Thermal Anisotropy Enhanced by Phonon Size Effects in Nanoporous Materials

TL;DR

This study demonstrates how nanoporous materials with anisotropic pore arrangements can induce strong thermal conductivity anisotropy by leveraging phonon size effects, offering new avenues for thermal management and thermoelectric applications.

Contribution

The paper introduces a novel approach using anisotropic nanoporous lattices to control heat transport directionality through phonon size effects, supported by first-principles calculations.

Findings

Strong thermal conductivity anisotropy predicted in nanoporous silicon.

Anisotropic pore arrangements significantly influence phonon transport.

Phonon size effects are crucial for tuning thermal anisotropy.

Abstract

While thermal anisotropicity is a desirable materials property for many applications, including transverse thermoelectrics and thermal management in electronic devices, it remains elusive in practical natural compounds. In this work, we show how nanoporous materials with anisotropic pore lattices can be used as a platform for inducing strong heat transport directionality in isotropic materials. Using density functional theory and the phonon Boltzmann transport equation, we calculate the phonon-size effects and thermal conductivity of nanoporous silicon with different anisotropicpore lattices. Our calculations predict a strong directionality in the thermal conductivity, dictated by the difference in the pore-pore distances along the two Cartesian axes. As the space between pores along the direction of the applied temperature gradient represents the phonon bottleneck, an anisotropic pores lattice distortion induces directionality in heat transport. Using Fourier's law, we also compute diffusive heat transport for the same geometries obtaining significantly smaller anisotropicity, revealing the crucial role of phonon-size effects in tuning thermal transport directionality. Besides enhancing our understanding of nanoscale heat transport, our results demonstrate the promise of nanoporous materials for modulating anisotropy in thermal conductivity.