A first-principles study on the intrinsic phonon transport of Cu₂GeSe₃

¹ Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences - Ningbo 315201, China
² Shanghai Ultra-precision Optical Manufacturing Engineering Center, Department of Optical Science and Engineering, Fudan University - Shanghai 200433, China

^(a) hzshao@nimte.ac.cn
^(b) jjun@nimte.ac.cn

Received: 12 May 2016
Accepted: 25 July 2016

Abstract

First-principles calculations are employed to investigate the phonon transport of Cu₂GeSe₃. The lattice thermal conductivities of Cu₂GeSe₃ are reproduced. In Cu₂GeSe₃, the low-frequency phonons lower than 88 cm⁻¹, which comprise of most acoustic modes and a few optical modes, contribute more than 90% to the overall lattice thermal conductivity in Cu₂GeSe₃. According to the calculations of phonon transport, nanostructuring may be an effective way to reduce the lattice thermal conductivity of Cu₂GeSe₃. Particularly, at 300 K, the nanostructuring with length scale 100 nm (10 nm) would possibly reduce the thermal conductivity by more than 40% (80%) for Cu₂GeSe₃. With increase of temperature, the effect of nanostructuring on reducing the lattice thermal conductivity will diminish, due to the decrease in the phonon mean-free path. We further speculate that phonon-band engineering by doping with heavy elements such as Pb may further reduce the lattice thermal conductivity. Our work facilitates deep understanding of the mechanisms of effective reduction of the thermal conductivity by nanostructuring or doping, and helps design better thermoelectric materials.