Vibrational spectrum and XPS contrastive studies on pyrochlore-type oxygen-rich Ce2Zr2O8 and oxygen-defective Nd2Zr2O7 phases

Abstract

Pyrochlore-type oxygen-rich Ce2Zr2O8 phase was prepared successfully by graphite reduction method. With the oxygen[U8]-defective Nd2Zr2O7 substituting for the oxidized precursor phase CeZrO3.5+Δ was carried out the structure comparative analysis with Ce2Zr2O8. The X-ray diffraction (XRD), Raman spectroscopy (Raman), infrared spectroscopy (IR) and X-ray photoelectron spectroscopy (XPS) were used to characterize the crystal structure of samples. The XRD experimental results show that Ce2Zr2O8 bulk phase contains the typical structure of pyrochlore, the superstructure peaks that characterize Ce/Zr cations ordering arrangement are very obvious, but the Zr-O ligands had also transformed from octahedrons of the co-top connection in the precursor to cubes of co-edge connection in the Ce2Zr2O8, and the formation of [ZrO8] ligand reduced greatlly the structural stability of Ce2Zr2O8 phase. Raman and IR results show that vibrational spectra bands of Ce2Zr2O8 phase increased significantly, meaning that the enriched oxygen ions result in a removal of the degeneracy peak for Ce2Zr2O8 phase, which confirms further the structural symmetry of Ce2Zr2O8 phase lower than its precursor. XPS results show that Ce (IV) characteristic peak (916.3 eV) in the Ce2Zr2O8 phase surface is very obvious. No the appearance of Ce (III) peak (885 eV) suggests that Ce3+ from the precursor has been completely oxidized into Ce4+ in the Ce2Zr2O8 phase; the Zr(3d) binding energy is close to fluorite phase with Zr4+, which confirms that [ZrO8] ligand in the Ce2Zr2O8 surface is consistent with the bulk phase. The increasing low binding energy of O(1s) shows that oxygen species in the Ce2Zr2O8 bulk phase are between lattice oxygen and adsorbed oxygen, the presence of high oxygen peak suggests that the surface of Ce2Zr2O8 contains adsorbed oxygen, and the bonding strength between adsorption oxygen and Ce2Zr2O8 bulk phase is between CeO2 and Nd2Zr2O7.