Platinum Ion Implantation Into Single Crystal Zirconia With A Carbon Sacrificial Layer on The Surface
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ABSTRACT Single crystal samples of (100) oriented yttria stabilized cubic zirconia are implanted with Pt ions to doses up to 6x10 17 /cm 2 . Our previous studies showed that the retained Pt dose was too small due to the sputter limit. To overcome this problem, a C film was deposited on the surface of some samples before implantation. The implanted samples were annealed isothermally in air at 400'-1200'C, and were analysed with RBS-C and TEM. The C-layer has been found to be very effective for protecting the sample surface from sputtering and thus increasing the Pt concentration by a factor of two, up to 33 mol.% Pt. The as-implanted Pt was nonsubstitutional. After annealing at 1200°C for 1 h, Pt diffused to large depths, and showed a substitutional fraction of about 23%. The detailed TEM measurements on the microstructure and damage of the implanted layer show that after annealing at these temperatures the recovery of ion damage is incomplete. Pt atoms undergo substantial migration concurrently. The Pt at first dissolves in the matrix (though not substitutionally), diffuses and precipitates again at high temperature.
1. INTRODUCTION Surface modification of ceramics by ion beam techniques is already being used to create novel mechanical, optical, chemical, electrical and tribological properties in the surface of alumina, silicon nitride, magnesia and titanium borides and carbides[l]. However, comparatively less work has been reported on the surface modification of zirconias by ion beam methods[2-5]. Yttria-stabilized cubic zirconia is an important oxide ceramic with several applications based upon its unique mechanical properties and its high oxygen ion conductivity. In our previous studies[5], platinum was chosen since it is used in thin film form as a typical electrochemical contact material on zirconia-based electrochemical devices such as oxygen sensors and fuel cells[6]. A dispersed layer of dense precipitates of Pt formed by high dose implantation can be of considerable interest as an alternative conducting layer with large "three phase"(zirconia, Pt and oxygen) volume within the layer. From our previous studies, the retained Pt concentration is small due to the high sputtering rate of zirconia. In this paper, we present our investigation on the possibility of protecting the zirconia surface from sputtering during implantation by coating a sacrificial thin C film on the target surface. Carbon is chosen because it has much smaller sputtering yield than that of zirconia for Pt ion bombardment. 189 Mat. Res. Soc. Symp. Proc. Vol. 354 0 1995 Materials Research Society
2. EXPERIMENTAL
Single crystal samples of (100) oriented cubic zirconia stabilized with 9.5 mol.% yttria were obtained from Ceres Corporation,USA. Carbon was sputter-deposited on the specimens to a thickness of 70 or 210 rnm depending on the Pt dose used. Pt ion implantation was carried out using a metal vapour vacuum arc (MEVVA) high current ion implanter at LBL. Nominal doses of 2 or 6x10 17 /cm 2 were implanted into the specimens with or witho
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