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Hamawandi et al. Energy Mater. 2025, 5, 500065 https://dx.doi.org/10.20517/energymater.2024.204 Page 9 of 20

XPS analysis
XPS analysis has been used to investigate the surface chemical composition of Bi Te and Sb Te samples. A
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summary of the analysis results is presented in Table 1 and graphically in Figure 5, showing that all analyzed
surfaces contain a specific amount of carbon and other elements - as listed in the table. The percentages of
individual carbon bonds in the two samples are comparable: C-C bond (~60%), C-O (~22%), C-O=C
(~10%), and carbonate (~8%) [Figure 5C and F]. In the case of tellurium, metallic Te residues and mixtures
of TeO (TeO and TeO ) or Te(OH) were detected [Figure 5B and E]. Bi was present on the surface of
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Bi Te only in the form of Bi O oxide [Figure 5A]. In the case of Sb, only the Sb 3d area was quantitatively
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analyzed. Figure 5D shows an example of deconvolution that can be performed to separate the Sb 3d area
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from the O 1s region. Using this approach, the residues of individual Sb compounds were identified.
We have earlier reported on the surface chemistry of Bi Te samples synthesized through hydrothermal and
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polyol routes . A quick comparison of the surface chemistry of as-made Bi Te through thermolysis with
[3]
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similar materials obtained through wet-chemical synthesis would help understand the process of inherited
minute differences in surface speciation. Nanoparticles synthesized through the thermolysis route reveal a
much higher content of organics (70.44% C) when compared to polyol (39.6% C) and hydrothermal
(61.53% C) samples. Oxygen content (23.5%) is also higher than the polyol (22.29%) and hydrothermal
(16.24%) samples. Another striking difference is observed in the speciation of Te, where the thermolysis
sample possesses a higher amount of Te in oxide and hydroxide phases, with the presence of a significant
amount of TeO , TeO , and Te(OH) phases, of which TeO and Te(OH) phases were not observed in the
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polyol and hydrothermal samples.
Local atomic structure and dynamics
The local atomic structure of the as-synthesized Bi Te and Sb Te samples was studied using XAS. Figure 6
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displays the experimental EXAFS spectra χ(k)k of both samples and their corresponding Fourier transforms
(FTs) at the Bi L -edge and Sb/Te K-edges. At temperatures close to 300 K, the amplitude of EXAFS spectra
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is significantly reduced due to the large thermal disorder. Cooling down to 10 K significantly suppresses the
thermal contribution that results in higher EXAFS amplitude and more pronounced FT peaks, revealing
rich information on the local structure up to at least 8 Å. While the analysis of distant coordination shells is
a challenging task using traditional methods, the RMC/EA method [43,50] provides a robust approach in this
case. However, data analysis should be conducted cautiously, especially at elevated temperatures, where the
experimental EXAFS spectra are strongly damped due to thermal disorder.
The RMC/EA simulations resulted in good agreement between experimental and calculated EXAFS spectra
in both k- and R-spaces at all temperatures for Sb Te [Supplementary Figure 4A] and Bi Te
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[Supplementary Figure 4A and B]. It is important to note that a single structural model was derived for each
sample by optimizing the agreement between the Morlet WTs [Supplementary Figure 4C and D] of the
experimental and calculated EXAFS spectra simultaneously at two absorption edges (Sb/Bi and Te). In all
RMC/EA simulations, the structural model aligns with the rhombohedral crystal structure with the space
group R m . At elevated temperatures, contributions from the nearest coordination shells dominate
[44]
EXAFS, FT, and WT signals. However, at lower temperatures, contributions from outer shells become
noteworthy. Indeed, at 10 K, the FT peaks at about 4 Å exhibit the highest intensity for both Sb and Te
K-edges in Sb Te and correspond to Sb-Sb and Te-Te scattering paths, respectively. Additionally, among
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many other structural peaks, a substantial contribution is apparent at about 6 Å (also seen as bright spots in
WT [Supplementary Figure 4C]). Also, in the case of Bi Te , the layered structure gives rise to several
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d i s t i n g u i s h a b l e s t r u c t u r a l p e a k s , w h i c h a r e w e l l o b s e r v e d a t l o w t e m p e r a t u r e s
[Supplementary Figure 4B and D].