Grand herringbone architecture securing the high thermoelectric performance of GeTe

This work demonstrates a unique two-stage cooling procedure for synthesizing high-performance thermoelectric (TE) GeTe alloys with a maximum zT value of 2.0 (720 K) without assistance of chemical doping. The efficiency breakthrough stems from the grand herringbone structure resulted from the annealing step intentionally inserted near the phase transition temperature T-c of GeTe when cooling. Compared with the samples prepared by conventional methods, the two-stage cooled GeTe processes not only lower carrier concentrations p (4.7-5.3 x 10(20) cm(-3)) but also higher mobility (similar to 125 cm(2) V-1 s(-1)) that prevent electrical conductivity and TE power factor from declining as p decreases. The twinned domains in the two-stage cooled samples are further analyzed and classified by the compatibility theory. Our calculations show that the twinning structures in the two-stage cooled samples fit well with the compatibility criterion for twin variant selections and are thermodynamically in a stable state. These results not only attest to the efficacy of using the two-stage cooling procedure to manipulate the microstructures of GeTe but also provides a new paradigm for optimizing the performance of GeTe-based TE materials.