Dilute MnBi2Te4-alloying enables high-performance GeTe thermoelectrics

As an attractive lead-free thermoelectric material, GeTe has gained widespread interest. However, the extremely high hole concentration seriously limits the thermoelectric performance of pristine GeTe. In this work, dilute MnBi2Te4-alloying is utilized to synergically optimize electrical- and thermal-transport properties of GeTe for thermoelectric performance improvement. It can not only decrease the precipitation of Ge to optimize carrier concentration, but also promote multi-band convergence to enlarge the density of state effective mass. Furthermore, the MnBi2Te4-alloyed samples also maintain a moderate carrier mobility. In addition, the increased point-defect scattering for phonons leads to the significant reduction in lattice thermal conductivity. Consequently, a high peak thermoelectric figure of merit (ZT) of ∼1.8 at 723 K and a large average ZT of ∼1.0 from 300 to 723 K are achieved in 4% MnBi2Te4-alloyed GeTe, showing the potential of dilute compound alloying to enhance the thermoelectric performance of GeTe by the concurrent regulation of electrical- and thermal-transport properties.