标题： 通过减弱银$_{6}$八面体中的银-银键实现固有类玻璃的热输运 显示英文标题

标题： Realizing Intrinsically Glass-like Thermal Transport via Weakening the Ag-Ag Bonds in Ag$_{6}$ Octahedra

摘要： Crystals exhibiting glass-like and low lattice thermal conductivity ($\kappa_{\rm L}$) are not only scientifically intriguing but also practically valuable in various applications, including thermal barrier coatings, thermoelectric energy conversion, and thermal management. However, such unusual $\kappa_{\rm L}$ are typically observed only in compounds containing heavy elements, with large unit cells, or at high temperatures, primarily due to significant anharmonicity. In this study, we utilize chemical bonding principles to weaken the Ag-Ag bonds within the Ag$_6$ octahedron by introducing a ligand in the bridge position. Additionally, the weak Ag-chalcogen bonds, arising from fully filled $p$-$d$ antibonding orbitals, provide an avenue to further enhance lattice anharmonicity. We propose the incorporation of a chalcogen anion as a bridge ligand to promote phonon rattling in Ag$_6$-octahedron-based compounds. 根据这种设计策略，我们理论上识别了五种基于Ag$_6$八面体的化合物，$A$Ag$_3X_2$ ($A$ = Li, Na, and K; $X$ = S and Se)，这些化合物具有较低的平均原子质量并表现出异常强烈的四声子散射。 因此，这些化合物在宽温度范围内表现出超低的热导率（0.3 $\sim$ 0.6 Wm$^{-1}$K$^{-1}$），且温度依赖性最小（T$^{-0.1}$）。 实验验证确认，在200至550 K的温度范围内，NaAg$_3$S$_2$的$\kappa_{\rm L}$为0.45 Wm$^{-1}$K$^{-1}$。我们的结果明确表明，弱化学键在设计具有玻璃样$\kappa_{\rm L}$的化合物中起着关键作用，突显了化学键工程在实现所需热传导特性方面的有效性。 显示英文摘要

摘要： Crystals exhibiting glass-like and low lattice thermal conductivity ($\kappa_{\rm L}$) are not only scientifically intriguing but also practically valuable in various applications, including thermal barrier coatings, thermoelectric energy conversion, and thermal management. However, such unusual $\kappa_{\rm L}$ are typically observed only in compounds containing heavy elements, with large unit cells, or at high temperatures, primarily due to significant anharmonicity. In this study, we utilize chemical bonding principles to weaken the Ag-Ag bonds within the Ag$_6$ octahedron by introducing a ligand in the bridge position. Additionally, the weak Ag-chalcogen bonds, arising from fully filled $p$-$d$ antibonding orbitals, provide an avenue to further enhance lattice anharmonicity. We propose the incorporation of a chalcogen anion as a bridge ligand to promote phonon rattling in Ag$_6$-octahedron-based compounds. Guided by this design strategy, we theoretically identified five Ag$_6$ octahedron-based compounds, $A$Ag$_3X_2$ ($A$ = Li, Na, and K; $X$ = S and Se), which are characterized by low average atomic masses and exhibit exceptionally strong four-phonon scattering. Consequently, these compounds demonstrate ultralow thermal conductivities (0.3 $\sim$ 0.6 Wm$^{-1}$K$^{-1}$) with minimal temperature dependence (T$^{-0.1}$) across a wide temperature range. Experimental validation confirmed that the $\kappa_{\rm L}$ of NaAg$_3$S$_2$ is 0.45 Wm$^{-1}$K$^{-1}$ within the temperature range of 200 to 550 K. Our results clearly demonstrate that weak chemical bonding plays a crucial role in designing compounds with glass-like $\kappa_{\rm L}$, highlighting the effectiveness of chemical bonding engineering in achieving desired thermal transport properties.