The researchers report TlFe1.6Se2, a layered material in which atomically thin FeSe sheets are periodically embedded inside a bulk host. The concept is to inherit the superior thermoelectric power factor associated with ultrathin FeSe while simultaneously suppressing heat flow in the surrounding crystal.

In their approach, the embedded FeSe layers coexist with ordered iron (Fe) vacancies. These vacancies act as built-in “phonon scatterers.” By disrupting local bonding and creating a complex lattice landscape, the vacancies strongly reduce the mobility of heat-carrying vibrations, lowering lattice thermal conductivity.

Electrical performance improves at the same time. The team finds that Seebeck coefficient values exceed 100 μV K−1 in the Fe-vacancy-ordered phase, delivering a thermoelectric power factor roughly five times larger than in the vacancy-disordered phase. The enhancement is linked to electronic structure changes induced by the vacancy ordering.

A key feature is a reversible temperature-driven transition near 180 °C, where the vacancy arrangement shifts from ordered to disordered. This dynamic behavior further strengthens phonon scattering and pushes thermal conductivity down to about 0.2 W m−1 K−1—at the level of, or lower than, leading thermoelectrics.

The results highlight a “low-dimensional functionality in bulk form” strategy: instead of building devices from films alone, the material embeds the benefits of two-dimensional physics inside a practical bulk crystal. Heavy thallium (Tl) atoms and the complex layered stacking additionally contribute by reducing phonon velocities and increasing scattering.

The publication also suggests broader applicability. Related alkali-intercalated FeSe systems containing potassium, rubidium, or cesium may offer tunable vacancy concentrations, providing a pathway to further optimize thermoelectric performance.

Overall, TlFe1.6Se2 demonstrates that power factor and thermal suppression can be engineered together through structural design—offering a viral, concept-forward blueprint for next-generation waste-heat converters.

Keywords
Thermoelectricity; FeSe; Vacancy ordering; Lattice thermal conductivity; Seebeck coefficient; Power factor; Layered crystals; Phonon scattering

Subject of Research: Not applicable
Article Title: Simultaneous enhancement of power factor and suppression of thermal conductivity in bulk TlFe1.6Se2 via embedded atomically thin FeSe layers
News Publication Date: 30-Apr-2026
Web References: https://pubs.rsc.org/ta/article/14/37/24666/1243050/Simultaneous-enhancement-of-power-factor-and
References: 10.1039/D6TA02075E
Image Credits: Institute of Science Tokyo

The innovation stems from the precise control and manipulation of atomic vacancies—small, intentional gaps where atoms are missing within the crystal lattice. Vacancy engineering allows scientists to dramatically alter and enhance a material’s electrical conductivity and mechanical flexibility by reorganizing these atomic voids. By tuning these microscopic absences, the QUT team has created an alloy that not only harnesses thermoelectric effects with higher efficiency but also exhibits superior ductility, expanding the potential for practical application in flexible and stretchable electronics.

Published in the esteemed journal Nature Communications, this research underscores the synergy between computational materials science and experimental methods. Guided by advanced computational design, the investigators developed a simple yet cost-effective melting synthesis technique, resulting in a flexible AgCu(Te, Se, S) semiconductor with unprecedented mechanical and thermoelectric performance. The dual enhancement of electrical generation from heat and mechanical resilience positions this semiconductor as a rare inorganic candidate with both outstanding conductivity and pliability.

Thermoelectric materials offer the unique advantage of converting thermal energy directly into electrical energy, which is particularly attractive for sustainable energy solutions. The human body itself presents a constant and accessible heat source, creating a natural temperature gradient with the environment that wearable thermoelectric devices can exploit. When a person exercises, the temperature differential further increases, generating more usable thermal energy that can be transformed into power for portable electronics, medical sensors, or communication devices.

