Beating the amorphous limit in thermal conductivity by superlattices design

TL;DR

This paper demonstrates that carefully designed superlattices can achieve thermal conductivities below the amorphous limit by effectively blocking heat carrier propagation, using molecular dynamics simulations.

Contribution

It introduces a systematic study of superlattice design parameters that can reduce thermal conductivity below the amorphous limit, a novel approach in thermal management.

Findings

Large mass differences in layers lower thermal conductivity.

Weakened interlayer interactions further reduce heat transfer.

Superlattices can surpass the amorphous limit in thermal insulation.

Abstract

The value measured in the amorphous structure with the same chemical composition is often considered as a lower bound for the thermal conductivity of any material: the heat carriers are strongly scattered by disorder, and their lifetimes reach the minimum time scale of thermal vibrations. An appropriate design at the nano-scale, however, may allow one to reduce the thermal conductivity even below the amorphous limit. In the present contribution, using molecular-dynamics simulation and the Green-Kubo formulation, we study systematically the thermal conductivity of layered phononic materials (superlattices), by tuning different parameters that can characterize such structures. We discover that the key to reach a lower-than-amorphous thermal conductivity is to block almost completely the propagation of the heat carriers, the superlattice phonons. We demonstrate that a large mass difference in the two intercalated layers, or weakened interactions across the interface between layers result in materials with very low thermal conductivity, below the values of the corresponding amorphous counterparts.