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Page 2 of 20 Hamawandi et al. Energy Mater. 2025, 5, 500065 https://dx.doi.org/10.20517/energymater.2024.204

(523 K) for n-type Bi Te and p-type Sb Te , respectively, shifted significantly to the high-temperature region when
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compared to earlier reports, highlighting their potential for power generation applications. The scalable, energy-
and time-efficient synthetic method developed, along with the demonstration of its potential for TE materials,
opens the door for a wider application of these materials with minimal environmental impact.
Keywords: Thermoelectric materials, microwave-assisted synthesis, X-ray absorption spectroscopy, reverse
Monte Carlo simulations, TE figure-of-merit, thermolysis

INTRODUCTION
The fast-changing and ever-increasing global energy demand has resulted in various fossil fuel-related
environmental challenges, necessitating the development of renewable, affordable, and efficient energy
supplies and energy-harvesting strategies . Thermoelectric (TE) materials and devices can directly
[1-3]
interconvert between heat and electrical power, which could contribute to energy generation, utilization,
and environmental impact . Based on the two fundamental phenomena, Seebeck and Peltier effects, TE
[3,4]
[1,5]
devices may function as TE generators (TEGs) for harvesting heat energy or as coolers (TECs) . TE
materials-based technologies can be employed in various applications, including medical and wearable
devices, low-power devices such as the Internet of Things (IoT), on-chip cooling, self-powering gadgets,
solar cells, battery-free sensors, and space missions [1,5,6] . Thermal energy can be harvested from different
low-grade heat sources, such as cars, buildings, electronic equipment, and the human body.

Unlike conventional electricity-generating technologies, TE devices function without the contribution of
mechanical energy, making them reliable. They can operate under wide working temperature ranges
without vibrations and noise, are easy to maintain, and have extended operational lifetime, among their
[6-8]
attractive features . However, low conversion efficiency, manufacturing challenges, complexity, and
materials costs of this technology hinder its broad application [9,10] . The dimensionless TE figure of merit
(ZT), expressed as ZT = S σT/κ, describes the efficiency of a TE material, where σ is the electrical
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conductivity, S is the Seebeck coefficient, T is the absolute temperature, and κ is the thermal
conductivity [10-12] . The formula suggests that an ideal TE is a “phonon glass electron crystal”, allowing charge
carriers to flow freely (high σ) while maintaining a temperature difference across the material (low thermal
conductivity) [10,13] . In addition, the material's band structure is critical for maintaining the thermal voltage
(high S) [9,13] . Therefore, semiconductor materials, in general, are favorable as TE materials. However, since
S, σ, and κ have an inherent correlation in classical materials, improving the ZT has been challenging [14-16] .
One of the crucial strategies to enhance the ZT is based on increasing phonon scattering through
nanostructuring , producing nanoprecipitates , porosity design , alloying, and grain boundary
[17]
[18]
[19]
engineering [20,21] . So far, numerous research efforts based on theoretical predictions and experimental
explorations have shown that nanostructuring could considerably improve the performance of TE materials
by lowering the negative correlation of TE transport characteristics. Due to a large density of interfaces
(point defects/grain boundaries) in nanostructures, phonons are scattered more efficiently than electrons,
since the mean free paths of heat carriers are longer than those of charge carriers. This results in a reduction
in κ (based on the phonon-blocking effect) while not considerably affecting the mobility of charge
carriers [22,23] . Moreover, based on the quantum confinement phenomena, nanostructuring may widen the
band gap and discretization in the electronic density of states, enhancing the S [13,17] .

TE materials are categorized into three groups based on their operational temperature range: ambient, mid-
and high-temperature. The band gap and chemical stability of these materials determine the feasibility of a
given composition as a TE material. Most of the generated waste heat is attributed to temperatures below
200 °C, referred to as low-temperature waste heat. However, capturing and reusing low-grade waste heat is