High-performance Mg3Sb2-based thermoelectrics with reduced structural disorder and microstructure evolution

Mg₃Sb₂-based thermoelectrics show great promise for next-generation thermoelectric power generators and coolers owing to their excellent figure of merit (zT) and earth-abundant composition elements. However, the complexity of the defect microstructure hinders the advancement of high performance. Here, the defect microstructure is modified via In doping and prolonged sintering time to realize the reduced structural disorder and microstructural evolution, synergistically optimizing electron and phonon transport via a delocalization effect. As a result, an excellent carrier mobility of ~174 cm² V^-1 s^-1 and an ultralow <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mrow><mml:mi>κ</mml:mi></mml:mrow> <mml:mrow><mml:mi>l</mml:mi> <mml:mi>a</mml:mi> <mml:mi>t</mml:mi></mml:mrow> </mml:msub> </mml:math> of ~0.42 W m^-1 K^-1 are realized in this system, leading to an ultrahigh zT of ~2.0 at 723 K. The corresponding single-leg module demonstrates a high conversion efficiency of ~12.6% with a 425 K temperature difference, and the two-pair module of Mg₃Sb₂/MgAgSb displays ~7.1% conversion efficiency with a 276 K temperature difference. This work paves a pathway to improve the thermoelectric performance of Mg₃Sb₂-based materials, and represents a significant step forward for the practical application of Mg₃Sb₂-based devices.