Intrinsically high thermoelectric performance in near-room-temperature ?-MgAgSb materials

alpha-MgAgSb is considered as a potential near-room-temperature thermoelectric material in virtue of its excellent electrical properties, ultralow lattice thermal conductivity and abundant constituent elements. However, it is hard to obtain high-quality phase pure alpha-MgAgSb due to its complex phase transition and high reactivity of element Mg, which cloaks material's intrinsic thermoelectric performance. Herein, through adopting a tantalum -sealing melting technique, we achieved highly-quality pure alpha-MgAgSb with large grain size and less oxygen content, as compared with our ball milled samples. The as-synthesized tantalum-sealing melted alpha-MgAgSb, without element doping or alloying, exhibited intrinsically low thermal conductivity, large weighted mobility, and high carrier concentration closes to the optimum range. Eventually, we attained a maximum thermoelectric figure of merit zT value of 1.3 at around 500 K in the tantalum-sealing melted alpha-MgAgSb. The average power factors and average zT values are also as high as 25 mu W cm-1 K-2 and 1.1 respectively in the low-temperature range of (300 -550) K, both of which rank as top values among the known materials. This study not only sheds new light on the understanding of intrinsic properties of alpha-MgAgSb but also demonstrates its great promise for harvesting low-grade waste heat.