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Page 10 of 18 Seo et al. Energy Mater. 2025, 5, 500123 https://dx.doi.org/10.20517/energymater.2025.38

Figure 3. (A) A crystal structure of Ca Yb Zn Sb illustrated by a combination of ball-and-stick and polyhedral
8.43(2) 0.57 4.46(1) 9
representations viewed down from the c-axis direction. (B) A schematic presentation of the assembly of the 2D anionic layered
structure. Color codes: A (Ca/Yb mixed-site): gray; Zn: orange; Sb: blue.

structure can be built up from its basic building block of the [ZnSb ] tetrahedron, which initially forms the
4
1D [ZnSb ] chains propagating along the c-axis direction by sharing Sb2 with its neighboring tetrahedra
3
[Figure 3B]. These 1D chains are linked together via Sb4 to build the [Zn Sb ] double chains. Then, two
2
5
such double chains are further joined via Sb5 in the form of the inversion symmetry resulting in building
the [Zn Sb ] cluster.
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4
Finally, these anionic clusters are connected to one another via the bridging Zn1 along the a-axis directions
to complete the complete 2D layered structure. In particular, these two different types of Zn sites were
refined in this anionic framework with distinctive local coordination geometries and different occupations:
(1) the Zn1 site (Wyckoff 4h) was located at the center of the trigonal planar site with a partial occupation of
ca. 24%; and (2) the Zn2 and Zn3 (both Wyckoff 4g) were found to be at the center of the tetrahedral site
with full occupations. Interestingly, the Zn1 site showed a rather larger atomic displacement parameter
(ADP) value than two other Zn sites as given in Table 2. This kind of large ADP value was already reported
in other isotypic Ca Mn Bi -type compounds, including Ca Zn 4.10(1) Bi , Sr Cd 4.49(1) Sb , Ca Zn 4.478(8) Sb , and
9
9
9
9
9
4
9
9
9
Yb Zn 4.380(12) Sb 9 [33,34] . Thus, it can be considered as an intrinsic structural feature of the title phase due to the
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partial Zn1 occupation. Furthermore, based on the Zintl-Klemm concept, we could rewrite the chemical
0
2-
1-
2-
1-
2+
formula of the title compounds as: [(Ca/Yb) ] [(4b-Zn ) (3b-Zn )(1b-Sb ) (2b-Sb ) (3b-Sb ) ]. Therefore,
13
2
3
18
8
we believe that the 1/4 occupation at the Zn1 site as shown in the formula should occur to optimize the
overall charge balance between cations and anions. In addition, the charge balance evaluation based on the
coordination geometry is also nicely supported by the ELF analysis, which will be explained further in the
Electronic Structure Analysis section.
Five different types of cationic sites existed in the title system (See Figure 4): (1) the two intra-layer A3 and
A5 sites located inside the “channel-like” voids within the anionic 2D layers; and (2) the three inter-layer
A1, A2, and A4 sites situated in-between two such neighboring 2D layers as displayed in Figure 3. All these
cationic sites were primarily coordinated by six Sb, which formed a slightly distorted octahedral geometry,
and depending on the given local coordination environment, some of the triangular faces were capped by