PbTe-based thermoelectric materials are some of the most promising for converting heat into electricity, but their n-type versions still lag in performance the p-type ones. Here, we introduce midgap states and nanoscale precipitates using Ga-doping and GeTe-alloying to considerably improve the performance of n-type PbTe. The GeTe alloying significantly enlarges the energy band gap of PbTe and subsequent Ga doping introduces special midgap states that lead to an increased density of states (DOS) effective mass and enhanced Seebeck coefficients. Moreover, the nucleated Ga2Te3 nanoscale precipitates and off-center discordant Ge atoms in the PbTe matrix cause intense phonon scattering, strongly reducing the thermal conductivity (∼0.65 W m-1 K-1 at 623 K). As a result, a high room-temperature thermoelectric figure of merit ZT ∼0.59 and a peak ZTmax of ∼1.47 at 673 K were obtained for the Pb0.98Ga0.02Te-5%GeTe. The ZTavg value that is most relevant for devices is ∼1.27 from 400 to 773 K, the highest recorded value for n-type PbTe.
Bibliographical noteFunding Information:
This work was supported mainly by the Department of Energy, Office of Science Basic Energy Sciences under Grant DE-SC0014520, DOE Office of Science (sample preparation, synthesis, XRD, TE measurements, TEM measurements, DFT calculations). Z.-Z.L. and Q.Y. gratefully acknowledge the National Natural Science Foundation of China (61728401). This work made use of the EPIC facility of Northwestern University’s NUANCE Center, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205), the MRSEC program (NSF DMR-1720139) at the Materials Research Center, the International Institute for Nanotechnology (IIN), the Keck Foundation, and the State of Illinois, through the IIN. User facilities are supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-06CH11357 and DE-AC02-05CH11231. Access to facilities of high performance computational resources at the Northwestern University is acknowledged. The authors also acknowledge Singapore MOE AcRF Tier 2 under Grant Nos. 2018-T2-1-010, Singapore A*STAR Pharos Program SERC 1527200021 and 1527200022, and the support from FACTs of Nanyang Technological University for sample analysis.
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