Study of Oxygen Vacancies in Ce_0.9Pr_0.1O₂_-_δ Solid Solution by in Situ X-ray Diffraction and in Situ Raman Spectroscopy

Abstract

A Ce0.9Pr0.1O2-δ solid solution was prepared by a sol−gel method. Changes in microstructure of the solid solution under different atmospheres (O2, He, and H2) and temperatures were characterized by an in situ X-ray diffraction (XRD) technique. Raman peaks at 460 cm-1 ascribed to the F2g vibration mode of CeO2 in the fluorite structure and at 570 cm-1 ascribed to oxygen vacancies in the solid solution were studied by in situ Raman spectroscopy using 785- and 514-nm excitation laser lines, providing bulk and surface information, respectively. With a 785-nm laser line, the A570/A460 ratio reflecting the oxygen vacancies concentration increased under O2 and He while it first increased and then decreased under H2 with increasing temperature. With a 514-nm excitation laser line, the A570/A460 ratio decreased with increasing temperature under all atmospheres. The growth of the A570/A460 ratio under the 785-nm laser line was due to the positive effects of high temperature and high concentration of oxygen vacancies and the negative effect of reduction of the sample under reducing atmospheres (He and H2), while the decline in the A570/A460 ratio under 514 nm was due to the dominant negative effect of the migration of surface Pr from surface to bulk during the heating process.