Structural evolution-driven enhancement of thermoelectric performance in Bi-S-Se solid solutions

Bismuth sulfide (Bi₂S₃) is widely recognized for its abundance, non-toxicity, and low cost, making it a material we believe holds great potential for thermoelectric energy conversion. Addressing its inherent low electrical conductivity and the strong coupling between electrical and thermal parameters, we proposed a "structural evolution" strategy. By introducing Selenium (Se) to form a solid solution, we successfully modulated the microstructure from particle-like to lamellar grains, reconstructing the carrier transport channels. This strategy not only significantly enhanced carrier mobility but also effectively reduced lattice thermal conductivity through lattice distortion. Ultimately, we achieved a figure of merit (ZT) of 0.38 at 623 K in, offering a new avenue for developing efficient and eco-friendly thermoelectric materials.

For decades, materials scientists have been searching for efficient thermoelectric materials to convert waste heat directly into electrical energy. While traditional materials like Lead Telluride (PbTe) exhibit excellent performance, the toxic elements they contain have always been a major hurdle for widespread commercial application. Therefore, we turned our attention to Bismuth sulfide(Bi₂S₃)—an alternative that is abundant, environmentally friendly, and low-cost. However, our research highlighted a major bottleneck: the inherently low electrical conductivity of Bi₂S₃. We also realized that traditional doping methods, while capable of increasing carrier concentration, often struggle to simultaneously achieve a high power factor and low thermal conductivity due to the strong interdependence of these parameters.

To break through this limitation, our team (led by Prof. Zhen-Hua Ge from the Faculty of Materials Science and Engineering at Kunming University of Science and Technology) proposed a novel "structural evolution" strategy. Instead of simple impurity doping, we constructed a solid solution system, using the isovalent element Selenium (Se) to substitute Sulfur (S), thereby achieving dual tuning of both the crystal structure and electronic structure.

The team published their work in Journal of Advanced Ceramics on January 4, 2026.

During our experiments, we surprisingly discovered that as the Selenium content increased, the microstructure of the matrix underwent a significant transformation: it evolved from disordered particle-like grains into an ordered lamellar (layered) structure. We believe this physical "structural evolution" is crucial because it effectively reconstructs the carrier transport channels, eliminating the transport barriers associated with Sulfur atoms, which in turn leads to a massive improvement in carrier mobility.

Beyond the microstructural changes, our data revealed that the introduction of Selenium profoundly impacted the electronic band structure. Since Selenium has a lower electronegativity than Sulfur, its weaker electron-binding ability facilitated the excitation of more electrons as free carriers, significantly boosting electrical conductivity. At the same time, the structural evolution played a key role in reducing thermal conductivity. We leveraged the large atomic mass difference between Selenium and Sulfur to induce strong mass fluctuation scattering. Coupled with the grain boundary scattering from the newly formed layered structure, this effectively impeded phonon propagation. Ultimately, we obtained a thermoelectric figure of merit (ZT) of 0.38 at 623 K in the Bi₂SSe₂ sample. Through this study, we challenged the traditional notion of solely pursuing high electrical conductivity or low thermal conductivity. Our experimental data shows that while Bi₂SSe₂ may not be the optimum value in single parameters, it exhibits the best comprehensive performance across the entire temperature range, validating the importance of balanced, synergistic regulation.

Although we have made promising progress, we believe there is still significant room for improvement in Bi-S based materials. Looking forward, we will focus our research on multicomponent co-doping strategies to further decouple electrical and thermal transport parameters. Additionally, we plan to employ nano-interface engineering to introduce multiscale scattering centers, aiming to further suppress lattice thermal conductivity. Furthermore, we will delve into the mechanical reliability and long-term thermal stability of these materials under actual operating conditions, which is a critical step for us to push this material toward mid-temperature power generation application.

This work was supported by the Yunnan Fundamental Research Projects (Grant No. 202401BE070001-004), the Academician (Expert) Workstation of Yunnan Province Program (Grant No. 202405AF140066), the Yunnan Science and Technology Program (Grant No. 202401AT070403), the Outstanding Youth Fund of Yunnan Province (Grant no. 202201AV070005), the National Key R&D Program of China (Grant No. 2022YFF0503804), the National Natural Science Foundation of China (Grant No. 52162029), and the Yunnan Major Scientific and Technological Projects (Grant No. 202302AG050010).

About Author

Zhen-Hua Ge holds a Ph.D. in Materials Science and Engineering from the University of Science and Technology Beijing (2013). He conducted postdoctoral research at the University of South Florida and the Southern University of Science and Technology (SUSTech) before joining the faculty at Kunming University of Science and Technology (KUST) as a high-level talent introduction in 2015. He is currently a Professor and Doctoral Supervisor at the Faculty of Materials Science and Engineering, Kunming University of Science and Technology.

Zhen-Hua Ge’s research focuses on the design and performance regulation of high-efficiency thermoelectric materials, low thermal conductivity materials, and functional coatings. He has extensively studied copper and bismuth-based chalcogenides for waste heat recovery. He has published more than 200 papers in peer-reviewed international journals, including Science, Nature Communications, Advanced Materials, and Joule, with over 8,000 citations and an H-index of approximately 45.

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 (1/33, 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