A unique [Sb₆O₂S₁₃]¹²⁻ finite chain in oxychalcogenide Ba₆Sb₆O₂S₁₃ leading to ultra-low thermal conductivity and giant birefringence

Abstract

Recently, heteroanionic materials have been drawing wide attention due to their unique crystal structures which result in fascinating physical properties. However, reports on structural exploration and functional application of lone-pair-cation-based oxychalcogenides are still very rare. In this work, a new Sb-based oxysulfide, Ba₆Sb₆O₂S₁₃, was successfully obtained via a high-temperature solid-phase method. Ba₆Sb₆O₂S₁₃ belongs to the monoclinic space group of P2₁/c (no. 14) and is formed by charge-balanced Ba²⁺ cations and zero-dimensional (0D) [Sb₆O₂S₁₃]¹²⁻ finite chains made of the triangular-pyramid [SbOS₂], quadrangular-pyramid [SbOS₃] and teeter-totter [SbS₄] units by sharing vertices. Note that the coexistence of various Sb-coordinated fashions in one material is surprisingly found for the first time. More encouragingly, such a unique 0D structure in Ba₆Sb₆O₂S₁₃ leads to an ultra-low thermal conductivity of 0.25 W m⁻¹ K⁻¹ at 700 K (one of the lowest values seen in a crystalline material) and a giant birefringence of 0.66 at 2050 nm (the highest value among metal chalcogenides reported thus far), which is further confirmed using theoretical calculations. As a result, this work will inspire intriguing and further research on heteroanionic materials with low-dimensional structures and hold great potential for their utilization in the photothermal field.

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Introduction

In recent years, low-dimensional inorganic chalcogenides with unique chemical bonding characteristics (ionic, covalent, or van der Waals) have attracted great attention because of their intriguing physical properties, such as photocatalysis, photoluminescence, magnetism, superconductivity, thermoelectricity, and second-order nonlinear optics (NLO).¹ For example, a remarkable photocurrent response was observed in the pentanary chalcogenide Rb₂Ba₃Cu₂Sb₂S₁₀, in which the structure is formed by one-dimensional (1D) [Cu₂Sb₂S₁₀]⁸⁻ chains.² The quaternary sulphide Ba₈Zn₄Ga₂S₁₅ possesses a 1D [Zn₄Ga₂S₁₅]¹⁶⁻ chain structure and exhibits strong yellow photoluminescence emission at 298 K.³ An unprecedented two-dimensional (2D) layered chalcohalide Cs₂[Mn₂Ga₃S₇Cl] displays distinguishing structural features with the coexistence of two Mn-based coordination geometries and exhibits an impressive ferrimagnetic phenomenon below 16 K.⁴ Two typical examples are the discovery of superconductivity in the ternary Bi-based tellurides CsBi₄Te₆ and RbBi_11/3Te₆, whose structures are made of alternately stacked 2D ionic [Bi₄Te₆]⁻ and [Bi_11/3Te₆]⁻ layers, respectively.⁵ Single-crystal SnSe exhibits a high figure of merit (ZT of 2.3 ± 0.3 at 973 K along the c axis) with an extremely low intrinsic thermal conductivity (0.23 ± 0.03 W m⁻¹ K⁻¹ at 973 K) owing to the unique wrinkled 2D layered structure.⁶ More recently, a quaternary non-centrosymmetric (NCS) material SrCdSiS₄, which features a 2D [CdSiS₄]²⁻ layered structure, was reported to exhibit superior IR-NLO comprehensive performances.⁷

In contrast to extensively reported layered 2D and 1D chain chalcogenides, reports on zero-dimensional (0D), e.g. “molecular”, inorganic chalcogenides are very scarce. On one hand, these 0D inorganic chalcogenides are mainly obtained through high-temperature solid-state methods. On the other hand, they have a simple structural composition and show a unique physical performance. For instance, the quaternary selenide Ba₂AsGaSe₅ shows a strong visible-light-induced photocatalytic performance (6.5 times larger than that of titanium dioxide powder (P25)), which can be attributed to the discrete novel [AsGaSe₅]⁴⁻ clusters.⁸ Strong second-harmonic generation (SHG) intensities were observed in the NCS chalcogenides Ba₂₃Ga₈Sb₂S₃₈ and M₂As₂Q₅ (M = Ba, Pb; Q = S, Se), in which the structure is composed of isolated [GaS₄] tetrahedra and [SbS₃] pyramids in the former and multiple discrete [As_xQ_y] anions in the latter.⁹ In the quaternary sulphide Ba₃HgGa₂S₇, the combination of seesaw-like [HgS₂] units and tetrahedral [GaS₄] groups prompts the formation of [Hg₂Ga₄S₁₄]¹²⁻ strings which could increase the polarizability of the crystal structure, thus a large birefringence (0.09@2100 nm) was achieved in this compound.¹⁰

