High-temperature charge-density studies of CeO/sub 2-x/ using X-ray and neutron diffraction techniques

High-resolution Bragg scattering experiments have been used to study the structure of polycrystalline CeO sub 2-x. The in-situ experiments were carried out as a function of temperature (300 less than T less than 1500K). The composition was controlled by flowing gases (CO/CO sub 2 or Ar/O sub 2 mixtures) over the sample. Results of both X-ray and neutron scattering experiments are used to define the principle atomic defects responsible for nonstoichiometry in CeO sub 2-x. Large lattice relaxation effects are observed whose magnitudes increase with increasing defect concentration. Temperature-dependent studies of the stoichiometric state (x = 0), show that lattice anharmonic interactions are important. The symmetry of the lattice anharmonic interactions is the same as the static displacements observed in the nonstoichiometric state. Thus, we propose that lattice anharmonic interactions are the fundamental driving force for the complex strain interactions observed in the nonstoichiometric state.