Defect engineering by synchrotron radiation X-rays in CeO2 nanocrystals

This work reports an unconventional defect engineering approach using synchrotron-radiation-based X-rays on ceria nanocrystal catalysts of particle sizes 4.4 – 10.6   nm. The generation of a large number of oxygen-vacancy defects (OVDs), and therefore an effective reduction of cations, has been found in CeO2 catalytic materials bombarded by high-intensity synchrotron X-ray beams of beam size 1.5   mm   ×   0.5   mm, photon energies of 5.5 – 7.8   keV and photon fluxes up to 1.53   ×   1012 photons s − 1. The experimentally observed cation reduction was theoretically explained by a first-principles formation-energy calculation for oxygen vacancy defects. The results clearly indicate that OVD formation is mainly a result of X-ray-excited core holes that give rise to valence holes through electron down conversion in the material. Thermal annealing and subvalent Y-doping were also employed to modulate the efficiency of oxygen escape, providing extra control on the X-ray-induced OVD generating process. Both the core-hole-dominated bond breaking and oxygen escape mechanisms play pivotal roles for efficient OVD formation. This X-ray irradiation approach, as an alternative defect engineering method, can be applied to a wide variety of nanostructured materials for physical-property modification.

Source: Journal of Synchrotron Radiation - August 2, 2018 Category: Physics Authors: Wu, T.-S. Syu, L.-Y. Weng, S.-C. Jeng, H.-T. Chang, S.-L. Soo, Y.-L. Tags: X-ray irradiation defect engineering XANES DFT research papers Source Type: research