1986 Volume 50 Issue 5 Pages 515-520
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.
(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.
(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%.
(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.
(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.