Oxychalcogenides, which combine two different types of anions in one structure (i.e., high electronegativity O²⁻ and low electronegativity Q²⁻), have emerged as a new type of low-dimensional functional material in recent years.¹¹ Despite a great number of reports on novel oxychalcogenides with 1D and 2D structures so far, the exploration of 0D structures, especially for Sb-based oxychalcogenides, is quite limited. Hence, in this work, we take interest in the AE/Sb/O/Q (AE = alkaline-earth metal elements; Q = S, Se) system, hoping to obtain low-dimensional structures. Fortunately, a novel Sb-based oxychalcogenide Ba₆Sb₆O₂S₁₃ with a 0D structure was discovered in this quaternary family. Notably, the [Sb₆O₂S₁₃]¹²⁻ finite chain which is not normally found in inorganic chalcogenides is formed in this structure. Here, we report the solid-state synthesis, crystal structure, thermal transport and optical properties, as well as theoretical calculations of Ba₆Sb₆O₂S₁₃.

Results and discussion

Ba₆Sb₆O₂S₁₃ represents a new combination of the quaternary AE/Sb/O/Q (AE = alkaline-earth metals; Q = chalcogen) system and belongs to the monoclinic space group of P2₁/c (no. 14) [Pearson symbol: mP54; idealized Wyckoff sequence: e¹³a] (Table 1). Its asymmetric unit is made up of 6 Ba, 6 Sb, 2 O and 13 S atoms, which are all at the Wyckoff position of 4e except O1 and O2 at 2a (Table 2). As illustrated in Fig. 1a, the Sb1 atom is coordinated to the 1 O atom and 2 S atoms forming a trigonal planar [Sb1OS₂] basic building unit (BBU) while Sb3 atoms are surrounded by the 1 O atom and 3 S atoms in a distorted teeter-totter [Sb2OS₃] environment. The Sb2 atom shows a common teeter-totter coordination mode with 4 S atoms. It is worth mentioning that the coordination diversity of Sb atoms (i.e., [SbOS₂], [SbOS₃], and [SbS₄]) in a single structure has been discovered for the first time. The Sb–O and Sb–S distances are 2.023–2.085 and 2.393–2.858 Å (Table S1†), respectively, which are comparable to those in the reported Sb-based chalcogenides.¹² The heteroanionic [Sb1OS₂] and [Sb3OS₃] BBUs adopt O-sharing and S4-sharing to form [Sb₂S₄O]⁴⁻ groups, which are further connected by isolated [SbS₄] units resulting in a unique finite [Sb₆O₂S₁₃]¹²⁻ chain (Fig. 1b). The specific distributions of these finite [Sb₆O₂S₁₃]¹²⁻ chains parallel to the a–b plane and b–c plane are shown in Fig. 1c and d, respectively. The charge-balanced Ba²⁺ cations are distributed in the spaces of finite [Sb₆O₂S₁₃]¹²⁻ chains, that possess two different coordination modes, i.e., [BaS₈] and [BaOS₈] polyhedra, with Ba–S distances of 3.110–3.702 Å and Ba–O distances of 2.728–2.802 Å (Fig. S1 and Table S1†). The valence states of Ba, Sb, O, and S atoms are determined as 2+, 3+, 2−, and 2−, respectively, according to BVS calculations.¹³ Actually, there still exist 4 other Sb–S interactions with bond distances of 3.01–3.46 Å, which are much larger than the average Sb–S bond distance (2.65 Å) in the structure of Ba₆Sb₆O₂S₁₃. For this reason, the detailed COHP and ICOHP were applied to the in-depth study of the interaction characteristics between Sb and S.¹⁴ As plotted in Fig. 1e and d, the results of the crystal orbital Hamiltonian population (COHP) and integrated COHP (ICOHP) analyses indicate that the bonding interactions of the short Sb–S bonds (2.38–2.86 Å) are much stronger than those of the long Sb–S bonds (3.01–3.46 Å), which supports the coordination environment of Sb atoms in the above-mentioned structural analysis.

