Suppression of thermal conductivity by rattling modes in thermoelectric sodium cobaltate.
Suppression of thermal conductivity by rattling modes in thermoelectric sodium cobaltate.
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DOI：
10.1038/nmat3739
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发表时间：
2013-11
期刊：
影响因子：
41.2
通讯作者：
D. Voneshen;K. Refson;E. Borissenko;M. Krisch;A. Bosak;A. Piovano;E. Cemal;M. Enderle;M. Gutmann;M. Hoesch;M. Roger;L. Gannon;A. Boothroyd;S. Uthayakumar;D. Porter;J. Goff
中科院分区：
文献类型：
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作者：
D. Voneshen;K. Refson;E. Borissenko;M. Krisch;A. Bosak;A. Piovano;E. Cemal;M. Enderle;M. Gutmann;M. Hoesch;M. Roger;L. Gannon;A. Boothroyd;S. Uthayakumar;D. Porter;J. Goff
对高电导率和低热导率的需求产生了热电系统的设计冲突，导致考虑具有复杂晶体结构的材料。笼中离子的振动导致低热导率，我们进行了非弹性X射线和中子散射实验，这些实验与我们对热电Na0.8CoO2（具有大周期超结构）的声子色散的第一性原理密度泛函计算非常一致。我们已经直接观察到一个爱因斯坦般的振动模式在低能量，涉及大的非谐位移的钠离子内的多空位团簇。与无空位的NaCoO2相比，这些嘎嘎作响的模式抑制了六倍的热导率。我们的研究结果将指导下一代材料的设计，用于固态冰箱和电力回收。
The need for both high electrical conductivity and low thermal conductivity creates a design conflict for thermoelectric systems, leading to the consideration of materials with complicated crystal structures. Rattling of ions in cages results in low thermal conductivity,,,, but understanding the mechanism through studies of the phonon dispersion using momentum-resolved spectroscopy is made difficult by the complexity of the unit cells. We have performed inelastic X-ray and neutron scattering experiments that are in remarkable agreement with our first-principles density-functional calculations of the phonon dispersion for thermoelectric Na0.8CoO2, which has a large-period superstructure. We have directly observed an Einstein-like rattling mode at low energy, involving large anharmonic displacements of the sodium ions inside multi-vacancy clusters. These rattling modes suppress the thermal conductivity by a factor of six compared with vacancy-free NaCoO2. Our results will guide the design of the next generation of materials for applications in solid-state refrigerators and power recovery.