Vacancy defect control of colossal thermopower in FeSb2

TL;DR

This study uncovers how atomic defects and Sb vacancy ordering in FeSb2 influence its colossal thermopower and thermal conductivity, combining experimental and computational methods to reveal defect-induced electronic and phononic effects.

Contribution

It identifies specific atomic defects and vacancy arrangements that control thermopower and thermal conductivity in FeSb2, providing insights for material design.

Findings

Atomic defects cause monoclinic distortion of FeSb2.

Sb vacancy ordering forms conducting pathways.

Defects significantly reduce thermal conductivity.

Abstract

Iron diantimonide is a material with the highest known thermoelectric power. By combining scanning transmission electron microscope study with electronic transport neutron, X-ray scattering and first principle calculation we identify atomic defects that control colossal thermopower magnitude and nanoprecipitate clusters with Sb vacancy ordering which induce additional phonon scattering and substantially reduce thermal conductivity. Defects are found to cause rather weak but important monoclinic distortion of the unit cell Pnnm to Pm. The absence of Sb along [010] for high defect concentration forms conducting path due to Fe d orbital overlap. The connection between atomic defect anisotropy and colossal thermopower in FeSb2 paves the way for the understanding and tailoring of giant thermopower in related materials.