Decoupling Electrothermal Transport in the YbAl3 Kondo Lattice via Itinerant-Electron Magnetic Fluctuations

Abstract The thermoelectric optimization of metallic heavy-fermion systems, such as the YbAl3 Kondo lattice, is fundamentally constrained by an excessively high electronic thermal conductivity (κE) that stems from an inherently high carrier concentration. Herein, we propose an approach to decouple electrothermal transport in YbAl3 by incorporating the soft magnetic alloy LaFe10.4Co0.8Si1.8 (LFS) as a functional second phase. Our results demonstrate that itinerant-electron magnetic fluctuations arising from the LFS phase near its Curie temperature (TC ≈ 292.5 K) act as a dynamic regulator of the Kondo environment. The incorporation of LFS elevates the Kondo temperature and enhances the Kondo interaction while simultaneously reducing the carrier concentration, resulting in a suppression of electrical conductivity. Crucially, this regulation results in a significant reduction in total thermal conductivity (κ), where the decline in κE accounts for 61% of the κ reduction, highlighting the dominance of electronic transport management in metallic TE systems. Simultaneously, magnetoresistance modeling confirms that strong spin–phonon coupling further curtails the phonon mean free path and reduces the lattice thermal conductivity by 34.9% at 300 K. Consequently, a peak zT of 0.38 is achieved at 300 K for the 0.3 wt % LFS composite, representing a 26.7% improvement over pristine YbAl3. This work provides profound insights into leveraging itinerant-electron magnetic degrees of freedom to transcend the metallic transport bottleneck in advanced heavy-fermion thermoelectric materials.