Defect characterization in Ce0sub(2-x) at elevated temperatures

The atomic defect structure of nonstoichiometric ceria was studied by means of X-ray diffraction. Polycrystalline samples of Ce0sub(2-x) (0 <= x <= 0.21) have been examined at 900 and 10000C, with the stoichiometry controlled by adjusting the oxygen partial pressure between 1 and 10-21 atm. It was observed that the lattice expands as a function of increasing defect concentration and exhibits only fluorite-like diffraction peaks. The integrated intensities of the Bragg reflections were analyzed for Ce02 and Ce0sub(1.91) at 9000C by difference electron-density techniques. It was concluded that the cation sublattice is essentially intact, and the oxygen sublattice must be defective in nonstoichiometric ceria. Least-squares analyses on Ce0sub(2-x)(0 <= x <= 0.21) at 900 and 10000C supported the electron-density results and also showed that the temperature factors of both cations and anions increase with an increase in defect concentration, implying greater mean-square displacement of the atoms from their equilibrium positions. (author)