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Visualizing one-dimensional disorder in a simple inorganic crystal for thermoelectric energy conversion

AU researchers from Department of Chemistry and iNANO have, in collaboration with the University of Tsukuba, found a way to directly monitor the one-dimensional disordered diffusion channel in a simple chain-like thermoelectric InTe. This work provides a new basis for understanding ultralow, weak-temperature-dependent thermal conductivity in simple crystalline solids.

Billede af Professor Bo Brummerstedt Iversen
Professor Bo Brummerstedt Iversen. Foto: AU

A vast range of applications such as space probes, gas pipelines and biomedical devices require self-powered energy harvesting technologies without direct human maintenance. Thermoelectric technology is exactly one such technology, which provides a green, sustainable solution to the energy harvesting for these applications by directly converting heat into electricity in a purely solid-state means. To achieve maximum efficiency, materials used in such technology must minimize thermal conduction. Structural disorder is an efficient strategy of minimizing thermal conduction and is commonly observed in complex crystal structures. However, experimental difficulties hinder researchers' efforts toward probing structural disorder in simple inorganic crystalline solids such as crystals with the thallium selenide-type structure, limiting the development of this important class of thermoelectric materials.

Combining synchrotron single-crystal X-ray diffraction, the maximum entropy method, 3D-ΔPDF, and theoretical calculations, now the AU research team led by Prof. Bo B. Iversen collaborated with the University of Tsukuba have shown the direct visualization of one-dimensional (1D) disordered, diffusive In1+-ion channel in a simple crystalline thermoelectric InTe. The study is published in Nature Communications, where researchers have provided a better understanding of the basis of ultralow thermal conductivity in an intriguing class of simple crystals, which could advance the development of high-performing materials for thermoelectric power technologies.

Indium telluride is a promising thermoelectric material that has a simple crystal structure and exhibits ultralow thermal conductivity. The researchers obtained the electron density distribution of single crystals of indium telluride and probed the thermal conductivity along one axis of the crystal. By doing so, they observed disordered one-dimensional chains of indium ions. Strikingly, with increasing temperature, they found that disordered indium ions become diffusive to form a 1D In1+-ion diffusion/hopping pathway. Theoretical simulations and atomic displacement measurements agree with these observations. The observed atomic disorder provides an important atomic structural origin of ultralow, weak-temperature-dependent thermal conductivity. For the first time, the researchers have provided the direct experimental monitoring of one-dimensional disorder in a simple crystalline solid, thanks to high-energy synchrotron sources and brilliant detectors in the BL02B1 beamline from SPring-8, Japan. The results have experimentally confirmed the chemical and physical basis of an important yet (until now) evasive phenomenon and broadly extended underlying structure-property relationship that is critical to optimizing thermoelectric energy conversion.

"Depending on the temperature, we observed a striking diffusion channel of indium ions along the crystal's c-axis," says Professor Bo B. Iversen, from Department of Chemistry and iNANO at Aarhus University. "Our experiments confirm the long-held one-dimensional diffusion/hopping hypothesis, and our calculations indicate its applicability to many other thallium selenide-type materials."

These results have important applications. Researchers are now certain of the atomic-level structural basis of the low thermal conductivity in thallium selenide-type materials. Accordingly, they can now minimize the trial-and-error that's common in optimizing the efficiency of an important class of upcoming thermoelectric technologies. Such developments will facilitate many practical applications, such as thermal barrier coatings, thermal management in electronics, and waste heat recovery.

Additional information
Method Combination of synchrotron x-ray diffraction, 3D-deltaPDf, maximum entropy method and theoretical calculations
External funding The Villum Foundation, the Danish Agency for Science, Technology and Innovation (DanScatt), and the Aarhus University Center for Integrated Materials Research (iMAT), and partly supported by the Japan Society for the Promotion of Science (JSPS) Grants-in-Aid for Scientific Research (KAKENHI) Grant Number JP19KK0132 and JP20H4656. Theoretical calculations supported by the Center for Scientific Computing in Aarhus (CSCAA)
Link to the scientific article https://www.nature.com/articles/s41467-021-27007-y
Contact information Professor, Dr.Scient. Bo Brummerstedt Iversen, Institut for Kemi, Aarhus Universitet, mail: bo@chem.au.dk