Relationship between nano scale defect structure and composition of cerium oxide solid solutions

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Research on cerium oxide solid solution, especially on (1)fabrication of thin films, (2)nano scale defect structure of the solid solution, and (3)the effect of annealing time on the structure was performed. (1)Several methods were tested to fabricate cerium oxide thin films. Homogeneous precipitation method was useful if very thin film of cerium oxide was needed. For thicker films of cerium oxide, the hydrothermal technique was better. (2)As-sintered cerium oxide solid solution was investigated by x-ray diffraction and Raman spectroscopy. In all three different dopants (NdO_<1.5>,GdO_<1.5>, and YO_<1.5>), x-ray diffraction indicated that at the concentration of about 0-40 mol % of these dopants, the solid solution was in fluorite structure. At higher concentrations, many satellite peaks were present but it was very difficult to distinguish between fluorite structure with satellite peaks and rare earth C-type structure. The Raman spectroscopy revealed that the system of NdO_<1.5>-CeO_2 … More maintained the basic fluorite structure even at higher concentration of NdO_<1.5>. For the system of GdO_<1.5>-CeO_2, the Raman band due to interaction between Ce and O remained the same as the fluorite structure at 0-30 mol % GdO_<1.5>, but the Raman band changed to a new position and stayed there up to 70 mol % GdO_<1.5>. For the system of YO_<1.5>-CeO_2, the Raman band due to the interaction between Ce and O changed continuously as the concentration of YO_<1.5> increased from 30 to 70 mol %, indicating continuous structural change in this system. (3)The effect of annealing on the crystal structure of these cerium oxide solid solutions was investigated. The annealing was performed at 900℃ and 1400℃ for the maximum period of 336 days. The samples of the system of YO_<1.5>-CeO_2 showed the change in lattice parameter during the annealing. This was due to the crystal structure change from fluorite structure to rare earth C-type structure with different lattice parameters. On the other hand the specimens of the systems of NdO_<1.5>-CeO_2 and GdO_<1.5>-CeO_2 were found to be very stable during the annealing. Less