STRUCTURE OF CUBIC YTTRIA DOPED ZIRCONIA BY SYNCHROTRON RADIATION. Y. Matsushima, M. Hayashi, K. Suda, Y. Tabira, N. Ishizawa, Research Laboratory of Engineering Materials, Tokyo Institute of Technology, Nagatsuta, Midori-ku, Yokohama 226, Japan
The structure of yttria-doped zirconia, (Zr1-xYx)O2-x/2 with x=0.242 has been studied by both the synchrotron radiation single-crystal diffraction and EXAFS. The diffraction experiment on a spherical crystal with 35 um in diameter was carried out using a horizontal-type four circle diffractometer at the beam line 14A, KEK-PF. Two wave lengths of 0.7281 Å and 0.75 Å, corresponding to the energies 10 eV and 500 eV below the Y K absorption edge respectively, were employed to enhance the scattering contrast between Y and Zr. The EXAFS spectra of the powdered sample near the Y and Zr K absorption edges were also measured at BL14A employing the transmission mode. The refinements using 83 independent reflections for the 0.75 Å data set and 90 for the 0.7281 Å data set converged with R/Rw factors of 0.0053/0.0051 and of 0.0074/0.0066 respectively. In contrast to the conventional understanding of the fluorite-type structure of this compound, Zr atoms are presumably displaced by about 0.17 Å along <111> from the origin, while Y atoms stay at the origin. In addition, about one third of oxygen atoms are displaced by about 0.35 Å along <001> from the ideal position at 8c site 1/4,1/4,1/4 of the space group Fm3m. The final residual electron density maps indicated that the oxygen atoms near the 8c sites suffer a conspicuous third order enharmonic vibration along <111>, suggesting a possible diffusion path toward the nearest vacant sites of 4b 1/2,1/2,1/2. EXAFS results indicated that Zr-O bond is 2.15(1) Å that is much shorter than the Y-0 of 2.32(1) Å. The coordination number of Zr-O is 8.2 and that of Y-O is 6.2. Combining the results of the EXAFS and the single crystal diffraction, it is suggested that Y and Zr atoms have local structures similar to those found in their parent end-member oxides respectively.