Phase Relationship and Ni Solubility in Nanoparticles of Ce0.9Zr0.1O2

The phase relationship, defect formation, and incorporation of Ni in Ce0.9Zr0.1O2 have been investigated in samples of nominal composition (Ce0.9Zr0.1)(1-x)NixO2-delta with x=0.03, 0.05 and 0.1, synthesized by a cation complexation route and heat treated at 600, 800 and 1000 degrees C. Several structural (XRD, XAS, HRTEM) and spectroscopic (XPS, Raman) techniques have been used. Our data show the lattice parameters determined from XRD do not significantly vary with the Ni content or annealing temperature. The increasing defect concentration with increasing Ni content revealed by Raman spectra was associated to the formation of oxygen vacancies in the bulk due to coexistence of NiO and Ce0.9Zr0.1O2. On the other hand, no variation in the oxygen vacancies concentration was detected at the surface with increasing the Ni content by XPS data. In those samples with the lowest Ni concentrations (3 and 5 %) and heat treated at 600 degrees C, the analysis of the EXAFS zone of the K-edge of Ni indicates that local order around Ni cations is not long-range, suggesting the presence of a noncrystalline phase. When the Ni content is higher (10 %) and/or the temperature of the thermal treatment is increased, the crystallization of NiO is clearly detected by XRD, EXAFS and HRTEM.