Approaching the alloy limit of thermal conductivity in single-crystalline Si-based thermoelectric nanocomposites: A molecular dynamics investigation.

Ruiqiang Guo,Baoling Huang

doi:10.1038/srep09579

Abstract

Single-crystalline Si-based nanocomposites have become promising candidates for thermoelectric applications due to their prominent merits. Reducing the thermal conductivity κ without deteriorating the electrical properties is the key to improve their performance. Through non-equilibrium molecular dynamics simulations, we show that κ of single-crystalline Si-based nanocomposites can be reduced to the alloy limit by embedding various nanoinclusions of similar lattice constants but different lattice orientations or space symmetries with respect to the matrix. The surprisingly low κ is mainly due to the large acoustic phonon density of states mismatch caused by the destruction of lattice periodicity at the interfaces between the nanoinclusions and matrix, which leads to the substantial reduction of phonon group velocity and relaxation time, as well as the enhancement of phonon localization. The resulting κ is also temperature-insensitive due to the dominance of boundary scattering. The increase in thermal resistance induced by lattice structure mismatch mainly comes from the nanoinclusions and the channels between them and is caused by the enhanced boundary scattering at the interfaces parallel to the heat flux. Approaching the alloy limit of κ with potentially improved electrical properties by fillers will remarkably improve ZT of single-crystalline Si-based nanocomposites and extend their application.

Highlights

Through non-equilibrium molecular dynamics simulations, we show that k of single-crystalline Si-based nanocomposites can be reduced to the alloy limit by embedding various nanoinclusions of similar lattice constants but different lattice orientations or space symmetries with respect to the matrix
We investigate k of single-crystalline Si-based nanocomposites using nonequilibrium molecular dynamics (NEMD) simulations and conduct a systematic phonon transport analysis in both frequency domain and real space domain
We calculated k using NEMD with a typical simulation domain shown in Fig. 1(b) and the modified embedded atom method (MEAM) potentials[23], which have been successfully applied to describe a wide range of materials, in particular semiconductors such

Summary

COMPUTATIONAL METHODS THERMOELECTRICS

Approaching the alloy limit of thermal conductivity in single-crystalline Si-based thermoelectric nanocomposites: A molecular dynamics investigation. Through non-equilibrium molecular dynamics simulations, we show that k of single-crystalline Si-based nanocomposites can be reduced to the alloy limit by embedding various nanoinclusions of similar lattice constants but different lattice orientations or space symmetries with respect to the matrix. Yang et al.[16,17] predicted a ZT as high as 0.76 at 300 K for n-type threewww.nature.com/scientificreports dimensional Si phononic crystals, in which k can be reduced by a factor up to 500 with little deterioration in the electrical properties compared with those of bulk Si. With a similar structure, Si-based nanocomposites have rarely been experimentally investigated for thermoelectric applications. To further the understanding of k reduction in these nanocomposites, the local real-space thermal transport and resistance distribution in the Ge/Si nanocomposites are illuminated and the correlation between the enhanced scattering and the surface vibration states is discussed

Results

Discussion

Method