Thermoelectric (TE) performance of Ca₃Co₄O₉ (CCO) has been investigated extensively via a doping strategy in the past decades. However, the doping sites of different sublayers in CCO and their contributions to the TE performance remain unrevealed because of its strong correlated electronic system. In this work, Sr and Ti are chosen to realize doping at the [Ca₂CoO₃] and [CoO₂] sublayers in CCO. It was found that figure of merit (ZT) at 957 K of Ti-doped CCO was improved 30% than that of undoped CCO whereas 1 at% Sr doping brought about a 150% increase in ZT as compared to undoped CCO. The significant increase in electronic conductivity and the Seebeck coefficient are attributed to the enhanced carrier concentration and spin-entropy of Co⁴⁺ originating from the Sr doping effects in [Ca₂CoO₃] sublayer, which are evidenced by the scanning electron microscope (SEM), Raman, Hall, and X-ray photoelectron spectroscopy (XPS) analysis. Furthermore, the reduced thermal conductivity is attributed to the improved phonon scattering from heavier Sr doped Ca site in [Ca₂CoO₃] sublayer. Our findings demonstrate that doping at Ca sites of [Ca₂CoO₃] layer is a feasible pathway to boost TE performance of CCO material through promoting the electronic conductivity and the Seebeck coefficient, and reducing the thermal conductivity simultaneously. This work provides a deep understanding of the current limited ZT enhancement on CCO material and provides an approach to enhance the TE performance of other layered structure materials.

在过去的几十年中，已经通过掺杂策略对Ca ₃ Co ₄ O ₉（CCO）的热电（TE）性能进行了广泛的研究。然而，由于其强大的相关电子系统，CCO中不同子层的掺杂位点及其对TE性能的贡献仍然未被揭示。在这项工作中，选择Sr和Ti来实现CCO中[Ca ₂ CoO ₃ ]和[CoO ₂ ]子层的掺杂。发现掺杂Ti的CCO在957 K下的品质因数（ZT）比未掺杂的CCO提高了30％，而1 at％的Sr掺杂带来了ZT的150％的提高。与未掺杂的CCO相比。电子电导率和塞贝克系数的显着提高归因于由[Ca ₂ CoO ₃ ]子层中的Sr掺杂效应引起的Co ^4+的载流子浓度和自旋熵的增强，这由扫描电子显微镜（SEM）证明），拉曼，霍尔和X射线光电子能谱（XPS）分析。此外，降低的热导率归因于来自[Ca ₂ CoO ₃ ]子层中较重的Sr掺杂Ca部位的声子散射的改善。我们的发现表明，在[Ca ₂ CoO ₃]层是通过提高电子传导率和塞贝克系数并同时降低热导率来提高CCO材料的TE性能的可行途径。这项工作深入了解了目前在CCO材料上有限的ZT增强，并提供了一种增强其他层状结构材料的TE性能的方法。