Study of Defect Sites in Ce1-xMxO2-δ (x=0.2) Solid Solutions Using Raman Spectroscopy

A series of Ce1-xMxO2-delta(M = Gd, Zr, La, Sm, Y, Lu, and Pr) samples were characterized by Raman spectroscopy to investigate the evolution of defect sites (oxygen vacancies and MO8-type complex) and their distributions in the samples. It was found that the evolution of oxygen vacancies was due to the different ionic valence state of dopant from that of Ce4+, while the evolution of the MO8-type complex was due to the different ionic radius of dopant from that of Ce4+. The distributions of defect sites were investigated using 325 and 514 nm excitation laser lines, indicating that the defect sites were surface enriched. Moreover, the increasing ordering level of the sample led to a decline in the concentration of the MO8-type complex in the sample but the constant concentration of oxygen vacancies, implying that the metastable MO8-type complex species were more disordered compared to the oxygen vacancies.