High thermoelectric and mechanical performance in the n-type polycrystalline SnSe incorporated with multi-walled carbon nanotubes

In this study,we introduce multi-walled carbon nanotubes(MWCNTs)in Pb/I co-doped n-type polycrys-tal SnSe to simultaneously improve its thermoelectric and mechanical properties for the first time.The introduced MWCNTs act as the“bridges”to accelerate the electron carrier transport between SnSe grains,leading to significantly increased electrical conductivity from 32.6 to 45.7 S cm^(−1) at 773 K,which con-tributes to an enhanced power factor of∼5.0μW cm^(−1) K^(−2) at this temperature.Although MWCNTs possess high intrinsic thermal conductivities,these MWCNTs,acting as nanoinclusions in the SnSe matrix to form the dense interfaces between SnSe and MWCNTs,provide extra heat-carrying phonon scattering centers,leading to a slightly reduced lattice thermal conductivity of only 0.34 W m^(−1) K^(−2) at 773 K and in turn,a high ZT of∼1.0 at this temperature.Furthermore,the introduced MWCNTs can simultane-ously act as the“binders”to bond adjacent grains,significantly improving the mechanical properties of SnSe by boosting its Vickers hardness from 39.5 to 50.5.This work indicates that our facile approach can achieve high thermoelectric and mechanical properties in n-type SnSe polycrystals with a considerable potential for applying to thermoelectric devices as n-type elements.

Se-alloying reducing lattice thermal conductivity of Ge_(0.95)Bi_(0.05)Te

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.