Inhibiting Mg Diffusion and Evaporation by Forming Mg-Rich Reservoir at Grain Boundaries Improves the Thermal Stability of N-Type Mg 3 Sb 2 Thermoelectrics

• Published in: Small (Weinheim an der Bergstrasse, Germany) Germany), 2024-01, Vol.20 (2), p.e2305670
• Main Authors: Geng, Yang, Li, Zerong, Lin, Zehao, Liu, Yali, Lai, Qiangwen, Wu, Xuelian, Hu, Lipeng, Liu, Fusheng, Yu, Yuan, Zhang, Chaohua
• Format: Article
• Language: English
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.202305670

N-type Mg Sb -based thermoelectric materials show great promise in power generation due to their mechanical robustness, low cost of Mg, and high figure of merit (ZT) over a wide range of temperatures. However, their poor thermal stability hinders their practical applications. Here, MgB is introduced to improve the thermal stability of n-type Mg Sb . Enabled by MgB decomposition, extra Mg can be released into the matrix for Mg compensation thermodynamically, and secondary phases of Mg─B compounds can kinetically prevent Mg diffusion along grain boundaries. These synergetic effects inhibit the formation of Mg vacancies at elevated temperatures, thereby enhancing the thermal stability of n-type Mg Sb . Consequently, the Mg (Sb Bi ) Te (MgB ) sample exhibits negligible variation in thermoelectric performance during the 120-hour continuous measurement at 673 K. Moreover, the ZT of n-type Mg Sb can be maintained by adding MgB , reaching a high average ZT of ≈1.1 within 300-723 K. An eight-pair Mg Sb -GeTe-based thermoelectric device is also fabricated, achieving an energy conversion efficiency of ≈5.7% at a temperature difference of 438 K with good thermal stability. This work paves a new way to enhance the long-term thermal stability of n-type Mg Sb -based alloys and other thermoelectrics for practical applications.