Dimer rattling mode induced low thermal conductivity in an excellent acoustic conductor
Ji Qi, Baojuan Dong, Zhe Zhang, Zhao Zhang, Yanna Chen, Qiang Zhang, Sergey Danilkin, Xi Chen, Jiaming He, Liangwei Fu, Xiaoming Jiang, Guozhi Chai, Satoshi Hiroi, Koji Ohara, Zongteng Zhang, Weijun Ren, Teng Yang, Jianshi Zhou, Sakata Osami, Jiaqing He, Dehong Yu, Bing Li, Zhidong Zhang
Abstract
Abstract A solid with larger sound speeds usually exhibits higher lattice thermal conductivity. Here, we report an exception that CuP 2 has a quite large mean sound speed of 4155 m s −1 , comparable to GaAs, but single crystals show very low lattice thermal conductivity of about 4 W m −1 K −1 at room temperature, one order of magnitude smaller than GaAs. To understand such a puzzling thermal transport behavior, we have thoroughly investigated the atomic structures and lattice dynamics by combining neutron scattering techniques with first-principles simulations. This compound crystallizes in a layered structure where Cu atoms forming dimers are sandwiched in between P atomic networks. In this work, we reveal that Cu atomic dimers vibrate as a rattling mode with frequency around 11 meV, which is manifested to be remarkably anharmonic and strongly scatters acoustic phonons to achieve the low lattice thermal conductivity.