LOCAL STRUCTURES AROUND Y ATOMS IN Y//2O//3-STABILIZED TETRAGONAL ZrO//2.

Local structures around Y**3** plus ions in stabilized tetragonal ZrO//2 with the chemical compositions of 94 ZrO//2 multiplied by (times) 6 YO//1//. //5(Y 6) and 86 ZrO//2 multiplied by (times) 4 YO//1//5 multiplied by (times) 10 CeO//2(Y4) were studied by Y K EXAFS (extended X-ray absorption fine structure) analysis. Using Y//2O//3 crystals (Y-O equals 2. 28 Angstrom, six-fold coordination) as a reference sample, average Y-O distances for Y 6 and Y 4 samples were estimated to be 2. 31 and 2. 35 Angstrom by the curve-fitting method, respectively. Y atoms in the tetragonal zirconias seem to locate at seven-fold coordination sites, judging from the atomic distances. The average Y-cation distances for Y 6 and Y 4 samples were calculated to be 3. 70 and 3. 73 Angstrom, respectively. They are longer than the average cation-cation distances calculated from the lattice dimensions, but shorter than the average Y-Y distance of 3. 77 Angstrom in the Y//2O//3 crystals. A Zr//2Y//2O//7 cluster was proposed as a model for local structures around Y**3** plus ions.