Zirconia–Ceria Solid Solution Synthesis and the Temperature–Time–Transformation Diagram for the 1:1 Composition |
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Authors: | Masatomo Yashima Kenji Morimoto Nobuo Ishizawa Masahiro Yoshimura |
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Affiliation: | Research Laboratory of Engineering Materials, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 227, Japan |
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Abstract: | Zirconia–ceria solid solutions of tetragonal symmetry ( t 'ZrO2) containing 30 to 65 mol% ceria were prepared by annealing c '-ZrO2 at 627°C samples sintered at 1660–1760°C, where c '-ZrO2 is defined as a cubic or tetragonal phase whose axial ratio c/a (tetragonality) is equal to 1. The lattice parameters and the cube root of the unit cell volumes of the annealed samples increased linearly with the ceria content but, on the other hand, the axial ratio c/a (tetragonality) decreased to 1.000 at 70 mol%. During the annealing of each sample, the cell volume decreased because the residual Ce3+ ions were oxidized to the smaller Ce4+. The temperature–time–transformation (TTT) diagram of the 1:1 solid solution was investigated for the c'-t' diffusionless phase transition and the c'–(t + c) diffusional reaction. The c'–t' transformation was found to behave as a thermally activated process with an activation energy estimated to be 113 kJ/mol. This value may indicate that c'–t' transformation is controlled by oxygen diffusion accompanied by dimensional changes of the cerium ions. |
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