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Boosting the Thermoelectric Performance of α-MgAgSb through Phase-Transition-Induced Self-Doping

Kaiwei Guo1,2,*, Tianyu Wang3,*, Zhen Fan1, Lunhua He1,5, Fuhong Chen1,4, Yi Wang1,2, Qi Zhao1, Jiawei Yang1, Hangtian Zhu1 et al.

Jun Li1,†, Te-Huan Liu3,‡, and Huaizhou Zhao1,§

  • *These authors contributed equally to this work.
  • †Contact author: junli@iphy.ac.cn
  • ‡Contact author: thliu@hust.edu.cn
  • §Contact author: hzhao@iphy.ac.cn
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Phys. Rev. X 16, 021011 – Published 10 April, 2026

DOI: https://doi.org/10.1103/gqjx-6kqr

Abstract

In thermoelectric (TE) and other functional electronic materials, chemical doping is commonly employed to tune the carrier density toward an optimal Fermi level and, in turn, maximize the electrical transport. However, in some systems, such as the emerging high-performance p-type TE material α-MgAgSb, chemical doping is challenging due to its weak chemical bonds and extremely low solubility of heteroatomic dopants, which makes it difficult to increase the hole carrier density and realize the otherwise predictable improvements in the TE power factor. Here, we report a doping-free strategy to enhance the TE performance of α-MgAgSb by utilizing a phase-transition-induced self-doping process. Annealing at the phase-transition temperature of 593 K lowers the formation energy of Ag vacancies in the high-temperature β phase, and these vacancies are subsequently retained upon cooling back to the α phase. As a result, the hole concentration increases markedly from 4.5×1019 to 1.3×1020  cm−3, activating multiple valence bands and boosting the room-temperature power factor by ∼35% to 30  μW cm−1 K−2. A single-leg device fabricated from the optimized material achieves a high conversion efficiency of 10.7% and a maximum output power of 71.1 mW at ΔT=285  K. This work demonstrates a viable pathway for enhancing TE performance via phase-transition engineering.

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Popular Summary

Thermoelectric materials, which convert waste heat into usable electricity, are important for sustainable energy applications. Chemical doping is widely used to optimize their electrical transport, but is extremely challenging for high-performance thermoelectric α-MgAgSb because of its weak chemical bonds and low dopant solubility. This long-standing difficulty has restricted further improvements in its thermoelectric properties. We used phase-transition engineering as a doping-free approach. Using controlled annealing near the phase-transition temperature creates stable intrinsic vacancies that act as natural self-doping centers, efficiently tuning carrier transport and boosting thermoelectric performance. This resolves the doping challenge in α-MgAgSb and offers a widely applicable strategy for optimizing other functional materials with similar constraints. This provides a new route for designing efficient thermoelectric devices and advancing practical waste heat recovery technologies.

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References (58)

