Thermoelectric technology, which enables the direct conversion of waste heat into electricity, has emerged as a pivotal component in the global pursuit of sustainable energy solutions and carbon neutrality. Among the various candidates for mid-temperature applications (500–800 K), GeTe stands out as a promising lead-free alternative to traditional PbTe materials, owing to its superior electronic band structure and reversible phase transition characteristics. However, the widespread commercial deployment of GeTe is currently hindered by a fundamental physical bottleneck: the severe interdependence between electrical and thermal transport properties. The material’s high intrinsic Ge vacancy concentration results in excessive hole carrier densities, while the strong coupling among the Seebeck coefficient, electrical conductivity, and thermal conductivity makes it notoriously difficult to optimize one parameter without degrading the others.
To overcome this persistent trade-off, a research team led by Prof. Lei Miao from Guangxi University and Prof. Jie Gao from Guilin University of Electronic Technology has developed a novel synergistic doping strategy. Their findings, published in the Journal of Advanced Ceramics on February 4, 2026 , demonstrate how coordinating “shallow impurity level engineering” with “multiscale defect engineering” can decouple these transport parameters, propelling the thermoelectric performance of GeTe to new heights.
The researchers employed a co-doping approach using Sb and Ni. While Sb was primarily used to adjust the carrier concentration to an optimal range, the introduction of Ni played a more complex and critical role in reshaping the material's electronic landscape.
“The core innovation of our work lies in the manipulation of the electronic density of states using Ni,” explained Prof. Lei Miao , the study’s corresponding author. “Unlike conventional dopants such as Zinc or Cadmium, which possess stable full d-shells (d 10 ), Ni has a unique 3d 8 electronic configuration. Our theoretical calculations and experimental results reveal that when Ni substitutes Ge sites, it induces a strong sp-d orbital hybridization near the Fermi level. This interaction not only promotes valence band convergence but, more importantly, introduces shallow impurity levels. These electronic modifications significantly enhance the carrier effective mass (from 1.35 m 0 to 1.96 m 0 ), yielding a high Seebeck coefficient of ~232 μV K -1 at 773 K without severely compromising carrier mobility.”
Beyond the electronic optimization, the team also exploited the chemical reactivity of the dopants to manage heat propagation. The study revealed that a fraction of the Ni dopant reacts in situ with the Ge matrix to precipitate discrete NiGe nanophases. These nanoprecipitates, typically ranging from 10 to 30 nm in size, serve as effective scattering centers for mid-to-high frequency phonons.
“We constructed a robust multiscale defect architecture,” noted Prof. Jie Gao , a co-corresponding author of the study. “By integrating these in situ formed NiGe nanophases with atomic-scale point defects (mass and strain fluctuations) and mesoscale grain boundaries, we achieved full-spectrum phonon scattering. This hierarchical structure effectively suppresses the lattice thermal conductivity to approximately 0.8 W m -1 K -1 at 323 K, which is close to the theoretical amorphous limit of GeTe. Essentially, we created a path for electrons to flow freely while setting up a maze that blocks heat.”
This synergistic approach yields exceptional thermoelectric performance by simultaneously enhancing the power factor through shallow impurity levels and suppressing thermal conductivity via multiscale defects. As a result, the optimized composition Ge 0.885 Sb 0.1 Ni 0.015 Te achieved a peak figure of merit ZT of ~2.15 at 773 K and a high average ZT avg of ~1.45 across the working temperature range of 323 to 773 K. To validate the material's potential for real-world waste heat recovery, the researchers fabricated a single-leg thermoelectric device using Fe electrodes and a SnTe diffusion barrier to ensure stable contact. The device demonstrated a conversion efficiency of approximately 10% under a temperature difference of 420 K.
“This conversion efficiency ranks among the top tier for lead-free GeTe-based devices reported to date,” Prof. Miao added. “Our work not only provides a deep understanding of the role of 3d transition metals in chalcogenides but also establishes a solid foundation for the development of practical, high-efficiency thermoelectric modules.”
About Author
Dr. Lei Miao received a Ph.D. degree from Nagoya Institute of Technology (NITtech.), Japan. She is currently working as the professor in Guangxi University since 2023.06. She was ever appointed as a deputy research leader in Japan Fine Ceramics Centre in 2007, a group leader in Guangzhou Institute of Energy Conversion, CAS from 2008-2015, and a professor in Guilin University of Electronic Technology since 2015.03-2023.05. Her current research focuses on energy conversion materials& devices, especially on thermoelectric and solar thermal applications. Dr. Miao has published over 320 scientific papers, including papers on Nature Comm., Sci Adv., Energy Environ. Sci., Adv. Energy Mater., 6 books, 8 awards. Over 55 authorized Chinese and Japanese patents, over 60 invited speeches in international conferences and etc. The citation times for the main papers have been over 12700 times, H index is 56.
Jie Gao is an associate research follow at Guilin University of Electronic Technology, and his research interests focus on thermoelectric conversion materials and devices, as well as solid-state electrolytes. Prof. Gao has published 15 SCI-indexed papers as the first or corresponding author in journals such as Nature Communications, Journal of Materials Chemistry A, and Journal of Materiomics.
Zhongwei Zhang , PhD candidate at Guangxi University. His research primarily focuses on the design and performance optimization of medium to high temperature thermoelectric materials and devices.
Funding
This work was supported by the National Natural Science Foundation of China (Grant No. U21A2054, 5256130048, 52273285), the Postdoctoral Science Foundation of China (Grant No. 2024MD763940), and the Guangxi Science and Technology Project (Grant No. JF2504850014).
About Journal of Advanced Ceramics
Journal of Advanced Ceramics (JAC) is an international academic journal that presents the state-of-the-art results of theoretical and experimental studies on the processing, structure, and properties of advanced ceramics and ceramic-based composites. JAC is Fully Open Access, monthly published by Tsinghua University Press, and exclusively available via SciOpen . JAC’s 2024 IF is 16.6, ranking in Top 1 (1/34, Q1) among all journals in “Materials Science, Ceramics” category, and its 2024 CiteScore is 25.9 (5/130) in Scopus database. ResearchGate homepage: https://www.researchgate.net/journal/Journal-of-Advanced-Ceramics-2227-8508
Journal of Advanced Ceramics
Synergistic shallow impurity levels and multiscale defect engineering in GeTe-based thermoelectrics
4-Feb-2026