Fig. 1 (a) Coordination modes of [SbOS₂], [SbOS₃] and [SbS₄] BBUs; (b) coordination environment of the [Sb₆O₂S₁₃]¹²⁻ finite chain with marked atom numbers; (c) distribution of 0D finite chains on the ab plane; (d) ball-and-stick representation of the unique 0D finite chain structure of Ba₆Sb₆O₂S₁₃ viewed along the bc plane; (e) the COHP diagram for Sb–S bond distances; (f) ICOHP plotted against Sb–S bond distances.

Table 1 Crystallographic information and refinement results for Ba₆Sb₆O₂S₁₃

a R 1 = ∑||Fo| − |Fc||/∑|Fo|, wR2 = [∑w(Fo^2 − Fc^2)^2/∑w(Fo^2)^2]^1/2.
Empirical formula	Ba6Sb6O2S13
CCDC number	2247687
Formula weight	2003.32
Temperature (K)	293(2)
Crystal size (mm)	0.15 × 0.10 × 0.10
Crystal system	Monoclinic
Space group	P21/c (no. 14)
a (Å)	8.7497(7)
b (Å)	14.2018(8)
c (Å)	11.7822(8)
α (°)	90
β (°)	96.616(5)
γ (°)	90
V (Å^3)	1454.3(2)
Z	2
D c (g cm^−3)	4.575
μ (mm^−1)	14.385
GOOF on F^2	1.052
R 1, wR2 (I > 2σ(I))^a	0.0248, 0.0521
R 1, wR2 (all data)	0.0271, 0.0534
Largest diff. peak and hole (e Å^−3)	1.23, −2.03

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Table 2 The atomic coordinates and equivalent isotropic displacement parameters for Ba₆Sb₆O₂S₁₃

Atom	Wyckff.	x	y	z	U eq/Å^2	BVS
U eq is defined as one third of the trace of the orthogonalized Uij tensor.
Ba1	4e	0.29892(4)	0.13605(3)	0.09160(3)	0.00175(2)	1.96
Ba2	4e	0.59957(4)	0.16259(3)	0.45656(3)	0.00153(2)	1.85
Ba3	4e	0.90869(4)	0.36339(3)	0.28593(3)	0.00165(2)	1.96
Sb1	4e	0.15729(5)	0.39552(3)	0.96110(4)	0.00142(2)	2.87
Sb2	4e	0.80265(5)	0.11340(3)	0.11129(4)	0.00227(2)	3.25
Sb3	4e	0.39253(6)	0.38288(4)	0.22091(4)	0.00293(2)	2.85
O	4e	0.3381(5)	0.3300(3)	0.0620(4)	0.00150(9)	2.01
S1	4e	1	0	0	0.00365(7)	1.91
S2	4e	0.3268(2)	0.4891(2)	0.8539(2)	0.00163(3)	1.68
S3	4e	0.2440(2)	0.2778(2)	0.3231(2)	0.00181(4)	1.93
S4	4e	0.1412(2)	0.4986(2)	0.1287(2)	0.00217(4)	1.64
S5	4e	0.9404(2)	0.2469(2)	0.0440(2)	0.00179(3)	1.91
S6	4e	0.6129(2)	0.2376(2)	0.2100(2)	0.00267(4)	2.05
S7	4e	0.6150(2)	0.0967(2)	0.9479(2)	0.00200(4)	1.91

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It is very interesting to compare the above structures with the previously reported structures of Ba₂Sb₂O₂S₃ ¹⁵ and Ba₂Sb₂O₅.¹⁶ From the perspective of structural chemistry, quaternary Ba₆Sb₆O₂S₁₃ and Ba₂Sb₂O₂S₃ (denoted as Ba₆Sb₆O₆S₉) oxychalcogenides can be considered as derivatives by the partial chemical substitution approach (i.e., partial O is replaced by S atoms) with ternary Ba₂Sb₂O₅ (denoted as Ba₆Sb₆O₁₅) as the structural template (see Fig. 2 for details). They have a similar molecular formula, but they exhibit some significantly different structural features: (i) Ba₂Sb₂O₅ is crystalline in the orthorhombic crystal system, whereas Ba₆Sb₆O₂S₁₃ and Ba₂Sb₂O₂S₃ belong to the monoclinic crystal system; (ii) 1D infinite [Sb₂O₅]⁴⁻ chains are isolated in Ba₂Sb₂O₅, whereas 0D finite [Sb₆O₂S₁₃]¹²⁻ chains and isolated [Sb₂O₂S₃]⁴⁻ clusters are found in Ba₆Sb₆O₂S₁₃ and Ba₂Sb₂O₂S₃, respectively; (iii) compounds Ba₂Sb₂O₅ and Ba₂Sb₂O₂S₃ possess only one type of Sb-based BBU, i.e., [SbO₄] and [SbO₂S], while Ba₆Sb₆O₂S₁₃ shows three different kinds of BBUs, i.e., [SbOS₂], [SbOS₃], and [SbS₄]. Fig. 2 clearly shows the detailed structural evolution from the Ba₂Sb₂O₅ prototype to the derived Ba₂Sb₂O₂S₃ and Ba₆Sb₆O₂S₁₃. In brief, these findings not only enrich the structural library of heteroanionic compounds but also provide a new approach for designing and exploring new low dimensional oxychalcogenides.

