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Author(s) |
Achary, S. N.; Sali, S. K.; Kulkarni, N. K.; Krishna, P. S. R.; Shinde, A. B.; Tyagi, A. K.
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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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