Nanoscale compositional and structural evolution in ceria zirconia during cyclic redox treatments

摘要

We report changes in nanoscale composition and structure in individual ceria zirconia nanoparticles (nominal composition Ce_(0.7)Zr_(0.3)O2), before and after redox treatment, determined by energy dispersive X-ray (EDX) analysis using scanning transmission electron microscopy (STEM) and high resolution transmission electron microscopy (HRTEM) imaging. According to the chemical analysis of individual nanoparticles, the redox treatments promote the formation of more compositionally homogenous ceria zirconia solid solution nanoparticles, resulting in a uniform low-temperature reduction. Local pyrochlore-type cation ordering in individual nanoparticles was also observed after the high temperature reduction step. For nanoparticles with 70% ceria content, redox cycling treatment was critical to obtain material which exhibits a strong low temperature reducibility. The origin of significant X-ray diffraction line broadening and particle sintering mechanism in the solid solution nanopowders are discussed based on compositional and structural variation within and between individual nanoparticles and oxygen vacancies formed during high temperature reduction treatment.