Fig. 2 Structural evolutions from (a) ternary Ba₂Sb₂O₅ (denoted as Ba₆Sb₆O₁₅) to quaternary oxychalcogenide (b) Ba₂Sb₂O₂S₃ (denoted as Ba₆Sb₆O₆S₉) and (c) Ba₆Sb₆O₂S₁₃ by the partial chemical substitution approach.

Furthermore, the properties of the title compound together with other previously reported Sb-based oxychalcogenides are briefly analysed, concluded and summarized (see Table S2† for details).^12b,15,17 From the perspective of structural chemistry, their composition can generally be divided into two parts: charge-balanced cations and anionic substructure. The former is mainly composed of alkaline-earth metals (e.g., Ca, Sr, and Ba) as well as a small amount of rare earth elements (e.g., La and Ce) and Pb, while the latter shows diversity in structural dimensions. Structural analysis shows that there are two main types of BBUs for Sb atoms with stereochemically-active-lone-pairs (SCALPs) in the anionic substructure, i.e., monoanionic [SbO_n]/[SbQ_n] (n = 3, 4, and 5) and heteroanionic [SbO_xQ_y] (x + y = 3, 4, and 5) BBUs. Then, these Sb-based BBUs are further connected to each other or other metal-based BBUs to generate 0D molecules, 1D chains, 2D layers, 3D networks or mixed-dimensional structures. As given in Table S2,† all these oxychalcogenides possess high S-to-O ratios and crystallize in low symmetry monoclinic space groups, except for orthorhombic La₆Sb₄O₁₂S₃. Moreover, most of them have a 2D layered structure (ca. 40%). Usually, low-dimensional chalcogenides can be obtained by enhancing the proportion of charge-balanced cations according to the viewpoint of “dimensional reduction”.¹⁸ Actually, this structural law is not followed in this quaternary family, for instance, Ba₂Sb₂O₂S₃, Sr₂Sb₂O₂Se₃, and Sr_3.5Pb_2.5Sb₆O₅Se₁₀, have the same [X/Sb] ratio of 1.0, but their corresponding structural dimensions are 0D, 1D, and 2D, respectively. Similar phenomena can also be observed in other SCALP-based chalcogenide systems.¹⁹

Single crystals of Ba₆Sb₆O₂S₁₃ were obtained by high temperature solid-state reactions of a mixture of BaS, Sb₂O₃ and Sb₂S₃ at 973 K (see the Experimental section in the ESI†). The elemental distributions of Ba : Sb : O : S were determined by EDX mapping as 6 : 6 : 2 : 13 (Fig. 3a and S2†), which are consistent with the results of single-crystal XRD analysis. The experimental powder XRD patterns matched with the simulated ones very well (Fig. 3b), without other impurities being present. UV–Vis–NIR diffuse reflectance spectroscopy was carried out to investigate the optical absorption properties of the title compound. As presented in Fig. 3c, the deduced optical E_g value of Ba₆Sb₆O₂S₁₃ is 1.68 eV, which is obviously smaller than that of the previously reported Ba₂Sb₂O₂S₃ (2.78 eV). Such significant change in the E_g value can be attributed to different O-to-S ratios, that is, the more O atoms are replaced by S atoms, the smaller E_g value is obtained. Moreover, TG and DSC measurements under a N₂ atmosphere indicate that Ba₆Sb₆O₂S₁₃ exhibits no obvious weight loss in the range of 300–1123 K. In addition, the DSC data show only one obvious endothermic peak at around 1017 K in the heating curve and one obvious exothermic peak at 953 K in the cooling curve, which illustrates Ba₆Sb₆O₂S₁₃ is a congruently melting compound (Fig. 3d).