Previously, the mainstream materials used for flexible thermoelectrics have been organic compounds or brittle inorganic thin films deposited on flexible substrates, each with inherent limitations. Organic semiconductors generally suffer from suboptimal electrical performance, while inorganic materials, though more efficient, tend to be rigid and prone to cracking under strain. The QUT team’s AgCu(Te, Se, S) semiconductor challenges this dichotomy by maintaining high thermoelectric efficiency alongside exceptional ductility, overcoming a long-standing barrier in the field.

A crucial breakthrough lies in the “vacancy engineering” technique, which the researchers applied to tailor the spatial distribution and concentration of atomic vacancies strategically. These vacancies influence the scattering of electrons and phonons within the crystal, optimizing the balance between electrical conductivity and thermal conductivity—a key metric in thermoelectric materials termed the figure of merit (ZT). By elevating this figure, the material achieves superior heat-to-electricity conversion rates without sacrificing flexibility.

The study highlights that the melting method employed for synthesis is both scalable and economically viable. This simplicity marks a departure from the often elaborate fabrication procedures common in semiconductor development, suggesting promising pathways for commercial manufacture. Moreover, the mechanical robustness endowed by vacancy-engineered microstructures supports repeated bending and stretching, crucial for wearable technology that must endure the dynamic motions of daily life.

This novel semiconductor has already been fashioned into micro-flexible devices designed for direct application on the human arm, effectively demonstrating the practical potential of the technology. These proof-of-concept prototypes illustrate how the material’s ability to conform to complex surfaces and maintain consistent thermoelectric output can revolutionize self-powered health monitoring systems and other wearable electronics, driving forward the vision of ubiquitous, battery-free sensing.

From a physics perspective, the underlying mechanisms of vacancy modulation in multicomponent chalcogenide alloys were largely unexplored until now. The QUT researchers’ elucidation of how vacancy patterns influence both electrical and mechanical properties fills a critical knowledge gap in the field of condensed matter physics and materials chemistry. By contributing foundational insights, this work opens avenues for rational design of other advanced flexible semiconductors with tailored functionalities.

QUT Professor Zhi-Gang Chen, a leading figure in this research, emphasized the rapidly growing demand for flexible thermoelectric devices in an era of wearable technology proliferation. “The key to advancing flexible thermoelectric technology,” he asserts, “lies in exploring a wide array of material systems and innovative fabrication techniques.” This comprehensive approach underpins the team’s success and sets a strategic direction for future advancements in zero-emission power generation.

This advancement aligns with QUT’s broader commitment to carbon neutrality and zero-emission energy solutions, with the project partly supported by the Australian Research Council’s Research Hub in Zero-emission Power Generation for Carbon Neutrality. Parallel efforts at QUT have also yielded ultra-thin, flexible films capable of powering next-generation wearable devices, emphasizing the institution’s position at the forefront of sustainable electronic materials research.

To further explore the full extent of this research and its implications, readers are encouraged to consult the original article titled Strategic vacancy engineering advances record-high ductile AgCu(Te, Se, S) thermoelectrics, available in Nature Communications via DOI: 10.1038/s41467-025-58104-x. The insights from this work promise to catalyze innovations in wearable electronics, flexible energy harvesters, and beyond, heralding a new era of environmentally friendly and mechanically adaptive thermoelectric technologies.

Subject of Research:
Not applicable

Article Title:
Strategic vacancy engineering advances record-high ductile AgCu(Te, Se, S) thermoelectrics

News Publication Date:
21-Mar-2025

Web References:

• Nature Communications Article DOI
• QUT School of Chemistry and Physics
• QUT Centre for Materials Science

References:
Li, N.-H., Shi, X.-L., Liu, S., Cao, T.-Y., Zhang, M., Lyu, W.-Y., Liu, W.-D., Qi, D., & Chen, Z.-G. (2025). Strategic vacancy engineering advances record-high ductile AgCu(Te, Se, S) thermoelectrics. Nature Communications. https://doi.org/10.1038/s41467-025-58104-x

Image Credits:
QUT

Keywords

Thermoelectric materials, Environmental methods, Organic semiconductors, Thermoelectricity, Inorganic chemistry