Effects of Thermal Annealing and X-ray Exposure on Local Structures Surrounding Co in (Y. Co)-codoped CeO2 Nanocrystals
T. S. Wu1*, S. L. Chang1,2, H. T. Jeng1, Y. L. Soo1,2
1Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
2National Synchrotron Radiation Research Center, Hsinchu, Taiwan
* presenting author:吳泰興, email:wts4832@gmail.com
Codoping of Y and Co in CeO2 has been found to incur an unconventional bandgap narrowing effect in the host nanocrystal material. The dormant bandgap-tuning ability of Y appears to be turned on by the Co codopant in the oxygen-vacancy-rich CeO2 host. The physical mechanism underlying such effect has also been revealed by DFT calculations. Synchrotron-Radiation-based X-ray absorption analysis has further demonstrated that the Co codopant atoms can be located in either of two different local bonding environments in the CeO2 host. Thermal annealing is capable of driving Co atoms from one bonding environment to the other. On the other hand, when exposed to x-rays of sufficient photon energy, Co can resume the original local structure as in the as-made sample. A simple model is proposed to explain such intriguing interplay between the effects of annealing and x-ray exposure in these codoped nanoceria systems.

Keywords: CeO2, X-ray Exposure, Bandgap-tuning