Achieving High-Performance Ge0.92 Bi0.08 Te 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_0.92 Bi_0.08 Te-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_0.92 Bi_0.08 Te(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.

Keywords: GeTe; LaB 6; electron microscopy; thermoelectric materials.