α-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 α-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 α-MgAgSb with large grain size and less oxygen content, as compared with our ball milled samples. The as-synthesized tantalum-sealing melted α-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 α-MgAgSb. The average power factors and average zT values are also as high as 25 μW 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 α-MgAgSb but also demonstrates its great promise for harvesting low-grade waste heat.

α-MgAgSb凭借其优异的电学性能、超低的晶格热导率和丰富的组成元素被认为是一种潜在的近室温热电材料。然而，由于其复杂的相变和元素Mg的高反应性，很难获得高质量的相纯α-MgAgSb，这掩盖了材料的本征热电性能。在此，通过采用钽密封熔化技术，与我们的球磨样品相比，我们获得了具有大晶粒和低氧含量的高质量纯 α-MgAgSb。合成后的钽封熔 α-MgAgSb 在没有元素掺杂或合金化的情况下，表现出固有的低热导率、大加权迁移率和接近最佳范围的高载流子浓度。最终，在钽密封熔化的 α-MgAgSb 中，zT值在 500 K 左右为 1.3。在(300 - 550) K的低温范围内，平均功率因数和平均zT值也分别高达25 μW cm ^-1 K ^-2和1.1，均在已知材料中名列前茅。这项研究不仅为理解 α-MgAgSb 的内在特性提供了新的思路，而且展示了它在收集低品位废热方面的巨大前景。