  1. G. Jeffrey Snyder and Eric S. Toberer, Complex thermoelectric materials, Nat. Mater. 7, 105 (2008).
  2. Jian He and Terry M. Tritt, Advances in thermoelectric materials research: Looking back, and moving forward, Science 357, eaak9997 (2017).
  3. Jun Mao, Hangtian Zhu, Zhiwei Ding, Zihang Liu, Geethal Amila Gamage, Gang Chen, and Zhifeng Ren, High thermoelectric cooling performance of n-type Mg3Bi2-based materials, Science 365, 495 (2019).
  4. Cheng Chang, Minghui Wu, Dongsheng He, Yanling Pei, Chaofeng Wu, Fangyuan Zhu, Yue Chen, Kedong Wang, Li Huang, Jing-feng Li, Jiaqing He, and Lidong Zhao, 3D charge, and 2D phonon transports leading to high out-of-plane ZT in n-type SnSe crystals, Science 360, 778 (2018).
  5. Xiaofan Zhang, Hangtian Zhu, Xuejuan Dong, Zhen Fan, Yuan Yao, Nan Chen, Jiawei Yang, Kaiwei Guo, Jiazheng Hao, Lunhua He, Guodong Li, and Huaizhou Zhao, High-performance MgAgSb/Mg3(Sb,Bi)2-based thermoelectric with η=12% at T≤583  K, Joule 8, 3324 (2024).
  6. Airan Li, Longquan Wang, Xinzhi Wu, Jiankang Li, Xinyuan Wang, Gang Wu, Zhao Hu, and Takao Mori, Semiconductor-metal transition powers high-efficiency MgAgSb thermoelectrics, Sci. Adv. 11, eadx7115 (2025).
  7. Zhonglin Bu, Xinyue Zhang, Yixin Hu, Zhiwei Chen, Siqi Lin, Wen Li, Chong Xiao, and Yanzhong Pei, A record thermoelectric efficiency in tellurium-free mudules for low-grade waste heat recovery, Nat. Commun. 13, 237 (2022).
  8. Qingyu Yan and Mercouri G. Kanatzidis, High-performance thermoelectrics, and challenges for practical devices, Nat. Mater. 21, 503 (2022).
  9. Rigui Deng, Xianli Su, Shiqiang Hao, Zheng Zheng, Min Zhang, Hongyao Xie, Wei Liu, Yonggao Yan, Chris Wolverton, Ctirad Uher, Mercouri G. Kanatzidis, and Xinfeng Tang, High thermoelectric performance in Bi0.46Sb1.54Te3 nanostructured with ZnTe, Energy Environ. Sci. 11, 1520 (2018).
  10. Bed Poudel, Qing Hao, Yi Ma, Yucheng Lan, Austin Minnich, Bo Yu, Xiao Yan, Dezhi Wang, Anderw Muto, Daryoosh Vashaee, XiaoYuan Chen, Junming Liu, Mildred S. Dresselhaus, Gang Chen, and Zhifeng Ren, High-thermoelectric performance of nanostructured bismuth antimony telluride bulk alloys, Science 320, 634 (2008).
  11. Feng Hao, Pengfei Qiu, Yunshan Tang, Shengqiang Bai, Tong Xing, Hsu-Shen Chu, Qihao Zhang, Ping Liu, Tiansong Zhang, Dudi Ren, Jikun Chen, Xun Shi, and Lidong Chen, High efficiency Bi2Te3-based materials, and devices for thermoelectric power generation between 100, and 300 °C, Energy Environ. Sci. 9, 3120 (2016).
  12. Pedersen, Hao Yin, Le Thanh Hung, and Bo Brummerstedt Iversen, Discovery of high-performance low-cost n-type Mg3Sb2-based thermoelectric materials with multi-valley conduction bands, Nat. Commun. 8, 13901 (2016).
  13. Nan Chen, Hangtian Zhu, Guodong Li, Zhen Fan, Xiaofan Zhang, Jiawei Yang, Tianbo Lu, Qiulin Liu, Xiaowei Wu, Yuan Yao, Youguo Shi, and Huaizhou Zhao, Improved figure of merit (z) at low temperature for superior thermoelectric cooling in Mg3(Bi,Sb)2, Nat. Commun. 14, 4932 (2023).
  14. Airan Li, Longquan Wang, Jiankang Li, Xinzhi Wu, and Takao Mori, Self-optimized contact in air-robust thermoelectric junction towards long-lasting heat harvesting, Nat. Commun. 16, 1502 (2025).
  15. Liangjun Xie, Li Yin, Guyang Peng, Shaowei Song, Pingjun Ying, Songting Cai, Yuxin Sun, Wenjing Shi, Hao Wu, Nuo Qu, Fengkai Guo, Wei Cai, Haijun Wu, Qian Zhang, Kornelius Nielsch, Zhifeng Ren, Zihang Liu, and Jiehe Sui, Screening strategy for developing thermoelectric interface materials, Science 382, 921 (2023).
