Achieving High‐Performance Ge_0.92Bi_0.08Te Thermoelectrics via LaB₆‐Alloying‐Induced Band Engineering and Multi‐Scale Structure Manipulation

Abstract In this work, a LaB₆‐alloying strategy is reported to effectively boost the figure‐of‐merit (ZT) of Ge_0.92Bi_0.08Te‐based alloys up to ≈2.2 at 723 K, attributed to a synergy of La‐dopant induced band structuring and structural manipulation. Density‐function‐theory calculations reveal that La dopant enlarges the bandgap and converges the energy offset between the sub‐valence bands in cubic‐structured GeTe, leading to a significantly increased effective mass, which gives rise to a high Seebeck coefficient of ≈263 µV K⁻¹ and in turn a superior power factor of ≈43 µW cm⁻¹ K⁻² at 723 K. Besides, comprehensive electron microscopy characterizations reveal that the multi‐scale phonon scattering centers, including a high density of planar defects, Boron nanoparticles in tandem with enhanced boundaries, dispersive Ge nanoprecipitates in the matrix, and massive point defects, contribute to a low lattice thermal conductivity of ≈0.67 W m⁻¹ K⁻¹ at 723 K. Furthermore, a high microhardness of ≈194 H_v is witnessed in the as‐designed Ge_0.92Bi_0.08Te(LaB₆)_0.04 alloy, derived from the multi‐defect‐induced strengthening. This work provides a strategy for developing high‐performance and mechanical robust middle‐temperature thermoelectric materials for practical thermoelectric applications.