Depending on their bandgaps, mixed metal layered chalcogenides are potential candidates for thermoelectric and photovoltaic applications. Herein, we reported the exploratory synthesis of Sr–Zr–Cu–Q (Q = S/Se) systems, resulting in the identification of two novel quaternary chalcogenides: Sr₃Zr₂Cu₄S₉ and Sr₃Zr₂Cu₄Se₉. These isoelectronic compounds (Sr₃Zr₂Cu₄Q₉) crystallized in two different structural types. The Sr₃Zr₂Cu₄S₉ structure (space group: P) adopted the Ba₃Zr₂Cu₄S₉ structure type with eighteen unique atomic sites: 3 × Sr, 2 × Zr, 4 × Cu, and 9 × S. In contrast, the Sr₃Zr₂Cu₄Se₉ structure (P) represented a unique structure type with nineteen unique atomic positions including one additional Cu site compared to the Sr₃Zr₂Cu₄S₉ structure. The sulfide structure was stoichiometric, whereas the selenide structure was found to be non-stoichiometric with three partially occupied Cu positions. The Sr₃Zr₂Cu₄Q₉ structures consisted of layers with the Sr²⁺ cations occupying the interstitial spaces. In both structures, the Zr atoms occupied distorted octahedral positions. A striking difference between the two structures resulted from the distinct bonding interactions between the Cu and Q atoms. The optical bandgap of polycrystalline Sr₃Zr₂Cu₄S₉ was 1.7(1) eV. Interestingly, resistivity measurements of polycrystalline Sr₃Zr₂Cu₄Se₉ revealed metallic/degenerate semiconducting behavior at low temperatures. The photovoltaic performance of semiconducting Sr₃Zr₂Cu₄S₉ demonstrated ∼24% increment in power conversion efficiency when incorporated into a TiO₂/CdS photoanode due to its narrower bandgap, which increased the light-harvesting ability of the cell. We also explored the theoretical electronic structures, COHP, and Bader charges of the Sr₃Zr₂Cu₄Q₉ structures using DFT calculations.

中文翻译：

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Sr3Zr2Cu4Q9 （Q = S 和 Se）：两种新型层状季元混合过渡金属硫系元素


根据带隙的不同，混合金属层状硫系物是热电和光伏应用的潜在候选者。在此，我们报道了 Sr-Zr-Cu-Q （Q = S/Se） 系统的探索性合成，从而鉴定了两种新型季硫系化合物：Sr₃Zr₂Cu₄S₉ 和 Sr₃Zr₂Cu₄Se₉。这些等电子化合物（Sr₃Zr₂Cu₄Q₉）结晶成两种不同的结构类型。Sr₃Zr₂Cu₄S₉ 结构（空间群：P ）采用 Ba₃Zr₂Cu₄S₉ 结构类型，具有 18 个独特的原子位点：3 × Sr、2 × Zr、4 × Cu 和 9 × S。相比之下，与 Sr₃Zr 2 Cu₄ S 9 结构 （P ） 相比，Sr₃Zr₂Cu₄Se₉ 结构代表了一种独特的结构类型，具有 19 个独特的原子位置，包括一个额外的 Cu 位点结构。硫化物结构是化学计量的，而硒化物结构是非化学计量的，具有三个部分占据的 Cu 位置。 Sr₃Zr₂Cu₄Q₉ 结构由 层组成，其中 Sr²⁺ 阳离子占据间隙空间。在这两种结构中，Zr 原子都占据了扭曲的八面体位置。两种结构之间的显着差异是由于 Cu 和 Q 原子之间不同的键合相互作用造成的。多晶 Sr₃Zr₂Cu₄S₉ 的光学带隙为 1.7（1） eV。有趣的是，多晶 Sr₃Zr₂Cu₄Se₉ 的电阻率测量揭示了低温下的金属/简并半导体行为。半导体 Sr₃Zr₂Cu₄S₉ 的光伏性能在掺入 TiO₂/CdS 光阳极时表现出 ∼24% 的功率转换效率增加，因为它的带隙更窄，这增加了电池的光捕获能力。我们还使用 DFT 计算探索了 Sr₃Zr₂Cu₄Q₉ 结构的理论电子结构、COHP 和 Bader 电荷。