  16. Xinzhi Wu, Yangjian Lin, Chengyan Liu, Yupeng Wang, Huan Li, Binghui Ge, and Weishu Liu, A high performance eco-friendly MgAgSb-based thermoelectric power generation device near phase transition temperatures, Energy Environ. Sci. 17, 2879 (2024).
  17. Zihang Liu, Yumei Wang, Jun Mao, Huiyuan Geng, Jing Shuai, Yuanxu Wang, Ran He, Wei Cai, Jiehe Sui, and Zhifeng Ren, Lithium doping to enhance thermoelectric performance of MgAgSb with weak electron-phonon coupling, Adv. Energy Mater. 6, 1502269 (2016).
  18. Jiehe Sui, Jing Shuai, Yucheng Lan, Yuan Liu, Ran He, Dezhi Wang, Qing Jie, and Zhifeng Ren, Effect of Cu concentration on thermoelectric properties of nanostructured p-type MgAg0.97−xCuxSb0.99, Acta Mater. 87, 266 (2015).
  19. Airan Li, Longquan Wang, Jiankang Li, and Takao Mori, Global softening to manipulate sound velocity for reliable high-performance MgAgSb thermoelectrics, Energy Environ. Sci. 17, 8810 (2024).
  20. Pingjun Ying, Xiaohua Liu, Chenguang Fu, Xianqiang Yue, Hanhui Xie, Xinbing Zhao, Wenqing Zhang, and Tiejun Zhu, High performance α-MgAgSb thermoelectric materials for low temperature power generation, Chem. Mater. 27, 909 (2015).
  21. Zihang Liu, Huiyuan Geng, Jun Mao, Jing Shuai, Ran He, Chao Wang, Wei Cai, Jiehe Sui, and Zhifeng Ren, Understanding, and manipulating the intrinsic point defect in α-MgAgSb for higher thermoelectric performance, J. Mater. Chem. A 4, 16834 (2016).
  22. Zhenzhen Feng, Jihua Zhang, Yuli Yan, Guangbiao Zhang, Chao Wang, Chenxiao Peng, Fengzhu Ren, Yuanxu Wang, and Zhenxiang Cheng, Ag−  Mg antisitee defect induced high thermoelectric performance of α-MgAgSb, Sci. Rep. 7, 2572 (2017).
  23. Alex Zevalkink, David M. Smiadak, Jeff L. Blackburn, Andrew J. Ferguson, Michael L. Chabinyc, Olivier Delaire, Jian Wang, Kirill Kovnir, Joshua Martin, Laura T. Schelhas, Taylor D. Sparks, Stephen D. Kang, Maxwell T. Dylla, G. Jeffery Snyder, Brenden R. Oriz, and Eric S. Toberer, A practical field guide to thermoelectrics: Fundamentals, synthesis, and characterization, Appl. Phys. Rev. 5, 021303 (2018).
  24. Dandan Li, Huaizhou Zhao, Shanming Li, Beipei Wei, Jing Shuai, Chenglong Shi, Xuekui Xi, Peijie Sun, Sheng Meng, Lin Gu, Zhifeng Ren, and Xiaolong Chen, Atomic disorders induced by silver, and magnesium ion migrations favor high thermoelectric performance in α-MgAgSb-based materials, Adv. Funct. Mater. 25, 6478 (2015).
  25. M. J. Kirkham, A. M. dos Santos, C. J. Rawn, E. Lara-Curzio, J. W. Sharp, and A. J. Thompson, Ab-initio determination of crystal structures of the thermoelectric material MgAgSb, Phys. Rev. B 85, 144120 (2012).
  26. Hyun Seok Oh, Sang Jun Kim, Khorgolkhuu Odbadakh, Wook Ha Ryu, Kook Noh Yoon, Sai Mu, Fritz Körmann, Yuji Ikeda, Cemal Cem Tasan, Dierk Raabe, Takeshi Egami, and Eun Soo Park, Engineering atomic-level complexity in high-entropy, and complex concentrated alloys, Nat. Commun. 10, 2090 (2019).
  27. See Supplemental Material at http://link.aps.org/supplemental/10.1103/gqjx-6kqr for figures and tables containing supporting characterization, calculation, and experimental results, which includes Figs. S1–S17, and Tables S1–S4, Ref. [22].
  28. Kaiwei Guo, Xiaofan Zhang, Zhen Fan, Yi Wang, Jiawei Yang, Hangtian Zhu, Jing Chen, Qi Zhao, Zhiliang Li, Shufang Wang, Qinghua Zhang, Yuan Yao, Lunhua He, and Huaizhou Zhao, Rational manipulation of Ag vacancies for latiice plainification, and superior thermoelectric performance in α-MgAgSb, Chem. Eng. J. 507, 160515 (2025).
