Oxygen release behaviour of Ce(1−x)ZrxO2 powders and appearance of Ce(8−4y)Zr4yO(14−δ) solid solution in the ZrO2–CeO2–CeO1.5 system |
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Authors: | Noriya Izu Takahisa Omata Shinya Otsuka-Yao-Matsuo |
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Affiliation: | Department of Materials Science and Processing, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan |
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Abstract: | To clarify the existence of metastable phases in the ZrO2–CeO2–CeO1.5 system, evolved-oxygen gas analyses, (EGA), by heating a single phase of t′ and t″ (Ce(1−x)ZrxO2) with various compositions, x, in a reducing gas and successive oxidation were carried out repeatedly. The oxygen release behaviour of the t′ and t″ phases was very complicated. The single κ phases, (Ce(1−x)ZrxO2) with the composition, x=0.5 and 0.6, which were obtained by oxidizing the resulting pyrochlore as a precursor in O2 gas at 873 K, exhibited a sharp oxygen release at the lowest temperature; the composition range of κ phase may be x=0.450.65. A new tetragonal phase t*, (Ce(1−x)ZrxO2), which was attained by cyclic redox process together with annealing in O2 gas at 1323 or 1423 K, exhibited a sharp oxygen release at the highest temperature; the composition range of t* phase may be as wide as x=0.200.65. A metastable solid solution expressed by a chemical formula of Ce(8−4y)Zr4yO(14−δ) (y=01) possessing a CaF2-related structure appeared on deoxidation of the t* phase. A ternary phase diagram containing the t* and Ce(8−4y)Zr4yO(14−δ) solid solution was proposed. |
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Keywords: | Cerium compounds Powders Oxygen Solid solutions Oxidation Phase transitions Phase diagrams Cerium zirconate Oxygen release |
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