We synthesized a new series of layered copper oxytellurides Sr₂TMCu₂Te₂O₂ with variation in transition metal (TM = Mn, Co, and Zn) elements. These compounds are the first example having alternately stacked anti-fluorite Cu₂Te₂ and perovskite-like TM-oxide layers. Owing to the longer ionic radius of Te compared to those of Se and S, they exhibit larger lattice parameters than isostructural sulfides and selenides. First principles band structure calculation for the Zn compound as a representative reveals a semiconducting direct band gap of ∼1.7 eV and the Co compound shows a comparable band gap in the diffuse reflectance measurement result. From the thermoelectric property study, we determined a power factor of ∼70 μW m⁻¹ K⁻² and a figure of merit ZT of ∼0.045 at 770 K for the Co compound, which encourages further improvement in thermoelectric response by applying various enhancement methods. In terms of the magnetic properties, a signature of antiferromagnetic order is observed in the Co and Mn compounds. The present results not only highlight the structural flexibility of the system to tune the physical properties but also suggest that the replacement of the blocking layer can be a new way to improve the thermoelectric performance of layered copper oxychalcogenides.

中文翻译：

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层状羟基氧化碲化物Sr ₂ TMCu ₂ Te ₂ O ₂（TM = Mn，Co，Zn）的合成和物理性能†

我们合成了一系列新的层状氧氧化碲铜Sr ₂ TMCu ₂ Te ₂ O _2，其中过渡金属元素（TM = Mn，Co和Zn）有所不同。这些化合物是具有交替堆叠的抗萤石Cu ₂ Te ₂的第一实例和钙钛矿状的TM氧化物层。由于Te的离子半径比Se和S的离子半径长，因此它们比同构结构的硫化物和硒化物具有更大的晶格参数。以Zn化合物为代表的第一原理能带结构计算显示出约1.7 eV的半导体直接带隙，而Co化合物在漫反射率测量结果中显示出可比的带隙。根据热电特性研究，我们确定了约70μWm ^-1 K ^-2的功率因数和品质因数ZT对于Co化合物，在770 K时约为0.045，这有助于通过应用各种增强方法进一步改善热电响应。就磁性而言，在Co和Mn化合物中观察到反铁磁序的特征。目前的结果不仅突显了系统调节物理性能的结构灵活性，而且暗示了阻挡层的替代可以成为改善层状氧化硫铝酸铜的热电性能的新途径。