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

Abstract

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) A ˚) to Ce 2 Zr 2 O 8 ( 10.5443(2) A ˚). 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 Fd3m to P2 1 3. A complete oxidation of Ce 3þ to Ce 4þ 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.

New high-pressure phase and equation of state of Ce2Zr2O8

“…The refined unitcell parameters, a ¼ 10.5444(2) Å and V ¼ 1172.37(4) Å 3 , agree with the literature. 29 The structure of Ce 2 Zr 2 O 8 is represented in Fig. 1; its structural parameters are given in Table I.…”

“…In the present study, the color of the sample is bright yellow, which is the typical color of a fully oxidized sample. [27][28][29] The structures of the anion filled pyrochlores are highly similar, and all of them are related to the parent cubic pyrochlore lattice.…”

“…Because cerium oxide (CeO 2 ) is used as a surrogate material to simulate the thermo-physical properties of radioactive PuO 2 , studies on cerium containing oxides are extremely important for nuclear technology. Recently, Surble et al 20 [24][25][26][27][28][29] In particular, Ce 2 Zr 2 O 8 exists as a cubic fluorite structure 29,30 or metastable tetragonal structures. 31,32 It also is well known that the fluorite structure transforms to different crystalline modifications with pressure.…”

Ceria: Recent Results on Dopant-Induced Surface Phenomena

“…In the system Ce-Zr-O different phases such as fluorite-type (Ce,Zr)O 2−δ solid solutions, tetragonally distorted ZrO 2 -rich fluorite structures or pyrochlore Ce 2 Zr 2 O 7 occur depending on Zr/Ce ratio, p O 2 , and temperature [13][14][15][16][17]. Pyrochlore formation is assumed to result in lower redox entropy since possible site occupancies of oxygen vacancies are limited with respect to oxygen vacancy sites in the fluorite structure of pure ceria [17][18][19][20][21].…”

“…Pyrochlore formation is assumed to result in lower redox entropy since possible site occupancies of oxygen vacancies are limited with respect to oxygen vacancy sites in the fluorite structure of pure ceria [17][18][19][20][21]. Although stoichiometry suggests that pyrochlore formation needs a balanced Zr/Ce ratio, Shah et al predict pyrochlore-type clusters in Ce-rich compositions [6].…”