Tadano Terumasa, Gohda Yoshihiro, Tsuneyuki Shinji
Department of Physics, The University of Tokyo, Tokyo 113-0033, Japan.
Department of Materials Science and Engineering, Tokyo Institute of Technology, Yokohama 226-8502, Japan.
Phys Rev Lett. 2015 Mar 6;114(9):095501. doi: 10.1103/PhysRevLett.114.095501. Epub 2015 Mar 4.
We investigate the role of rattling guest atoms on the lattice thermal conductivity of a type-I clathrate Ba_{8}Ga_{16}Ge_{30} by first-principles lattice dynamics. Comparing phonon properties of filled and empty clathrates, we show that rattlers cause tenfold reductions in the relaxation time of phonons by increasing the phonon-phonon scattering probability. Contrary to the resonant scattering scenario, the reduction in the relaxation time occurs in a wide frequency range, which is crucial for explaining the unusually low thermal conductivities of clathrates. We also find that the impact of rattlers on the group velocity of phonons is secondary because the flattening of phonon dispersion occurs only in a limited phase space in the Brillouin zone.
我们通过第一性原理晶格动力学研究了晃动客体原子在I型包合物Ba₈Ga₁₆Ge₃₀晶格热导率中的作用。通过比较填充和空包合物的声子特性，我们表明，晃动原子通过增加声子-声子散射概率，使声子弛豫时间降低了十倍。与共振散射情况相反，弛豫时间的降低发生在很宽的频率范围内，这对于解释包合物异常低的热导率至关重要。我们还发现，晃动原子对声子群速度的影响是次要的，因为声子色散的扁平化仅发生在布里渊区的有限相空间中。
