Effect of Annealing on Crystal and Local Structures of Doped Zirconia Using Experimental and Computational Methods

The effects of the annealing process on the crystal and local structures of doped zirconia were investigated by Rietveld refinements of synchrotron X-ray and neutron diffraction, the maximum entropy method (MEM), X-ray absorption spectroscopy (XAS), and first-principles calculations (FPCs). This study reveals that the crystal structures of sintered and annealed (Zr0.85Y0.15)O2-delta (8YSZ) and (Zr0.81Sc0.18Ce0.01)O2-delta (10SSZ) are cubic with the space group Fm (3) over barm and have large atomic displacement parameters (U-iso). The amounts of tetragonal and other phases are less than 0.2 mol % as estimated by comparison of the observed and simulated X-ray diffraction patterns in the annealed zirconia. For annealed 8YSZ, the Uiso values are reduced, and the electrons around the Zr and oxide ion sites gather at the center of each site. On the other hand, annealed 10SSZ shows the opposite tendency as annealed 8YSZ. From the combined XAS and FPC results, the distortion of the ZrO8 polyhedra in zirconia is related to the weakening of the two main peaks of the Zr K-edge, while this distortion increases the strength of the Zr pre-edge. The annealing process is found to enhance the periodic and local distortions of the ZrO8 polyhedra in 10SSZ. In contrast, the annealing process for 8YSZ affects the local distortion of the ZrO8 polyhedra but does not have an effect on the periodic disorder of the crystal structure, as indicated by U-iso values and MEM analyses. We discuss the correlation among the degradation of oxide ion conductivities by the annealing process and the crystal and local structures of the doped zirconia using experimental and computational methods.