Se-alloying reducing lattice thermal conductivity of Ge0.95Bi0.05Te

Abstract

l Se-alloying induces dense point defects scatter high-frequency phonons. l Se-alloying induce resonant states strengthen Umklapp phonon scattering. l Approaching low lattice thermal conductivity of ∼0.65 W m −1 K −1 at 723 K. l Approaching a peak figure of merit value of ∼1.6 at 723 K. High lattice thermal conductivity of intrinsic GeTe limits the wide application of GeTe-based thermoelectrics. Recently, the optimization of GeTe-based thermoelectric materials has been focusing on reducing lattice thermal conductivity via strengthening phonon scattering. In this study, we systematically studied thermoelectric properties of Se-alloyed Ge 0.95 Bi 0.05 Te via theoretical calculations, structural characterizations, and performance evaluations. Our results indicate that Se-alloying can induce dense point defects with mass/strain-field fluctuations and correspondingly enhance point defect phonon scattering of the Ge 0.95 Bi 0.05 Te matrix. Se-alloying might also change chemical bonding strength to introduce resonant states in the base frequency of Ge 0.95 Bi 0.05 Te matrix, which can strengthen Umklapp phonon scattering. Finally, a decreased lattice thermal conductivity from ∼1.02 W m −1 K −1 to ∼0.65 W m −1 K −1 at 723 K is obtained in Ge 0.95 Bi 0.05 Te 1- x Se x pellets with increasing the Se content from 0 to 0.3. A peak figure of merit of ∼1.6 at 723 K is achieved in Ge 0.95 Bi 0.05 Te 0.7 Se 0.3 pellet, which is ∼77% higher than that of pristine GeTe. This study extends the understanding on the thermoelectric performance of GeTe.