Fig. 3 Experimental characterization of Ba₆Sb₆O₂S₁₃: (a) the SEM image and the corresponding elemental mapping analysis; (b) experimental (blue) and simulated (black) PXRD patterns; (c) the solid-state diffuse-reflectance spectrum; (d) TG diagram (inset: DSC cyclic curves).

In addition, inspired by a recent study that metal chalcogenides containing SCALPs exhibit extremely low intrinsic thermal conductivities,²⁰ we investigated the thermal transmission performance of Ba₆Sb₆O₂S₁₃. As shown in Fig. 4a, the total thermal conductivity (κ_T) of the polycrystalline Ba₆Sb₆O₂S₁₃ sample was measured in the temperature range of 303 to 723 K. It can be clearly seen that the κ_T value of Ba₆Sb₆O₂S₁₃ gradually decreases to an ultra-low value from ∼0.38 W m⁻¹ K⁻¹ (at 303 K) to ∼0.25 W m⁻¹ K⁻¹ (at 723 K) on heating the sample. As is known, the κ_T value is the summation of lattice thermal conductivity (κ_L) and electrical thermal conductivity (κ_E) values.²¹ Since the E_g value of the title compound is large compared with that of classical thermoelectric materials, κ_E can be ignored, which means that the κ_T value of Ba₆Sb₆O₂S₁₃ can be considered as κ_L.²² Moreover, the calculated minimum lattice thermal conductivity (κ_min) of Ba₆Sb₆O₂S₁₃ was estimated using Cahill's model at about 0.27 W m⁻¹ K⁻¹.²³ The reason for Ba₆Sb₆O₂S₁₃ possessing an ultra-low κ_L value can be mainly attributed to the following two aspects: (i) strongly ionic Ba²⁺ cations can decrease the phonon velocity and boost the phonon scattering ratio, and similar examples can also be found in other Ba-based systems;²⁴ (ii) due to the coexistence of multiple BBUs, the highly polarized [SbOS₂] triangular pyramid, [SbOS₃], and the [SbS₄] square pyramid can effectively enhance the lattice anharmonicity.²⁵ Therefore, the low κ_L value for Ba₆Sb₆O₂S₁₃ was verified through experimental measurement and theoretical estimation. Fig. 4b shows the temperature dependence of the κ_L value of Ba₆Sb₆O₂S₁₃ as well as those of some classical thermoelectric materials, including PbSe (∼10.9–4.3 W m⁻¹ K⁻¹),²⁶ CuFeS₂ (∼8.5–2.3 W m⁻¹ K⁻¹),²⁷ CuInTe₂ (∼6.9–1.7 W m⁻¹ K⁻¹),²⁸ ZrNiSn (∼6.1–4.5 W m⁻¹ K⁻¹),²⁹ FeNiSb (∼5.2–3.0 W m⁻¹ K⁻¹),³⁰ CoSb₃ (∼3.6–2.3 W m⁻¹ K⁻¹),³¹ PbTe (∼2.8–1.9 W m⁻¹ K⁻¹),³² SnTe (∼2.0–1.1 W m⁻¹ K⁻¹),³³ BiSbTe (∼2.3–1.5 W m⁻¹ K⁻¹),³⁴ BiCuSeO (∼1.0–0.5 W m⁻¹ K⁻¹)³⁵ and SnSe (∼0.7–0.2 W m⁻¹ K⁻¹)³⁶ for comparison.

Fig. 4 (a) Lattice thermal conductivity (k_L) as a function of temperature for Ba₆Sb₆O₂S₁₃ (the dashed line represents the minimum k_L value calculated within the Cahill model) and (b) comparison of k_L with other reported state-of-the-art thermoelectric materials.

