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Page 4 of 20 Hamawandi et al. Energy Mater. 2025, 5, 500065 https://dx.doi.org/10.20517/energymater.2024.204

many earlier reports, utilizing wet-chemical synthetic routes.

EXPERIMENTAL
Materials
Bismuth chloride (BiCl , 98% purity), Antimony chloride (SbCl , 99.95% purity), Tellurium powder (Te,
3
3
99.8% purity), Oleic acid (C H O ), 1-Octadecene (C H , ODE), thioglycolic acid (C H O S, 98%, TGA),
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2
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2
2
4
tri-butyl phosphine (C H P, 93.5%, TBP), acetone and isopropanol were all purchased from Sigma Aldrich
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(Stockholm, Sweden) and used as received without further purification. All chemicals were of analytical
grade.
Synthesis of nanostructured Bi Te and Sb Te powders
2 3 2 3
The synthesis was performed using a MW-assisted thermolysis method. To achieve the desired Bi Te and
2
3
Sb Te compounds, stoichiometric amounts of each precursor were used to maintain a 2:3 molar ratio for
3
2
Bi:Te and Sb:Te. The Te powder was first complexed with TBP (6 mL) by heating the mixture at 220 °C,
using MW power of 400 W under constant stirring using a MW synthesizer (Biotage® Initiator+), until all
the Te powder was fully dissolved. Meanwhile, in a separate vial, a precursor solution of Bismuth (or
Antimony) was prepared by dissolving a stoichiometric amount of BiCl (or SbCl ) in Oleic acid under
3
3
continuous stirring for 30 min. The solution was then transferred to a 100 mL Teflon vessel, where ODE
(8 mL) and TGA (3 mL) were added. The reaction schematics are shown in Figure 1.
Eventually, the mixture was heated by MW (1800 Watt; flexiWAVE-Milestone, high-pressure multivessel
rotor) to the reaction temperature of 220 °C with 4 min ramp time and 2 min dwell time (see
Supplementary Figure 1A). Upon cooling down the solution to room temperature, the synthesized powder
could be separated easily from the reaction mixture by simple decantation, as displayed in
Supplementary Figure 1B. The products were washed once with acetone and twice with isopropanol, then
dried in a vacuum oven at 80 °C for 3 h. Large-scale synthesis has been achieved by performing the same
reaction in parallel in four reactors in a single run. The MW-reactor system, reaction profile and multivessel
reaction possibilities are presented in Supplementary Figure 2.
Consolidation using spark plasma sintering
The powders obtained by the MW-assisted thermolysis method were loaded into a graphite die (Ф 15 mm),
with top and bottom graphite punches, and sintered by Spark Plasma Sintering (SPS, Dr. Sinter 825, Fuji
Electronic Industrial Co. Ltd., Tokyo, Japan) to form nanostructured pellets. The sintering process was
performed at 400 °C under 70 MPa with a heating rate of 30 °C/min and a holding time of 5 min for both
samples. During the cooling process from 400 °C to room temperature, the load was reduced from 70 to
0 MPa. Finally, the pellet was polished to achieve a smooth and decontaminated (from residues of the
graphite die and punches) surface for further analysis. The relative density of the compacted samples was
about 78%.

Structural, morphological, and surface characterization
X-ray powder diffraction analysis
X-ray powder diffraction (XRPD) analysis was accomplished using a Philips PANalytical X'Pert Pro Powder
Diffractometer, equipped with copper anode (Cu-Kα radiation, λ = 1.5406 Å) to identify the crystalline
1
phases present, and the changes in the structure due to sintering. The analysis was done in the continuous
scan mode, with a step size (2θ) of 0.24°, and 0.04°/s as the scan speed. The crystalline phases of the samples
were determined via the High-score Pro software.