Ion Implantation Induced Phase Transformation in Fully Stabilized Zirconia

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  • 安定化ジルコニアのイオン注入誘起相変態
  • アンテイカ ジルコニア ノ イオン チュウニュウ ユウキソウ ヘンタイ

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Fully stabilized zirconia with 10 mol% Y2O3 was implanted with 1 MeV nitrogen ions (15N2+) to doses ranging from 1.3×1014 to 4×1016 N/cm2 by using a Van de Graaff accelerator. Changes in the crystal structure of the implanted surface layer were investigated by X-ray diffraction, and the following were obtained.<BR>(1) A new phase transformation from cubic to rhombohedral symmetry was found to occur in the implanted surface layer. The rhombohedral phase (R-phase) is not a stable compound containing nitrogen atoms, but is thought to be a metastable phase induced by the surface stress arising from the radiation damage due to ion implantation.<BR>(2) The lattice parameters of the R-phase are described as a′=0.5179 nm and α′=89.8° (Z=4) for the specimen implanted to a dose of 1×1016 N/cm2. The depth distribution of the implanted nitrogen was approximately a Gaussian profile with the projected range of 500±30 nm and the maximum concentration of 2.6×1020 atoms/cm3. The transformed zone for the specimen was estimated to extend from the surface to a depth of 1 μm, which was about twice as deep as the projected range, and the fraction of the transformed material was estimated to be 74%.<BR>(3) Transmission electron microscopic observation of the implanted surface layer rewealed that no damage in the form of precipitates, large bubbles or voids existed and that the layer was crystalline.<BR>(4) By thermal annealing at temperatures up to 973 K, the R-phase disappeared with little change in the depth profile of the implanted ions. This is attributed not to the diffusion of nitrogen ions but to a reverse transformation from the metastable R-phase to C-phase. The reverse transformation is thought to occur by the thermal relaxation of the stress arising from the radiation damage.

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