Inducing and observing reversible phase-transitions in ceria with picometer resolution
Using cutting-edge transmission electron microscopy (TEM) techniques, researchers from RWTH Aachen University, Forschungszentrum Jülich and AMO GmbH have revealed unprecedented details about the reversible phase transition of ceria – a material that holds huge potential for catalytic applications, energy generation, as well as for memristive devices – showing that this can be precisely manipulated with external stimuli, such as electron beams.
Ceria, or cerium oxide (CeO₂), is one of the most promising materials for catalysis, solid electrolytes, and memristor technologies, thanks to its excellent redox properties, oxygen storage capacity, and oxygen ion conductivity. Many of these properties depend on the formation and migration of oxygen vacancies under external stimuli, which are often linked with modifications of the ceria structure and subsequent phase transitions. However, up to now, the atomic-level details of these phase transitions, which are critical to understand and optimize the performance of the material, have remained elusive.
Ke Ran and coworkers at Forschungszentrum Jülich and RWTH Aachen University have tackled these challenges by utilizing a combination of advanced TEM techniques to both induce and visualize phase transitions with sub-Ångstrom resolution. As model system, they focused on gadolinium (Gd)-doped ceria (GDC), a ceria-based oxide used as electrolyte material in solid oxide fuel cells. Their innovative approach allows the simultaneous visualization of both light oxygen atoms and heavy metal atoms, facilitating the measurement of atomic positions with ultrahigh precision. At the same time, the electron beam served also to drive the formation of oxygen vacancies and the phase transition in the material. The observed phase transition appears to be related to a collective rearrangement of oxygen vacancies paired with Ce valence change induced by the electron beam.
“We’ve uncovered that adjusting the electron dose rate during TEM imaging we can control the phase transition of Gd-doped ceria,” explains Ran. “We can accelerate, retard, keep on hold or even reverse the transition, which opens up exciting possibilities for tailoring ceria-based materials to specific needs in energy and electronic applications.”
The findings have far-reaching implications for a wide range of technologies. For instance, in energy applications, it might allow to significantly reduce the temperature needed to trigger ceria’s redox reaction, enhancing the efficiency of ceria-based catalysts and solid electrolytes. In nanoelectronics, this precise control over phase transitions could lead to improved memristors with tunable on/off ratios and greater memory density. “By controlling oxygen vacancy concentrations, we can design materials with highly tailored properties that meet the growing demands for cleaner energy and more advanced electronics,” says Ran.
The results have been reported in Nature Communications.
Bibliographic Information
in situ observation of reversible phase transitions in Gd-doped ceria driven by electron beam irradiation
Ke Ran, Fanlin Zeng, Lei Jin, Stefan Baumann, Wilhelm A. Meulenberg & Joachim Mayer
Nature Communications 15, 8156 (2024)
DOI: https://doi.org/10.1038/s41467-024-52386-3