Crystal Structural Study of Ho-doped Ceria Using X-ray Powder Diffraction Data

Crystal structural analysis of Ho-doped ceria (Ce0.7Ho0.3O1.85) was performed using both conventional laboratory and synchrotron X-ray diffraction (XRD) data. In the laboratory XRD data, a poor refinement result was achieved based on a cubic phase (space group Fm-3 m, No.225); weighted (R wp) and profile (R p) R-factors were 16.2 and 13.4 %, respectively. However, the R-factors significantly decreased to 8.76 and 6.87 % for the R wp and R p values, respectively, when a secondary cubic phase was added in the refinement model. While the phases were indistinguishable in the laboratory XRD data because of close peak positions, they were clearly separated in the synchrotron XRD data owing to monochromatic wavelength. The final Rietveld refinement results revealed that Ce0.7Ho0.3O1.85 consists of two cubic (Fm-3 m) phases; major Ce-rich phase (Ce:Ho = 78:22, with a lattice parameter of 5.4097(1) A) and minor Ho-rich phase (Ce:Ho = 45:55, with a lattice parameter of 5.3877(1) A). The ratio between the major and minor phases was 66:34. The final converged R wp and R p obtained from the synchrotron XRD data were 12.9 and 10.8 %, respectively.