High-performance lead-free cubic GeTe-based thermoelectric alloy

The ferroelectric phase transition of GeTe thermoelectric materials caused by the 4s2 lone-pair electrons of Ge2+ leads to the sudden change of thermal expansion coefficient, which severely restrains its practical applications. Herein, we demonstrate a successful way to suppress the ferroelectric phase-transition temperature down to below room temperature in GeTe. Our approach involves LiSbTe2 alloying, where the charge distribution is manipulated to reduce the influence of the stereochemical activity of the cation lone-pair electrons on the crystal structure. LiSbTe2 alloying can also promote multi-band convergence and enhance phonon scattering. Consequently, a superior ZTave of 1.38 within 300—773 K is achieved in cubic (GeTe)0.70(LiSbTe2)0.30 alloys, which is significantly higher than the reported results for room temperature or near-room temperature cubic GeTe systems so far. Moreover, the calculated conversion efficiency of 17% is also the highest among all nontoxic p-type polycrystalline thermoelectric materials. This work takes a solid step forward in the application of GeTe.