Thermoelectric properties of Co, Ir, and Os-Doped FeSi Alloys: Evidence for Strong Electron-Phonon Coupling

TL;DR

This study investigates how doping FeSi with transition metals Co, Ir, and Os affects thermoelectric properties, revealing strong electron-phonon coupling and potential for improved thermoelectric performance.

Contribution

It provides new insights into the impact of transition metal dopants on FeSi alloys and demonstrates the significance of electron-phonon interactions on thermal conductivity.

Findings

Maximum ZT increased to 0.08 at 100 K with Ir doping.

Strong electron-phonon coupling invalidates traditional thermal conductivity models.

Grain size reduction further improves ZT to 0.125 at 100 K.

Abstract

The effects of various transition metal dopants on the electrical and thermal transport properties of Fe1-xMxSi alloys (M= Co, Ir, Os) are reported. The maximum thermoelectric figure of merit ZTmax is improved from 0.007 at 60 K for pure FeSi to ZT = 0.08 at 100 K for 4% Ir doping. A comparison of the thermal conductivity data among Os, Ir and Co doped alloys indicates strong electron-phonon coupling in this compound. Because of this interaction, the common approximation of dividing the total thermal conductivity into independent electronic and lattice components ({\kappa}Total = {\kappa}electronic + {\kappa}lattice) fails for these alloys. The effects of grain size on thermoelectric properties of Fe0.96Ir0.04Si alloys are also reported. The thermal conductivity can be lowered by about 50% with little or no effect on the electrical resistivity or Seebeck coefficient. This results in ZTmax = 0.125 at 100 K, still about a factor of five too low for solid-state refrigeration applications.