Copper chalcogenides have attracted much attention in recent years because of their promising applications in thermoelectric conversion. However, many of them suffer from phase transformation at low temperature. Motivated by the synthesis of bulk β‐CsCu₅Se₃ with high phase transformation temperature of 923 K for photovoltaic applications, its thermoelectric properties using first‐principles calculations combined with Boltzmann transport theory are systematically studied. The results show that β‐CsCu₅Se₃ possesses ultralow lattice thermal conductivities of 0.24, 0.41, and 0.25 W mK⁻¹ along the x, y, and z directions at room temperature, respectively, which are further reduced to 0.09, 0.15, and 0.09 W mK⁻¹ at 800 K. A detailed analysis of its group velocity, three phonon scattering rate, Grüneisen parameter and three phonon phase space reveals that the weak harmonicity and strong phonon anharmonic scattering are responsible for the ultralow lattice thermal conductivity, leading to a high figure of merit (ZT) value of 1.81 along the y direction at 800 K, which is three times higher than that of known thermoelectric materials o‐CsCu₅S₃ (0.46 at 800 K) and t‐CsCu₅S₃ (0.56 at 875 K). This study suggests that β‐CsCu₅Se₃ is a multifunctional material promising for both photovoltaic and thermoelectric applications.

中文翻译：

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β-CsCu5Se3：一种超越光伏应用的有前途的热电材料

硫族铜由于其在热电转换中的应用前景而备受关注。然而，它们中的许多在低温下遭受相变的困扰。通过本体合成动机β -CsCu ₅硒₃具有高的相变温度923的K用于光伏应用来说，使用第一原理计算与玻尔兹曼输运理论结合其热电性能被系统地研究。结果表明，β‐ CsCu ₅ Se ₃沿x，y和b具有0.24、0.41和0.25 W mK ^-1的超低晶格热导率。室温下的z方向分别在800 K下进一步减小到0.09、0.15和0.09 W mK ^-1。对其群速度，三个声子散射速率，Grüneisen参数和三个声子相空间的详细分析表明，弱谐和强声子非谐散射负责超低晶格热导率，导致品质因数（高数字ZT的沿着1.81）值Ý在800K方向，其比已知的热电材料的高三倍ö - CsCu ₅ S ₃（在800 K时为0.46）和t ‐CsCu ₅ S ₃（在875 K时为0.56）。这项研究表明，β -CsCu ₅硒₃是一种多功能材料有前途的两种光伏和热电应用。