Fundamental understanding of anharmonic lattice dynamics and heat conductance physics in crystalline compounds is critical for the development of thermoelectric energy conversion devices. Herein, we thoroughly investigate the microscopic mechanisms of thermal transport in CsCuS by coupling the self-consistent phonon (SCP) theory with the linearized Wigner transport equation (LWTE). We explicitly consider both phonon energy shifts and broadening arising from both cubic and quartic anharmonicities, as well as diagonal/non-diagonal terms of heat flux operators in thermal conductivity. Our findings show that the strong anharmonicity of CsCuS primarily arises from the presence of - anti-bonding hybridization between Cu and S atoms, coupled with the random oscillations of Cs atoms. Notably, the competition between phonon hardening described by the loop diagram and softening induced by the bubble diagram significantly influences particle-like propagation, predominantly reflected in group velocity and energy-conservation rule. Additionally, the electrical transport properties are determined by employing the precise momentum relaxation-time approximation (MRTA). At high temperatures, the thermoelectric performance of -type CsCuS reaches its optimum theoretical value of 0.94 along the in-plane direction based on advanced phonon renormalization theory. In striking contrast, the harmonic approximation theory significantly overestimates the thermoelectric efficiency at the same temperatures, rendering it an impractical expectation. Conversely, the first-order renormalization approach leads to a serious underestimation of the thermoelectric properties due to the over-correction of phonon energy. Our study not only reveals the pivotal role of anharmonic lattice dynamics in accurately assessing thermoelectric properties but also underscores the potential thermoelectric applications for novel copper-based chalcogenides.

中文翻译：

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铜基硫属化物 CsCu3S2 热电性能的分层表征：揭示非简谐晶格动力学的作用


对晶体化合物中的非谐晶格动力学和热导物理学的基本了解对于热电能量转换装置的开发至关重要。在此，我们通过将自洽声子（SCP）理论与线性维格纳输运方程（LWTE）相结合，深入研究了 CsCuS 中热输运的微观机制。我们明确考虑了三次和四次非谐性引起的声子能量转移和展宽，以及热导率中热通量算子的对角/非对角项。我们的研究结果表明，CsCuS 的强非谐性主要源于 Cu 和 S 原子之间反键杂化的存在，以及 Cs 原子的随机振荡。值得注意的是，环图描述的声子硬化和气泡图引起的软化之间的竞争显着影响类粒子传播，主要反映在群速度和能量守恒规则上。此外，电传输特性是通过采用精确的动量弛豫时间近似（MRTA）来确定的。在高温下，基于先进声子重正化理论，α型CsCuS的热电性能沿面内方向达到最佳理论值0.94。与此形成鲜明对比的是，谐波近似理论明显高估了相同温度下的热电效率，使其成为不切实际的期望。相反，一阶重整化方法由于声子能量的过度校正而导致热电性质的严重低估。 我们的研究不仅揭示了非谐晶格动力学在准确评估热电性能方面的关键作用，而且还强调了新型铜基硫属化物的潜在热电应用。