Enhanced Thermoelectric Properties in a New Silicon Crystal Si24 with Intrinsic Nanoscale Porous Structure

TL;DR

This study demonstrates that the newly synthesized silicon allotrope Si24, with intrinsic nanoscale pores, significantly improves thermoelectric efficiency at room temperature by reducing thermal conductivity while maintaining electrical conductivity.

Contribution

The paper provides a first-principles analysis showing that intrinsic nanostructures in Si24 enhance thermoelectric performance without extrinsic modifications.

Findings

Si24 exhibits an order-of-magnitude higher thermoelectric figure of merit than cubic silicon.

Intrinsic nanopores effectively hinder heat conduction while preserving electrical conductivity.

Confined rattling guest atoms can further reduce thermal conductivity.

Abstract

Thermoelectric device is a promising next-generation energy solution owing to its capability to transform waste heat into useful electric energy, which can be realized in materials with high elec- tric conductivities and low thermal conductivities. A recently synthesized silicon allotrope of Si$_{24}$ features highly anisotropic crystal structure with nanometre-sized regular pores. Here, based on first-principles study without any empirical parameter, we show that the slightly doped Si$_{24}$ can pro- vide an order-of-magnitude enhanced thermoelectric figure of merit at room temperature, compared with the cubic diamond phase of silicon. We ascribe the enhancement to the intrinsic nanostructure formed by the nanopore array, which effectively hinders heat conduction while electric conductivity is maintained. This can be a viable option to enhance the thermoelectric figure of merit without further forming an extrinsic nanostructure. In addition, we propose a practical strategy to further diminish the thermal conductivity without affecting electric conductivity by confining rattling guest atoms in the pores.