Y_2O_3安定化正方晶ZrO_2中のY原子の局所構造

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Local structures around Y^<3 + > ions in stabilized tetragonal ZrO_2 with the chemical compositions of 94 ZrO_2・6YO_<l.5> ( Y 6) and 86 ZrO_2・4YO_<l.5>・10 CeO_2 (Y4) were studied by Y K EXAFS (extended X-ray absorption fine structure) analysis. Using Y_2O_3 crystals (Y-O=2.28Å, 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 2.35Å 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 Å, 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 Å in the Y_2O_3 crystals. AZr_2Y_2O_7 cluster was proposed as a model for local structures around Y^<3 +> ions. The cluster consists of two ZrO_7 and two YO_7 polyhedra which share one oxygen vacancy. If one oxygen vacancy is introduced into the atomic arrangement of tetragonal ZrO_2, four equivalent cation sites change to two bigger and two smaller sites which are respectively positioned along the a axis. A pair of Y^<3 +> ions probably occupies the bigger sites and as a result the c/a axial ratio decreases. Therefore this model is consistent with the fact that the c/a axial ratio decreases with an increase of Y_2O_3 concentration when Y^<3 + >ions are added to tetragonal ZrO_2.
社団法人日本セラミックス協会の論文
1988-03-01

Y_2O_3安定化正方晶ZrO_2中のY原子の局所構造

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