Crystal Structure and Phase Relationships in the Reduced-Reoxidized Ceria-Zirconia Solid Solution
The crystal structures of reduced-reoxidized ceria-zirconia solid solutions, Ce2Zr2O7+x, with an ordered arrangement of Ce and Zr ions were studied by transmission electron microscopy (TEM), X-ray powder diffraction and thermogravimetric analysis. The oxygen absorption of Ce2Zr2O7 with pyrochlore structure (space group m Fd 3 ) was revealed to proceed through two-step reaction; reaction from Ce2Zr2O7 to b-Ce2Zr2O7.5 around 400K and reaction from b-Ce2Zr2O7.5 to Ce2Zr2O8 about 600K. b-Ce2Zr2O7.5 phase with space group m F 3 4 was thought to be formed by occupation of the half ordered oxygen vacancies with oxygen ions periodically. The oxidation from Ce2Zr2O7 to b-Ce2Zr2O7.5 was also occurred at room temperature by keeping for about 1 year or by irradiation of an electron beam in TEM. On the other hand, the crystal structure of Ce2Zr2O8, completely oxidized state of Ce2Zr2O7, belongs to the space group of m P 3 4 or 23 P from the rule for possible diffractions and the symmetry of the ordering cations.
Z.Y. Zhong, H. Saka, T.H. Kim, E.A. Holm, Y.F. Han and X.S. Xie
T. Sasaki et al., "Crystal Structure and Phase Relationships in the Reduced-Reoxidized Ceria-Zirconia Solid Solution", Materials Science Forum, Vols. 475-479, pp. 1351-1354, 2005