初期离子导体：离子受限晶格通过极端非简谐性实现类超离子热导率
Incipient ionic conductors: Ion-constrained lattices achieving superionic-like thermal conductivity by extreme anharmonicity
AI总结：
本研究报道了CsCu_2I_3在限制离子迁移下实现类超离子热传输，通过极端非简谐性获得极低热导率与高稳定性，为离子导体材料设计提供新途径。
摘要：
固态中的类声子液体热传导使超离子导体能够作为高效的热电器件候选材料。虽然离子的类液体运动有效抑制了热导率（κ），但其高迁移率同时会因不理想的离子迁移和随之而来的金属沉积引发材料降解，使得平衡低κ和高稳定性仍然是一个挑战。在此，我们利用同步辐射X射线衍射、非弹性X射线散射和基于机器学习势的模拟，报道了具有初期离子传导的CsCu_2I_3中伴随受限长程离子迁移的类超离子热传输。我们揭示了Cu离子在高温下在CuI_4四面体之间表现出受限迁移，展现出超越常规振动的优势声子极端非简谐性，且可与超离子导体中的情况相媲美。因此，在x方向上实现了遵循κ~ T^{0.17}关系的类玻璃态κ（300 K时约为0.3 W m^{-1} K^{-1}），该方向上的Cu离子迁移比超离子导体低三个数量级。这些结果突显了初期离子导体在同时维持低κ和高稳定性方面的优势，阐明了通过离子迁移限制的热传输机制，并为在离子导体中实现超低热导率铺平了有效途径。
英文摘要：
Phonon liquid-like thermal conduction in the solid state enables superionic conductors to serve as efficient thermoelectric device candidates. While liquid-like motion of ions effectively suppresses thermal conductivity (κ), their high mobility concurrently triggers material degradation due to undesirable ion migration and consequent metal deposition, making it still a challenge to balancing low κand high stability. Here, we report a superionic-like thermal transport alongside restricted long-range ion migration in CsCu_2I_3 with incipient ionic conduction, using synchrotron X-ray diffraction, inelastic X-ray scattering, and machine-learning potential-based simulations. We reveal that the Cu ions exhibit confined migration between CuI_4 tetrahedra at high temperatures, displaying extreme anharmonicity of dominated phonons beyond conventional rattling and comparable to that in superionic conductorsl. Consequently, a glass-like κ(~0.3 W m^{-1} K^{-1} at 300 K) following the relationship of κ~ T^{0.17}, was achieved along the x-direction, where Cu ion migration is three oders of magnitude lower than in superionic conductors. These results highlight the advantage of incipient ionic conductors in simultaneously maintaining both low κand high stability, elucidate the thermal transport mechanism via ion migration constraints, and pave an effective pathway toward ultralow thermal conductivity in ionic conductors.
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