  29. Wusheng Zuo, Hongyi Chen, Ziyi Yu, Yuntian Fu, Xin Ai, Yanxiao Cheng, Meng Jiang, Shun Wan, Zhengqian Fu, Rui Liu, Guofeng Cheng, Rui Xu, Lianjun Wang, Fangfang Xu, Qihao Zhang, Denys Makarov, and Wan Jiang, Atomic-scale interface strengthening unlocks efficient, and durable   Mg-based thermoelectric devices, Nat. Mater. 24, 735 (2025).
  30. Liangjun Xie, Guyang Peng, Yuxin Sun, Zihang Liu, Fushan Li, Yuke Zhu, Jianbo Zhu, Hao Wu, Nuo Qu, Wenjing Shi, Lei Jiao, Fengkai Guo, Wei Cai, Haijun Wu, and Jiehe Sui, Semiconductor-Semimetal composite engineering enabling record-high thermoelectric power density for low-temperature energy harvesting, Adv. Funct. Mater. 34, 2401763 (2024).
  31. Yifang Huang, Jingdan Lei, Heyang Chen, Zhengyang Zhou, Hongliang Dong, Shiqi Ynag, Haotian Gao, TIan-Ran Wei, Kunpeng Zhao, and Xun Shi, Intrinsically high thermoelectric performance in near-room temperature α-MgAgSb materials, Acta Mater. 249, 118847 (2023).
  32. Liangjun Xie, Jiawei Yang, Ziyu Liu, Nuo Qu, Xingyan Dong, Jianbo Zhu, Wenjing Shi, Hao Wu, Guyang Peng, Fengkai Guo, Yang Zhang, Wei Cai, Haijun Wu, Hangtian Zhu, Huaizhou Zhao, Zihang Liu, and Jiehe Sui, Highly efficient thermoelectric cooling performance of ultrafine-grained, and nanoporous materials, Mater. Today 65, 5 (2023).
  33. Huaizhou Zhao, Jiehe Sui, ZhongJia Tang, Yucheng Lan, Qing Jie, Daniel Kraemer, Kenneth McEnaney, Arnold Guloy, Gang Chen, and Zhifeng Ren, High thermoelectric performance of MgAgSb-based materials, Nano Energy 7, 97 (2014).
  34. Pingjun Ying, Lennart Wilkens, Heiko Reith, Nicolas Perez Rodriguez, Xiaochen Hong, Qiongqiong Lu, Christian Hess, Kornelius Nielsch, and Ran He, A robust thermoelectric module based on MgAgSb/Mg3(Sb,Bi)2 with a conversion efficiency of 8.5%, and a maximum cooling of 72 K, Energy Environ. Sci. 15, 2557 (2022).
  35. Daniel. Kraemer, Jiehe. Sui, Kenneth. McEnaney, Huaizhou Zhao, Qing Jie, Zhifeng Ren, and Gang Chen, High thermoelectric conversion efficiency of MgAgSb-based material with hot-pressed contacts, Energy Environ. Sci. 8, 1299 (2015).
  36. Bin Zhu, Xixi Liu, Qi Wang, Yang Qiu, Zhong Shu, Zuteng Guo, Yao Tong, Juan Cui, Meng Gu, and Jiaqing He, Realizing record high performance in n-type Bi2Te3-based thermoelectric materials, Energy Environ. Sci. 13, 2106 (2020).
  37. Bingchao Qin, Dongyang Wang, Xixi Liu, Yongxin Qin, Jin-Feng Dong, Jiangfan Luo, Jing-Wei Li, Wei Liu, Gangjian Tan, Xinfeng Tang, Jing-Feng Li, Jiaqing He, and Li-Dong Zhao, Power generation, and thermoelectric cooling enabled by momentum, and energy multiband alignments, Science 373, 556 (2021).
  38. Zihang Liu, Naoki Sato, Weihong Gao, Kunio Yubuta, Naoyuki Kawamoto, Masanori Mitome, Keiji Kurashima, Yuka Owada, Kazuo Nagase, Chul-Ho Lee, Jangho Yi, Koichi Tsuchiya, and Takao Mori, Demonstration of ultrahigh thermoelectric efficiency of ∼7.3% in Mg3Sb2/MgAgSb module for low-temperature energy harvesting, Joule 5, 1196 (2021).
  39. Tuo Wang, Hong-Yi Chen, Peng-Fei Qiu, Xun Shi, and Li-Dong Chen, Thermoelectric properties of Ag2S superionic conductor with intrinsically low lattice thermal conductivity, Acta Phys. Sin. 68, 090201 (2019).
  40. Tea-Yon Kim, Yujue Wang, Austin L. Raithel, and Thomas W. Hamann, Real-time observation of the diffusion progression from liquid to solid state of transition metal complexes, ACS Energy Lett. 5, 583 (2020).
