A comprehensive understanding of thermal transport is crucial for many applications, including heat dissipation systems, thermal barrier coatings, and harnessing potentials of thermoelectric materials. Here, we report an ultralow thermal conductivity, κ, in a p-type layered chalcogenide, TlCuZrSe₃. Our investigation reveals that the anisotropic values of κ in two perpendicular directions in this compound vary between 0.88 and 0.41 Wm^–1K^–1 and 1.15–0.62 Wm^–1K^–1, respectively, over the temperature range of 295–600 K. The low-temperature specific heat data could only be explained by considering Einstein oscillator terms in addition to the conventional Debye model-based contributions, consistent with the presence of localized Tl¹⁺ rattlers. The unique anisotropic crystal structure of TlCuZrSe₃ and the rattling of Tl¹⁺ ions lead to the generation of low-frequency phonons. These relatively flat optical phonon modes hybridize with acoustic phonons, giving rise to strong anharmonicity and phonon scattering channels. Raman spectroscopy confirms that these low-frequency phonon modes have extremely short lifetimes (∼1 ps), explaining the ultralow κ values, approaching the disordered limit, in this highly crystalline material.

中文翻译：

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接近结晶 TlCuZrSe3 无序极限的超低热导率


全面了解热传递对于许多应用至关重要，包括散热系统、热障涂层和利用热电材料的潜力。在这里，我们报道了 p 型层状硫系化物 TlCuZrSe₃ 中的超低热导率 κ。我们的研究表明，在 295-600 K 的温度范围内，该化合物中 κ 在两个垂直方向上的各向异性值分别在 0.88 和 0.41 ^{Wm-1 K-1} 和 1.15-0.62 ^{Wm-1 K-1} 之间变化。低温比热数据只能通过考虑爱因斯坦振荡器项以及传统的基于德拜模型的贡献来解释，这与局部 Tl¹⁺ 嘎嘎声的存在一致。TlCuZrSe₃ 独特的各向异性晶体结构和 Tl¹⁺ 离子的嘎嘎声导致低频声子的产生。这些相对平坦的光学声子模式与声子杂化，产生强烈的不和谐性和声子散射通道。拉曼光谱证实，这些低频声子模式的寿命极短 （∼1 ps），这解释了这种高度结晶材料中接近无序极限的超低 κ 值。