Optimization of the random multilayer structure to break the random-alloy limit of thermal conductivity

A low lattice thermal conductivity (kappa) is desired for thermoelectrics, and a highly anisotropic kappa is essential for applications such as magnetic layers for heat-assisted magnetic recording, where a high cross-plane (perpendicular to layer) kappa is needed to ensure fast writing while a low in-plane kappa is required to avoid interaction between adjacent bits of data. In this work, we conduct molecular dynamics simulations to investigate the kappa of superlattice (SL), random multilayer (RML) and alloy, and reveal that RML can have 1-2 orders of magnitude higher anisotropy in kappa than SL and alloy. We systematically explore how the kappa of SL, RML, and alloy changes relative to each other for different bond strength, interface roughness, atomic mass, and structure size, which provides guidance for choosing materials and structural parameters to build RMLs with optimal performance for specific applications. (C) 2015 AIP Publishing LLC.