This journal is © the Owner Societies 2014 Phys. Chem. Chem. Phys., 2014, 16, 27065--27073 | 27065 Cite this: Phys. Chem. Chem. Phys., 2014, 16, 27065 Effect of grain size and microstructure on radiation stability of CeO 2 : an extensive study V. Grover,* a R. Shukla, a Renu Kumari, b B. P. Mandal, a P. K. Kulriya, b S. K. Srivastava, c S. Ghosh, d A. K. Tyagi a and D. K. Avasthi b To investigate the variation in the radiation stability of ceria with microstructure under the electronic excitation regime, ceria samples sintered under different conditions were irradiated with high energy 100 MeV Ag ions. The ceria nanopowders were synthesized and sintered at 800 1C (S800), 1000 1C (S1000) and 1300 1C (S1300), respectively. The samples with widely varying grain size, densities and microstructure were obtained. The pristine and irradiated samples were studied by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). None of the samples amorphized up to the highest fluence of 1 Â 10 14 ions per cm 2 employed in this study. XRD and Raman studies showed that the sample with lowest grain size suffered maximum damage while the sample with largest grain size was most stable and showed little change in crystallinity. Raman spectroscopy indicated the enhanced formation of Ce 3+ and related defects in the sample with larger grain size after irradiation. The most intriguing result was the absence of Ce 3+ -related defects in the sample with lowest grain size which actually showed maximum damage upon irradiation. The XPS studies on S800 and S1300 provided concrete evidence for the presence of Ce 3+ and oxygen ion vacancies in S1300. The grain boundaries and grain size dependent stability have been discussed. 1. Introduction Oxide ceramic fuels in the nuclear applications are subjected to various high energy particles. In particular the fuel matrices are under attack by high energy fission products having typical energies in the range 70 to 100 MeV. Most of the oxide based fuels employed in the nuclear technology crystallize in a fluorite-type lattice. More often than not, ceria, CeO 2 , is used as a surrogate material for UO 2 , PuO 2 etc. for studying the material properties of the fuel oxides since ceria possesses an identical structure and has similar thermophysical properties. Furthermore, zirconia and ceria are the possible component of inert matrix fuels such ROX (rock like oxides) 1 or CERMET fuels etc. In view of importance of ceria in nuclear technology, quite a few studies have been performed on CeO 2 wherein the radia- tion stability of ceria has been explored under low energy ions as well as swift heavy ion irradiation. Sonoda et al. 2 performed a study involving CeO 2 irradiated with 210 MeV Xe ions and they could observe the formation of ion tracks wherein the crystal- line lattice structure inside the ion track was maintained. Ishikawa et al. 3 showed detailed structural investigations using XRD thin films irradiated with 150 MeV and 200 MeV 197 Au ions that these ion tracks possess a modified crystalline lattice with larger lattice parameters. It is speculated by Bai et al. 4 that nanocrystalline materials are likely to be more resistant to radiation damage due to annihilation of defect at the grain boundaries (GBs). It has also been shown that swift heavy ions cause annealing of defects in the carbon nanostructure like carbon nanotubes, fullerenes and graphene. 5–8 Recently, several nanocrystalline (NC) materials containing a large fraction of GBs like nickel, 9 copper, 9 gold, 10 palladium, 11 ZrO 2 , 11 and MgGa 2 O 4 (ref. 12) have also been shown to exhibit improved radiation resistance compared with their polycrystalline counterparts. On the other hand it can be argued that the scattering of the electron produced by swift heavy ions (SHI) from the grain boundaries results in confinement of the energy within the grain boundaries, thereby increasing the transient lattice temperature. It is expected that the transient temperature rise will be higher in samples with smaller grain size. 13–15 This is supposed to cause higher radiation damage. It is therefore interesting to study radiation damage on different grain size-samples of CeO 2 . It is well known that the major characteristic of the electro- nic excitation effect under swift heavy ion irradiation is the formation of continuous ion tracks along ion-paths. 16 The formation of these ion-tracks would be critically dependent a Chemistry Division, Bhabha Atomic Research Centre, Mumbai-400085, India. E-mail: vinita@barc.gov.in; Fax: +91-22-25505151; Tel: +91-22-2559 2274 b Inter-University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi-110 067, India c Indian Institute of Technology Kharagpur, Kharagpur-721302, India d Indian Institute of Technology Delhi, New Delhi-110 016, India Received 19th September 2014, Accepted 30th October 2014 DOI: 10.1039/c4cp04215h www.rsc.org/pccp PCCP PAPER Published on 31 October 2014. Downloaded by Indian Institute of Technology Kharagpur on 24/11/2014 03:32:30. View Article Online View Journal | View Issue