Metal chalcogenides underpin a wide variety of energy-related applications and are ideal systems for probing lattice dynamics and fundamental transport phenomena. Here we describe the synthesis and transport properties of CsAg₅TeS₂ and its solid solution CsAg₅Te_3–xS_x (x = 1–2), new semiconductors with tunable band gaps ranging from 0.17 to 0.30 eV. CsAg₅TeS₂ has a fully ordered two-dimensional structure that includes a group of Ag atoms in a heteroleptic tetrahedral coordination geometry (AgTe₂S₂). Single-crystal X-ray diffraction indicates that the compounds crystallize in the tetragonal space group P4/mmm, while pair distribution function (PDF) analysis reveals off-centering at the heteroleptic Ag sites, signifying the lower-symmetry I4/mcm space group. The underlying disorder acts as a phonon-blocking mechanism that helps facilitate an ultralow lattice thermal conductivity below 0.40 W·m^–1·K^–1 at ∼300 K , highlighting the importance of local disorder in thermal transport. Density functional theory provides additional insight into the electronic and thermal properties of the materials, which are good candidates for p-type thermoelectrics.

中文翻译：

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二维CsAg ₅ Te _{3– x} S _x半导体：具有动态无序和超低导热率的多阴离子硫族化物

金属硫属化物是各种与能源有关的应用的基础，并且是探测晶格动力学和基本输运现象的理想系统。在这里，我们描述了CsAg ₅ TeS ₂及其固溶体CsAg ₅ Te _{3– x} S _x（x = 1-2），具有可调带隙范围从0.17至0.30 eV的新型半导体的合成和传输性质。CsAg ₅ TeS ₂具有完全有序的二维结构，该结构在杂配四面体配位几何结构（AgTe ₂ S ₂）。X射线单晶衍射表明化合物在四方晶空间群P 4 / mmm中结晶，而成对分布函数（PDF）分析显示在杂合Ag位点处偏心，这表明较低对称性的I 4 / mcm空间团体。潜在的无序充当了声子阻挡机制，有助于促进在〜300 K时低于0.40 W·m ^–1 ·K ^–1的超低晶格热导率，突出了局部无序在热传输中的重要性。密度泛函理论提供了对材料的电子和热学性质的更多见解，这些材料是p型热电学的理想选择。