To gain further insight into the relationship between the crystal structure and optical properties, theoretical investigations based on the density functional theory (DFT) were performed on Ba₆Sb₆O₂S₁₃. The electronic band structure along high symmetry points of the first Brillouin zone is plotted as shown in Fig. 5a and S3,† which reveals that Ba₆Sb₆O₂S₁₃ is a direct band-gap semiconductor with an E_g value of 0.98 eV at the G-point. Although this value is smaller than the experimentally obtained value of 1.68 eV, standard exchange–correlation functionals in DFT are well-known for underestimating E_g.³⁷ As shown by the partial density of states (PDOS) in Fig. 5b, O-2p S-3p and Sb-5s/5p states provide dominant contributions to the top of the valence band (VB), while the bottom of the conduction band (CB) of Ba₆Sb₆O₂S₁₃ is mainly constituted by S-3p and Sb-5p states, with little contributions from the O-2p and Ba-4d states. It can be concluded that the E_g of Ba₆Sb₆O₂S₁₃ is determined by [SbOS₂], [SbOS₃], and [SbS₄] BBUs, that is, 0D finite [Sb₆O₂S₁₃]¹²⁻ chains.

Fig. 5 Theoretical calculated results of Ba₆Sb₆O₂S₁₃: (a) calculated band structure; (b) PDOSs; (c) calculated birefringence (Δn); (d) projection of the charge density maps with major contributions in the CBM and VBM sections. Black atoms: Ba; pink atoms: Sb; red atoms: O; yellow atoms: S.

It is generally believed that a large anisotropy of low dimensional structures is beneficial for obtaining a larger Δn value.³⁸ Given that, also the refractive index was recorded and charge density maps were plotted to offer a more intuitive understanding of the structure–activity relationship. As displayed in Fig. 5c, Ba₆Sb₆O₂S₁₃ exhibits a huge Δn value throughout the entire calculation range. Among them, the calculated Δn value is 0.66@2050 nm, greater than those of recently reported low-dimensional chalcogenides with SCALPs, such as RbBiP₂S₆ (Δn_(cal.) = 0.061@2050 nm),³⁹ K₂Ag₃Sb₃S₇ (Δn_(cal.) = 0.165@2050 nm),⁴⁰ Ba₂As₂Se₅ (Δn_(cal.) = 0.249@2050 nm),^9b CsZnAsSe₃ (Δn_(cal.) = 0.301@2050 nm),⁴¹ and CsCu₃SbS₄ (Δn_(cal.) = 0.442@2050 nm),⁴² which indicates that Ba₆Sb₆O₂S₁₃ can be a promising IR birefringent candidate. Additionally, the experimental results also confirmed that the title compound has a wide IR transmission range from 0.75 to 18.3 μm (Fig. S4†). Furthermore, the calculation results based on the visual charge density maps (Fig. 5d) and electron localization function diagram (Fig. S5†) indicate that the synergistic effect of SCALP-based [SbOS₂], [SbOS₃], and [SbS₄] BBUs in the 0D finite [Sb₆O₂S₁₃]¹²⁻ chains of Ba₆Sb₆O₂S₁₃ is the core contribution for obtaining a giant Δn value.

Conclusions

In summary, a novel quaternary Sb-based oxychalcogenide, Ba₆Sb₆O₂S₁₃, has been successfully obtained by a conventional solid-state method at 973 K. The discrete [Sb₆O₂S₁₃]¹²⁻ finite chain, formed by triangular-pyramid [SbOS₂], quadrangular-pyramid [SbOS₃] and teeter-totter [SbS₄] units, is observed for the first time. UV-Vis-NIR spectroscopy measurement shows that Ba₆Sb₆O₂S₁₃ possesses an optical E_g value of 1.68 eV. Benefiting from the ordered arrangement of 0D [Sb₆O₂S₁₃]¹²⁻ finite chains, the title compound exhibits an ultra-low thermal conductivity (0.25 W m⁻¹ K⁻¹ at 700 K) and an ultra-high birefringence (0.66 at 2050 nm). This work offers some new insights on Sb-based heteroanionic materials which would stimulate more exploratory syntheses and further enrich functional oxychalcogenides.

Author contributions

Y.-F. Shi prepared the samples, designed and carried out the experiments. S. H. Zhou and P. F. Liu carried out the theoretical calculations. X.-T. Wu provided discussion on the structure–property relationship of the title compound. H. Lin and Q.-L. Zhu conceived the experiments, analyzed the results and wrote and edited the manuscript. All the authors have approved the final version of the manuscript.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (22175175), the Fujian Science & Technology Innovation Laboratory for Optoelectronic Information of China (2021ZR118), and the Natural Science Foundation of Fujian Province (2022L3092).

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Footnote

† Electronic supplementary information (ESI) available: Additional experimental and theoretical results, together with additional tables and figures. CCDC 2247687. For ESI and crystallographic data in CIF or other electronic format see DOI: https://doi.org/10.1039/d3qi00850a

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