Doped ceria materials can be used as solid oxide electrolytes, which form the basis of solid oxide fuel cells, a clean technology with strong potential to support the transition to net-zero carbon. This study solves the long-standing puzzle of why gadolinium (Gd3+) doped ceria has the best performance among the lanthanide doped cerias.
“We found that Gd3+, with its optimal ionic size, helps pave the well-connected pathways in crystal lattice, enabling the smooth diffusion of O2- ions," explains Dr Jing Ming from Queen Mary's, University of London (QMUL), the principal author of this study. “By contrast, the slightly larger Neodymium (Nd³⁺) ion disrupts these pathways and hinders ion transport, resulting in lower ionic conductivity."
The difference in size between the two ionic radii in these materials is just 0.056 Å. Even though the two doped ceria materials share very similar average structures and chemical profiles, the tiny shift in local structure driven by such a tiny dopant size difference could be detected using neutron scattering on the Polaris instrument at ISIS.
Working with ISIS scientists Stephen Hull and Ron Smith, the team from UCL, QMUL, and Warsaw University of Technology combined experimental and theoretical approaches, using isotope-enriched ¹⁶⁰Gd to determine the local structure of Gd-doped ceria using neutron-based techniques for the first time.
Their findings also uncover how dopant size shapes conduction pathways through defect structures, offering valuable insights for the next generation of conducting materials.
Looking ahead, the team aims to explore temperature-dependent behaviour and dynamic processes, combining neutron scattering with complementary techniques and simulations. Their ultimate goal is to build a predictive framework for designing high-performance solid oxide electrolytes, helping to drive forward the development of cleaner and more efficient fuel cells for future energy technologies.
“Neutron scattering are very powerful techniques to uncover the hidden local structural features beyond the average. It made it possible to detect the atomic arrangements inside," says Jing.
Read the full paper here: https://pubs.acs.org/doi/full/10.1021/jacs.5c09862
