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Seo et al. Energy Mater. 2025, 5, 500123 https://dx.doi.org/10.20517/energymater.2025.38 Page 3 of 18

EXPERIMENTAL
Synthesis
Sample preparation was carried out within an argon-filled glovebox, where oxygen and moisture
concentrations were kept below 0.1 ppm, or under vacuum. All reactants were bought from Alfa Aesar, and
these included Ca (shot, 99.5%), Yb (ingot, 99.9%), Zn (shot, 99.99%), Cu (shot, 99.5%), Sb (shot, 99.9999%),
and Pb (granules, 99.99%). The surfaces of Ca and Yb, which had become tarnished, were scrubbed using a
metal brush inside an argon-filled glovebox before use. All reactant sets were introduced into alumina
crucibles, accompanied by an excess quantity of Pb metal used as the metal-flux in the following ratios:
Ca:Yb:Zn:Cu:Sb:Pb = 9:0:4.5:0:9:45, 8.5:0.5:4.5:0:9:45, 8:1:4.5:0:9:45, 7.5:1.5:4.5:0:9, 8:1:4.45:0.05:9:45,
8:1:4.4:0.1:9:45, and 8:1:4.35:0.15:9:45. Individual alumina crucibles were inserted into separate fused-silica
tubes which were subsequently sealed under vacuum conditions to prevent oxidation of reactants during
processing at elevated temperatures. Then, the reactants were annealed in a furnace ramped up to 1323 K at
200 K/h, kept there for 24 h, and then cooled down to 873 K at a rate of 5 K/h in 90 h. Afterward, the
reaction ampoule was quickly taken out of the furnace and centrifuged for 3 min to separate the crystallized
products from the molten Pb-metal flux. A small amount of remaining Pb metal after the centrifugation was
further dissolved by soaking crystals in H O for 48 h, and the needle/bar-shaped nicely grown single
2
2
crystals were eventually obtained as shown in Figure 1.

Four of the title compounds were additionally prepared via ball-milling followed by a hot-pressing method
to obtain larger quantities of samples suitable for TE property measurements. Initially, each reactant
mixture corresponding to the target composition was placed into a stainless-steel container along with two
0.5-inch and two 0.25-inch stainless-steel balls inside an argon-filled glovebox. The mixtures were then ball-
milled using a SPEX 8000M milling machine for 3 h. During this procedure, milling was paused every
30 min to scrape and thoroughly remix the powders, ensuring sample homogeneity. After completion of
ball-milling, the resulting powdered products were consolidated into disk-shaped samples by hot-pressing
under the following conditions: first at 623 K under 60 MPa for 2 h, and secondly at 1,073 K under the same
pressure for an additional 2 h.

X-ray diffraction analysis
PXRD analysis was initially used to evaluate the phase purity of the five title compounds in the
Ca Yb Zn Cu Sb system (0.57(2) ≤ x ≤ 1.28(2), 0 ≤ y ≤ 0.15). The diffraction data were collected using a
4.5-y
9-x
x
y
9
Bruker D8 diffractometer with monochromatic Cu K radiation (λ = 1.54059 Å). The data acquisition was
α1
conducted for 30 min per sample, utilizing a step size of 0.02°, covering the angular range of 20° ≤ 2θ ≤ 80°.
The phase purities were first examined by comparing the measured diffraction patterns with a calculated
pattern based on the SXRD refinement results of Ca Zn 4.48(2) Sb ; this comparison is shown in Figure 2. In
9
9
addition, the Rietveld refinement was conducted for the collected PXRD patterns of three Zn/Cu mixture-
containing quinary compounds using PDXL2 software to obtain the lattice parameters and volumes of the
unit cells. The refinement results and lattice parameters are presented in Supplementary Table 1 and
Supplementary Figure 1.

SXRD data was collected at room temperature for one ternary and three quaternary compounds:
Ca Zn 4.48(2) Sb , Ca 8.42(2) Yb Zn 4.46(1) Sb , Ca 8.01(3) Yb Zn 4.46(1) Sb , and Ca 7.72(2) Yb Zn 4.45(2) Sb . The measurements
9
0.99
9
1.28
9
9
9
0.57
were performed using a Bruker SMART APEX2 CCD-based diffractometer with Mo K radiation
α1
(λ = 0.71073 Å). Several single crystal specimens were initially screened for quality, and the most suitable
specimen was selected for a thorough analysis using Bruker's APEX2 program . Data reduction,
[20]
integration, determination of unit cell parameters, and atomic site refinement were performed using the