Key Takeaways & Executive Findings
- •• • Achieved peak ZT of 1.35 at 393 K and average ZT of 1.25 over 303–483 K, surpassing many prior BST studies (e.g., Sun et al.: ZT 1.42 at 373 K, avg 1.23; Qu et al.: ZT 1.35 at 393 K, avg 1.25). • • Ag-based compound incorporation raises carrier concentration via Ag+ substitution, enhancing electrical conductivity without degrading Seebeck coefficient. • • Pseudo grain boundary engineering introduces secondary phases that suppress lattice thermal conductivity, reducing total thermal conductivity while preserving carrier mobility. • • The strategy achieves a high average ZT across a broad temperature range (303–483 K), critical for practical device operation where temperature gradients vary.
Abstract
Bismuth telluride (Bi2Te3)-based alloys remain the benchmark for low-temperature thermoelectric applications, yet their conversion efficiency is limited by the trade-off between electrical and thermal transport. This study introduces a pseudo grain boundary engineering strategy to simultaneously enhance the average figure of merit (ZT) in p-type (Bi,Sb)2Te3 (BST) materials. By incorporating Ag-based compounds, the carrier concentration is optimized via substitution of Ag+ ions, while the introduction of secondary phases at grain boundaries effectively suppresses lattice thermal conductivity. The approach yields a peak ZT of 1.35 at 393 K and an average ZT of 1.25 across 303–483 K, representing a significant improvement over pristine BST. Compared to prior reports, this work achieves superior average ZT while maintaining high electrical conductivity, addressing the longstanding bottleneck of thermal conductivity reduction without compromising carrier mobility. The findings underscore the efficacy of pseudo grain boundary engineering in advancing Bi2Te3-based thermoelectrics for solid-state cooling and power generation.
1. Introduction
Bismuth telluride (Bi2Te3)-based alloys are the cornerstone of low-temperature thermoelectric devices, yet their commercial viability is constrained by a relatively low average ZT, which directly limits conversion efficiency. Traditional optimization strategies—such as energy band engineering, grain boundary control, and carrier concentration tuning—have yielded incremental gains, but often at the expense of electrical conductivity or thermal stability. For instance, while porous structures and second-phase additions reduce thermal conductivity, they frequently introduce defects that scatter charge carriers, diminishing the power factor. The challenge lies in decoupling these interdependent transport parameters to achieve a high average ZT over a wide operating temperature range.
This work addresses this bottleneck by employing a pseudo grain boundary engineering approach in p-type (Bi,Sb)2Te3 (BST) alloys. By incorporating Ag-based compounds, the carrier concentration is optimized through Ag+ substitution, while the formation of secondary phases at grain boundaries selectively scatters phonons without significantly impeding electron transport. This dual effect enables a simultaneous enhancement of electrical conductivity and reduction of lattice thermal conductivity, culminating in a peak ZT of 1.35 at 393 K and an average ZT of 1.25 from 303 to 483 K. The results demonstrate a viable pathway to surpass the performance of existing BST materials, offering a practical solution for high-efficiency thermoelectric cooling and power generation.
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Hao Liang, Yilin Liu, Kang Yue, Jianghu Yu, Ziyuan Wang, Tianyu Yang, Yixin Zhang, Jing Feng, Qinglin Jin, Zhenhua Ge (2026). Highly Enhanced Average ZT in Bismuth Telluride Alloys via Pseudo Grain Boundary Engineering. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-026-4381-5
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Frequently Asked Questions
What is the specific role of Ag-based compounds in enhancing the thermoelectric performance of BST?
Ag-based compounds introduce Ag+ ions that substitute into the BST lattice, increasing hole carrier concentration. This optimizes electrical conductivity without significantly altering the Seebeck coefficient. Additionally, the formation of secondary phases at grain boundaries contributes to phonon scattering, reducing lattice thermal conductivity.
How does pseudo grain boundary engineering differ from conventional grain boundary engineering?
Conventional grain boundary engineering often involves introducing secondary phases or reducing grain size, which can inadvertently scatter charge carriers. Pseudo grain boundary engineering, as demonstrated here, selectively forms secondary phases at grain boundaries that primarily scatter phonons, while maintaining high carrier mobility. This results in a more favorable trade-off between electrical and thermal transport.
What are the practical implications of achieving an average ZT of 1.25 over 303–483 K?
An average ZT of 1.25 across a broad temperature range is critical for thermoelectric devices that operate under varying temperature gradients. This performance level enables higher conversion efficiency in real-world applications such as waste heat recovery and solid-state cooling, making the material more commercially viable.
How does the peak ZT of 1.35 at 393 K compare to state-of-the-art BST materials?
The peak ZT of 1.35 at 393 K is competitive with the best-reported values for BST, such as 1.42 at 373 K (Sun et al.) and 1.35 at 393 K (Qu et al.). However, the average ZT of 1.25 over 303–483 K is among the highest reported, indicating superior performance across a wider temperature range.
What are the potential scalability and stability concerns for industrial adoption?
The synthesis process involves standard powder metallurgy techniques, which are scalable. However, the long-term stability of Ag-doped BST under thermal cycling and high-temperature operation needs further investigation. The introduction of secondary phases may affect mechanical robustness, but the current data suggest no significant degradation in performance over the tested temperature range.
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