EXAFS STUDY OF THE FLUORITE-TYPE COMPOUNDS IN THE SYSTEMS (1-X)ZRO2-XYBO1.5 (X = 0.18-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-0.5) AND ZR2LN2O7 (LN = TB, DY, HO, ER, AND YB)

The local structures of the fluorite-type compounds with a composition of Zr2Ln2O7 (Ln = Gd, Dy, Ho, Er and Yb) have been studied by means of EXAFS spectroscopy. The EXAFS results indicate that Ln3+ ions are essentially 8-coordinated by oxide ions but Zr4+ ions are 6-coordinated. The distinct difference in coordination number between Zr4+ and Ln3+ ions means that the local structures of the fluorite-type Zr2Ln2O7 are similar to the pyrochlore-type structure, even though both Zr4+ and Ln3+ ions are located statistically at the cation sites (4a site) in the fluorite-type lattice. The local structure of the fluorite-type solid solution in the system (1-x)ZrO2-xYbO1.5 (0.18 less-than-or-equal-to x less-than-or-equal-to 0.50) has been also studied by EXAFS spectroscopy. The result indicates that the coordination numbers of Zr4+ and Yb3+ ions are 6 and 8, respectively, in the solid solution in the compositional range 0.18 less-than-or-equal-to x less-than-or-equal-to 0.50, and that the oxygen vacancies are located adjacent to Zr4+ ions.