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

In this paper, we report the structural and compostional variation of Ce 2 Zr 2 O 7 pyrochlore under a controlled oxidation/reduction process. On oxidation Ce 2 Zr 2 O 7 transforms to Ce 2 Zr 2 O 8 via an intermediate lattice at Ce 2 Zr 2 O 7.5 . Crystal structures of the Ce 2 Zr 2 O 7, Ce 2 Zr 2 O 7.5, and Ce 2 Zr 2 O 8 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 Ce 2 Zr 2 O 8 composition. The unit cell parameters systematically decreased from Ce 2 Zr 2 O 7 (10.6924(3) Å) to Ce 2 Zr 2 O 8 (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 AO 8 polyhedra similar to that in the fluorite lattice. The transformation from Ce 2 Zr 2 O 7 to Ce 2 Zr 2 O 8 systematically lowers the symmetry from Fd 3 m to P 2 1 3. A complete oxidation of Ce 3+ to Ce 4+ 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 Ce 2 O 3 /CeO 2 −ZrO 2 will have immense importance in the development and understanding of new oxygen storage capacitors.