Layered thermoelectric materials (LTMs) have attracted great attention due to their anisotropic transport behaviors that provide an opportunity to disentangle the interrelated electrical and thermal conductivities. In this study, we found that hexagonal CaAgSb (h-CaAgSb) possesses a lower lattice thermal conductivity and a higher electrical conductivity simultaneously along the in-plane direction when compared with the out-of-plane direction. The low in-plane lattice thermal conductivity mainly originates from the low group velocity of longitudinal acoustic phonon modes. Meanwhile, strong anharmonicity is discovered for the low-lying optical phonon modes. On the other hand, the high in-plane electrical conductivity relies on the small effective mass. Thus, both p-type and n-type h-CaAgSb exhibit a high zT over 2.0 along the in-plane direction at the optimal carrier concentrations. The anisotropic transport properties of h-CaAgSb reported in this work may provide guidance to the experiments. More importantly, the physical insights revealed for the disentangled electrical and thermal transport properties may pave the way for finding other excellent LTMs and optimizing the thermoelectric performance through structure engineering.

中文翻译：

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褶皱层导致六方 CaAgSb 的面内 zT 值较高


层状热电材料 （LTM） 因其各向异性传输行为而引起了极大的关注，这为解开相互关联的导电性和导热性提供了机会。在这项研究中，我们发现与面外方向相比，六方 CaAgSb （h-CaAgSb） 在面内方向上同时具有较低的晶格热导率和较高的电导率。低面内晶格热导率主要源于纵向声学声子模式的低群速度。同时，发现了低洼光学声子模式的强烈不谐性。另一方面，高面内电导率依赖于小的有效质量。因此，在最佳载流子浓度下，p 型和 n 型 h-CaAgSb 沿面内方向均表现出超过 2.0 的高 zT。本工作报道的 h-CaAgSb 的各向异性传输特性可能为实验提供指导。更重要的是，揭示解开的电和热传输特性的物理见解可能为寻找其他优秀的 LTM 和通过结构工程优化热电性能铺平道路。