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Intercalation/Deintercalation of Oxygen: A Sequential Evolution of Phases in Ce2O3/CeO2−ZrO2 Pyrochlores

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posted on 22.12.2009, 00:00 by S. Nagabhusan Achary, Sanjay K. Sali, Narendra K. Kulkarni, P. Siva Ram Krishna, Anil B. Shinde, Avesh K. Tyagi
In this paper, we report the structural and compostional variation of Ce2Zr2O7 pyrochlore under a controlled oxidation/reduction process. On oxidation Ce2Zr2O7 transforms to Ce2Zr2O8 via an intermediate lattice at Ce2Zr2O7.5. Crystal structures of the Ce2Zr2O7, Ce2Zr2O7.5, and Ce2Zr2O8 have been determined accurately from the neutron diffraction data of polycrystalline samples. The retention of cubic pyrochlore-type arrangements is observed even up to the fully oxidized Ce2Zr2O8 composition. The unit cell parameters systematically decreased from Ce2Zr2O7 (10.6924(3) Å) to Ce2Zr2O8 (10.5443(2) Å). All three compositions retain the original pyrochlore-type cation ordering without any intermixing Ce and Zr atoms. All three structures can be explained as cubically coordinated metal atoms, which share the edge of their AO8 polyhedra similar to that in the fluorite lattice. The transformation from Ce2Zr2O7 to Ce2Zr2O8 systematically lowers the symmetry from Fd3m to P213. A complete oxidation of Ce3+ to Ce4+ is observed, in contrast to the kinetically and sterically hindered oxidation proposed earlier. The deep crystallographic insights associated with the oxygen intercalation and deintercalation process in Ce2O3/CeO2−ZrO2 will have immense importance in the development and understanding of new oxygen storage capacitors.

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