi Te and Sb Te (nanoparticles, nanowires, nanorods, and nanoplates) have been synthesized using these
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techniques. Over several decades, the ZT of these materials has improved. A detailed summary of
processing time, costs, scalability, and TE properties associated with different methods can be found in
earlier works [13,23,27] . However, a designed synthesis process is of great importance to produce the desired
compositions and structures effectively and overcome the challenges that have restricted the
commercialization of TE materials . Considering this, some of the techniques listed above might be
[12]
unsuitable for large-scale production due to their low purity, low yield, high energy cost, the possibility of
contamination, and considerable batch-to-batch variations leading to limited reproducibility [3,10] . High-
energy techniques such as zone melting, and melt alloying require typically high purity (5N) elemental
powders, glove boxes and vacuum lines for handling the powders, and high-temperature furnaces. Bi-Sb
tellurides grown by directional solidification, or zone-melting, method have poor mechanical properties
because the basal plane in this rhombohedral structure is also the cleavage plane . Among the wet-
[33]
chemical synthetic techniques, the thermolysis method efficiently produces highly crystalline
nanostructures with a narrow size distribution, high purity, and tunable morphology. Microwave (MW)
heating can serve as the energy source for these synthesis techniques. Due to the effective volume heating,
the MW-heating process is a fast, scalable, energy-efficient, and high-yield approach (with a high
reproducibility) to obtain materials with well-defined chemical composition, high phase purity, and
crystallinity. MW-assisted heating increases the overall kinetics of the reaction, hence resolving the problem
of prolonged reaction time (from several hours/days to a few minutes) of the method. There are only a few
reports [10,12,34-36] on the synthesis of Bi Te /Sb Te using the MW-assisted thermolysis method, where the
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transport properties of the produced materials are presented (see Supplementary Table 1). Moreover, the
number of studies examining detailed structural, microstructure analysis, surface morphology, and their
effects on transport properties of Bi Te and Sb Te compounds is also limited. This work aims to establish
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an alternative facile and sustainable wet-chemical synthesis route for the large-scale synthesis of
morphology-controlled, nanostructured n- and p-type TE materials (Bi Te and Sb Te ) through MW-
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assisted heating, with a focus on the time and energy efficiency, as well as the yield of the chemical process.
The process uses readily available precursors and does not require glove box or high-temperature furnaces.
We employed synchrotron radiation X-ray absorption spectroscopy (XAS) to gain insights into the local
atomic environment and lattice dynamics around Bi, Sb, and Te atoms using an advanced data analysis
technique such as reverse Monte Carlo (RMC) simulation. The as-made TE materials were consolidated
into pellets via spark plasma sintering (SPS) to evaluate the characteristics of the electrical and thermal
properties. Results indicate that the materials obtained exhibit a reasonable TE performance compared to