Abstract
The role of trivalent rare-earth dopants on the cerium oxidation state has been systematically studied by in situ photoemission spectroscopy with synchrotron radiation for 10 mol % rare-earth doped epitaxial ceria films. It was found that dopant rare-earths with smaller ionic radius foster the formation of Ce3+ by releasing the stress strength induced by the cation substitution. With a decrease of the dopant ionic radius from La3+ to Yb3+, the out-of-plane axis parameter of the crystal lattice decreases without introducing macroscopic defects. The high crystal quality of our films allowed us to comparatively study both the ionic conductivity and surface reactivity ruling out the influence of structural defects. The measured increase in the activation energy of films and their enhanced surface reactivity can be explained in terms of the dopant ionic radius effects on the Ce4+ → Ce3+ reduction as a result of lattice relaxation. Such findings open new perspectives in designing ceria-based materials with tailored properties by choosing suitable cation substitution.
| Original language | English |
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| Pages (from-to) | 8841-8849 |
| Number of pages | 9 |
| Journal | Journal of Physical Chemistry C |
| Volume | 121 |
| Issue number | 16 |
| DOIs | |
| State | Published - Apr 27 2017 |
Funding
We thank Regina Ciancio for EDS measurements and useful discussions on composition analysis. N.Y. is thankful for financial support from ShanghaiTech University. The research at ORNL (ESM measurements) was conducted at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Division of Scientific User Facilities, U.S. Department of Energy, supported by Project CNMS2015-028. This work has been partly performed in the framework of the Nanoscience Foundry and Fine Analysis (NFFA-MIUR Italy Progetti Internazionali) facility in Trieste, Italy.