  41. Jing Shuai, Hee Seok Kim, Yucheng Lan, Shuo Chen, Yuan Liu, Huaizhou Zhao, Jiehe Sui, and Zhifeng Ren, Study on thermoelectric performance by Na doping in nanostructured Mg1−xNaxAg0.97Sb0.99, Nano Energy 11, 640 (2015).
  42. Zihang Liu, Yongsheng Zhang, Jun Mao, Weihong Gao, Yumei Wang, Jing Shuai, Wei Cai, Jiehe Sui, and Zhifeng Ren, The microscopic origin of low thermal conductivity for enhanced thermoelectric performance of Yb doped MgAgSb, Acta Mater. 128, 227 (2017).
  43. Amandine Duparchy, Léo Millerand, Julia Camut, Silvana Tumminello, Hasbuna Kamila, Radhika Deshpande, Aidan Cowley, Eckhard Mueller, and Joohannes de Boor, Establishing synthesis-composition-property relationships for enhanced, and reproducible thermoelectric properties of MgAgSb, J. Mater. Chem. A 10, 21716 (2022).
  44. Joseph Callaway, Model for lattice thermal conductivity at low temperatures, Phys. Rev. 113, 1046 (1959).
  45. Pingjun Ying, Ran He, Jun Mao, Qihao Zhang, Heiko Reith, Jiehe Sui, Zhifeng Ren, Kornelius Nielsch, and Gabi Schierning, Towards tellurium-free thermoelectric modules for power generation from low-grade heat, Nat. Commun. 12, 1121 (2021).
  46. Xiaofan Zhang, Nan Chen, Kaiwei Guo, Qintuo Zhang, Qi Zhao, Jingkun Xu, Hangtian Zhu, and Huaizhou Zhao, High cooling, and power generation performance of α-MgAgSb with intrinsic low lattice thermal conductivity, Mater. Today Phys. 44, 101451 (2024).
  47. Xun Shi and Jian He, Thermopower, and harvesting heat, Science 371, 343 (2021).
  48. Yucheng Lan, Austin Jerome Minnich, Gang Chen, and Zhifeng Ren, Enhancement of thermoelectric figure-of-merit by a bulk nanostructuring approach, Adv. Funct. Mater. 20, 357 (2010).
  49. https:/cstr.cn/31113.02.CSNS.GPPD.
  50. Zhijia Han, Zhigang Gui, Y. B. Zhu, Peng Qin, Bo-Ping Zhang, Wenqing Zhang, Li Huang, and Weishu Liu, The electronic transport channel protection, and tuning in real space to boost the thermoelectric performance of Mg3+δSb2−yBiy near room temperature, Research 2020, 1672051 (2020).
  51. S. S. Li, Scattering mechanisms and carrier mobilities in semiconductors, Semi. Phys. Quant. Electron. Optoelectron. 211 (2006).
  52. Chaoliang Hu, Kaiyang Xia, Chenguang Fu, Xinbing Zhao, and Tiejun Zhu, Carrier grain boundary scattering in thermoelectric materials, Energy Environ. Sci. 15, 1406 (2022).
  53. G. Kresse and J. Furthmüller, Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set, Comput. Mater. Sci. 6, 15 (1996).
  54. John P. Perdew, Kieron Burke, and Matthias Ernzerhof, Generalized gradient approximation made simple, Phys. Rev. Lett. 77, 3865 (1996).
  55. Alex D. Becke and Erin R. Johnson, A simple effective potential for exchange, J. Chem. Phys. 124, 221101 (2006).
  56. Fabien Tran and Peter Blaha, Accurate band gaps of semiconductors, and insulators with a semilocal exchange-correlation potential, Phys. Rev. Lett. 102, 226401 (2009).
  57. Andreas Savin, Reinhard Nesper, Steffen Wengert, and Thomas F. Fässler, Angew. Chem., Int. Ed. Engl. 36, 1808 (1997).
  58. Atsushi Togo, First-principles phonon calculations with phonopy, and phono3py, J. Phys. Soc. Jpn. 92, 012001 (2023).

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Phys. Rev. X 16, 021011– Published 10 April, 2026
  • Received 12 December 2025
  • Revised 10 March 2026
  • Accepted 20 March 2026
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