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Seo et al. Energy Mater. 2025, 5, 500123 https://dx.doi.org/10.20517/energymater.2025.38 Page 9 of 18

Thermal conductivity measurement
Using the flash diffusivity method, thermal diffusivity was evaluated for the four disk-shaped title
compounds between 323 and 861 K. The measurements were performed with a Netzsch LFA 467
HyperFlash system in an argon environment, where a laser pulse heats the sample's front surface, and an
Infrared (IR) detector tracks the subsequent temperature rise on the back surface. The thermal conductivity
[31]
κ was determined using κ = DC ρ, where D = thermal diffusivity, C = heat capacity, and ρ = density . The
p
p
Dulong-Petit value (3R/atom, R = gas constant) was used for C . The total thermal conductivity κ was
[31]
tot
p
calculated by the sum of the lattice κ and the electronic κ thermal conductivities . The electronic
[32]
elec
latt
thermal conductivity was evaluated using the Wiedemann-Franz law: κ = LσT, where L is the
elec
temperature-dependent Lorenz number, which was derived from the single-parabolic band model using the
temperature-dependent Seebeck coefficient S . Subsequently, the lattice thermal conductivity was
[32]
calculated using: κ = κ - κ .
latt
elec
tot
EDS and EPMA analysis
The elemental composition and distribution within the compounds Ca YbZn Cu Sb , Ca YbZn Cu Sb ,
0.1
8
0.05
9
4.35
9
4.4
8
and Ca YbZn Cu Sb were investigated using EDS. The measurements were carried out using a ULTRA
0.15
8
4.35
9
Plus FE-SEM, with the operating condition set to an acceleration potential of 20 kV. Well-grown single
crystals synthesized via the molten Pb-flux technique were affixed to an aluminum sample holder under an
argon atmosphere. Results from the EDS analysis, presented in Supplementary Figure 3, indicated a
homogeneous distribution of Cu within these single crystals. In particular, the quantitative elemental
analyses of these three title compounds were also conducted by the JEOL JXA-IHP200F EPMA using an
acceleration voltage of 20 KeV with a current of 50 nA in a WDS mode for randomly selected locations.
EPMA analysis resulted in the chemical compositions of Ca Yb 0 . 8 6 Zn 4 . 5 1 Cu 0 . 0 7 Sb ,
8.25
8.81
Ca Yb Zn Cu Sb , and Ca Yb Zn Cu Sb for Ca YbZn Cu Sb , Ca YbZn Cu Sb , and
8.54
4.54
8
0.14
8.69
1.01
8
0.1
4.4
8.11
8.36
9
4.45
9
0.05
1.00
4.49
0.11
Ca YbZn Cu Sb , respectively.
9
4.35
8
0.15
RESULTS AND DISCUSSION
Crystal structure analysis
Seven title compounds in the Ca Yb Zn Cu Sb (0 ≤ x ≤ 1.50, 0 ≤ y ≤ 0.15) system were prepared using the
4.5-y
y
9
x
9-x
molten Pb-flux method. Initial structural assessments, including the determination of phase purities and
lattice parameters of all compounds, were conducted through Rietveld refinements for the collected PXRD
data. As displayed in Figure 2 and Supplementary Figure 1, all seven compounds crystallize as single-phase
products. The refined lattice parameters were consistent with those obtained from SXRD data refinement.
Further detailed structural refinements for one ternary and three quaternary Zn-containing title compounds
were conducted by SXRD analysis, and the resultant crystallographical details are listed in Tables 1-3. The
studied compounds adopted the Ca Mn Bi -type phase having an orthorhombic Pbam space group (Pearson
4
9
9
code oP44, Z = 2) , and thirteen crystallographically independent atomic sites including the five Ca or Ca/
[13]
Yb mixed-sites, three Zn or Zn/Cu mixed-sites, and five Sb sites were refined and presented in Table 2.
However, the detailed chemical compositions of the three quinary compounds containing both Zn and Cu
were not accurately refined using SXRD data since X-ray scattering factors of Zn and Cu were similar.
Instead, the detailed chemical compositions of these compounds were evaluated by EPMA analysis, and the
results are as follows: Ca Yb Zn Cu Sb , Ca Yb Zn Cu Sb and Ca Yb Zn Cu Sb for
8.11
0.11
8.54,
8.69
8.25
1.01
0.07
1.00
8.36
8.81
4.49
0.14
0.86
4.51
4.54
Ca YbZn Cu Sb , Ca YbZn Cu Sb , and Ca YbZn Cu Sb (all nominal compositions).
8
4.4
0.1
9
8
4.45
0.05
4.35
0.15
9
9
8
Since all seven title compounds are isostructural, the detailed overall crystal structure can be explained using
a representative quaternary compound Ca 8.43(2) Yb Zn 4.46(1) Sb in Figure 3. The presented crystal arrangement
9
0.57
can basically be elucidated as an assembly of (1) a complex 2-dimensional (2D) layered anionic structure;
and (2) two different types of electron-donating cationic elements. Interestingly, the 2D anionic layered