Shi Xuemin, Zhao Tingting, Zhang Xinyue, Sun Cheng, Chen Zhiwei, Lin Siqi, Li Wen, Gu Hui, Pei Yanzhong
Interdisciplinary Materials Research Center, School of Materials Science and Engineering, Tongji University, 4800 Caoan Road, Shanghai, 201804, China.
School of Materials Science and Engineering, Materials Genome Institute, Shanghai University, Shanghai, 200444, China.
Adv Mater. 2019 Sep;31(36):e1903387. doi: 10.1002/adma.201903387. Epub 2019 Jul 5.
Advancing thermoelectric n-type Mg Sb alloys requires both high carrier concentration offered by effective doping and high carrier mobility enabled by large grains. Existing research usually involves chalcogen doping on the anion sites, and the resultant carrier concentration reaches ≈3 × 10 cm or below. This is much lower than the optimum theoretically predicted, which suggets that further improvements will be possible once a highly efficient dopant is found. Yttrium, a trivalent dopant, is shown to enable carrier concentrations up to and above ≈1 × 10 cm when it is doped on the cation site. Such carrier concentration allows for in-depth understand of the electronic transport properties over a broad range of carrier concentrations, based on a single parabolic band approximation. As well as reasonably high carrier mobility in coarse-grain materials sintered by hot deforming and fusing of large pieces of ingots synthesized by melting, higher thermoelectric performance than earlier experimentally reported for n-type Mg Sb is found. In particular, the thermoelectric figure of merit, zT, is even higher than that of any known n-type thermoelectric, including Bi Te alloys, within 300-500 K. This might pave the way for Mg Sb alloys to become a realistic material for n-type thermoelectrics for sustainable applications.
推进热电n型MgSb合金既需要有效掺杂提供高载流子浓度，又需要大晶粒实现高载流子迁移率。现有研究通常涉及在阴离子位点进行硫族元素掺杂，所得载流子浓度达到约3×10¹⁹ cm⁻³或更低。这远低于理论预测的最佳值，这表明一旦找到高效掺杂剂，进一步改进将是可能的。钇作为一种三价掺杂剂，当它掺杂在阳离子位点时，能够使载流子浓度达到并高于约1×10²⁰ cm⁻³。基于单抛物线能带近似，这样的载流子浓度有助于深入了解广泛载流子浓度范围内的电子输运性质。通过对熔融合成的大块锭料进行热变形和熔合烧结的粗晶材料中，除了具有相当高的载流子迁移率外，还发现了比早期实验报道的n型MgSb更高的热电性能。特别是，在300 - 500K范围内，热电优值zT甚至高于任何已知的n型热电材料，包括Bi₂Te₃合金。这可能为MgSb合金成为可持续应用的n型热电的实用材料铺平道路。
