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Dimer rattling mode induced low thermal conductivity in an excellent acoustic conductor

https://doi.org/10.1038/s41467-020-19044-w

Qi, Ji; Dong, Baojuan; Zhang, Zhe; Zhang, Zhao; Chen, Yanna; Zhang, Qiang; Danilkin, Sergey; Chen, Xi; He, Jiaming; Fu, Liangwei; et al (December 2020, Nature Communications)

Abstract A solid with larger sound speeds usually exhibits higher lattice thermal conductivity. Here, we report an exception that CuP₂has 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⁻¹K⁻¹at 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.

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