Oxygen Absorption Behavior of Ce2Zr2O7+x and Formation of Ce2Zr2O7.5

巌, 佐々木; 良雄, 右京; 明彦, 須田; 正洽, 杉浦; 光太郎, 黒田; 重勇, 荒井; 公恭, 坂

doi:10.2109/jcersj.111.382

Cited by 50 publications

(71 citation statements)

References 21 publications

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“…On the other hand, the present EELS measurements showed that the valence of the zirconium ion remained unchanged, while the valence of the cerium ion successively changed from 3 to 3.5 and 4, with increasing the oxygen content (by filling the oxygen vacancies near the zirconium ions) in the transformations from Ce 8) These features can be again explained qualitatively in terms of the Pauling's rule: with increasing the oxygen content, the coordination number (the number of oxygen ions) of zirconium ions increases, while the total charge neutrality is compensated by the valence change of cerium ions. It is considered that the cation-anion radius ratio of zirconium is still smaller than the critical value required for stabilizing the coordination polyhedra in the Ce milestone for understanding why the ceria-zirconia solid solution exhibits the excellent oxygen absorption/release properties.…”

Section: Elnes Of Cerium-mmentioning

confidence: 51%

Valence Change of Cations in Ceria-Zirconia Solid Solution Associated with Redox Reactions Studied with Electron Energy-Loss Spectroscopy

et al. 2004

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It has been known that the ceria-zirconia solid solutions (Ce 2 Zr 2 O 7þx , 0 5 x 5 1) have an excellent ability for oxygen absorption/release. The local charge states of cations in the CeO 2 -ZrO 2 solid solutions have been studied by means of electron energy-loss spectroscopy (EELS) attached to a transmission electron microscope. The relative intensity of cerium-M 4;5 white-line peaks from Ce 2 Zr 2 O 7 , Ce 2 Zr 2 O 7:5 and Ce 2 Zr 2 O 8 showed a systematic change, which corresponded to the valence change of cerium; Ce 3þ in Ce 2 Zr 2 O 7 , Ce 4þ in Ce 2 Zr 2 O 8 . By contrast, the valence of the zirconium ions, which are mainly at the nearest neighbor sites of absorbed or emitted oxygen atoms, remains to be quaternary irrespective of oxygen contents. It was found that the energy-loss near edge structure (ELNES) of the cerium-M 4;5 edge in Ce 2 Zr 2 O 7:5 was well reproduced by the sum of the ELNES profiles of Ce 2 Zr 2 O 7 and Ce 2 Zr 2 O 8 with an equal weight, the phenomenon of which is known as the 'valence fluctuation,' or 'mixed valence state,' often observed in rare earth metal compounds.

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Section: Elnes Of Cerium-mmentioning

confidence: 51%

Valence Change of Cations in Ceria-Zirconia Solid Solution Associated with Redox Reactions Studied with Electron Energy-Loss Spectroscopy

et al. 2004

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“…10) 3. Results and discussion 3.1 Refinement of crystal structure of Ce 2 Zr 2 O 7 The XRD pattern of the Ce 2 Zr 2 O 7 specimen was consistent with the single phase of pyrochloretype structure (space group Fd 3m). The ideal pyrochloretype structure is described as an ordered cubic closepacked array of cations(16c and 16d sites) with the oxygen ions occupying seveneighths of the tetrahedral sites(48f and 8a sites) between the cations.…”

Section: )mentioning

confidence: 72%

“…The pattern exhibits the 200 and 600 reflections, forbidden for the space group Fd 3m of the pyrochlore structure. According to our previous paper, 7) the space group of the bCe 2 Zr 2 O 7.5 phase was determined to be F 43m, which corresponds to the minimal supergroup of Fd 3m. The most probable structure of bCe 2 Zr 2 O 7.5 may thus be constructed by filling every second position of the 8b site (oxygen vacancy site) of Ce 2 Zr 2 O 7 with oxygen.…”

Section: )mentioning

confidence: 99%

Crystal Structure of Ce2Zr2O7 and .BETA.-Ce2Zr2O7.5

Sasaki

Ukyo

Kuroda

et al. 2004

J. Ceram. Soc. Japan

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The crystal structures of Ce 2 Zr 2 O 7 and bCe 2 Zr 2 O 7.5 were precisely determined by the Rietveld refinement of powder Xray diffraction data. The present refinement revealed that the structure of bCe 2 Zr 2 O 7.5 was formed by filling a half of oxygen vacancies of Ce 2 Zr 2 O 7 in the specific ordered manner. The oxygen vacancy site is divided into two equivalent sites, one of which is completely occupied, when the composition becomes Ce 2 Zr 2 O 7.5 . The formation of bCe 2 Zr 2 O 7.5 can be well explained on the basis of the argument that Zr 4{ ions tend to be 7fold coordination at low temperatures. The derived local atomic displacements associated with the oxygen absorption/release, particularly those of oxygen at the specific sites, could be a key issue to solve the reason why Ce 2 Zr 2 O 7{x exhibits the excellent property of oxygen release and absorption even at relatively lower tempera tures.

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“…However, if the sample is then oxidised under mild conditions, low temperature reduction results, usually in the form of a two peak profile, with the high temperature peak coinciding with the high temperature peak observed after the severe oxidation treatment. Recent literature reports have provided evidence that a particular structure of Ce 2 Zr 2 O 8 , the j-phase, shows low temperature reduction [6][7][8][9][10][11][12]. The j-phase contains pyrochlore-type cation ordering and it is in fact produced by low temperature oxidation of the corresponding pyrochlore structure.…”

Section: Introductionmentioning

confidence: 99%

Structural investigation of Ce2Zr2O8 after redox treatments which lead to low temperature reduction

et al. 2006

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Structural investigations of various aliquots of Ce2Zr2O8 were conducted after application of well-defined redox treatments. The results indicate that specific redox procedures induce modifications in the ceria-zirconia mixed oxide, which lead to notable effects on the hydrogen uptake temperature during Temperature Programmed Reduction (TPR). Pyrochlore-type cation ordering is evident for an aliquot which exhibits a single low temperature peak during TPR. However, the cation ordering is not complete in this case. Furthermore, the analysis indicates less extensive pyrochlore-type cation ordering for an aliquot which shows a TPR profile in which there are two peaks, one at high temperature and one at low temperature. Finally, an aliquot that exhibits a single high temperature TPR peak shows no evidence of cation ordering. The trend in the promotion of reduction to low temperature is associated with the extent of the pyrochlore-type cation ordering

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Oxygen Absorption Behavior of Ce2Zr2O7+x and Formation of Ce2Zr2O7.5

Cited by 50 publications

References 21 publications

Valence Change of Cations in Ceria-Zirconia Solid Solution Associated with Redox Reactions Studied with Electron Energy-Loss Spectroscopy

Valence Change of Cations in Ceria-Zirconia Solid Solution Associated with Redox Reactions Studied with Electron Energy-Loss Spectroscopy

Crystal Structure of Ce2Zr2O7 and .BETA.-Ce2Zr2O7.5

Structural investigation of Ce2Zr2O8 after redox treatments which lead to low temperature reduction

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