Hopping Time Scales and the Phonon-Liquid Electron-Crystal Picture in Thermoelectric Copper Selenide.

The suppression of transverse phonons by liquidlike diffusion in superionic conductors has been proposed as a means to dramatically reduce thermal conductivity in thermoelectric materials [H. Lui et al. Nat. Mater. 11, 422 (2012)NMAACR1476-112210.1038/nmat3273]. We have measured the ion transport and lattice dynamics in the original phonon-liquid electron-crystal Cu_{2}Se using neutron spectroscopy. We show that hopping time scales are too slow to significantly affect lattice vibrations and that the transverse phonons persist at all temperatures. Substantial changes to the phonon spectrum occur well below the transition to the superionic phase, and the ultralow thermal conductivity is instead attributed to anharmonicity.

在超离子导体中，通过类液体扩散对横向声子的抑制已被提议作为一种大幅降低热电材料热导率的方法[H. Lui等人，《自然·材料》11, 422 (2012)，NMAACR1476 - 112210.1038/nmat3273]。我们使用中子光谱学测量了原始的声子 - 液体电子 - 晶体Cu₂Se中的离子传输和晶格动力学。我们表明，跳跃时间尺度太慢，无法显著影响晶格振动，并且横向声子在所有温度下都持续存在。在向超离子相转变的温度以下，声子谱就发生了显著变化，而超低热导率应归因于非谐性。