Local structure and nanoscale homogeneity of CeO2–ZrO2: differences and similarities to parent oxides revealed by luminescence with temporal and spectral resolution

Abstract

Although homogeneity at the atomic level of CeO₂–ZrO₂ with a Ce/Zr atomic ratio close to unity is considered to be one of the main causes for the increased total oxygen storage capacity (OSC), the characterization approaches of homogeneity remain a major challenge. We propose a simple, yet effective method, to assess both structural and compositional homogeneity of CeO₂–ZrO₂ by using Eu³⁺ luminescence measured with time and dual spectral resolution (emission and excitation). For Eu³⁺–CeO₂–ZrO₂ calcined at 750 °C, the X-ray diffraction, Raman and High-Resolution Transmission Electron Microscopy data converge to a single pseudo-cubic phase. However, the evolution of Eu³⁺-delayed luminescence from cubic ceria-like to tetragonal zirconia-like emission reveals the formation of CeO₂- and ZrO₂-rich nanodomains and provides evidence for early phase separation. For Eu³⁺–CeO₂–ZrO₂ calcined at 1000 °C, the emission of Eu³⁺ reveals both structural and compositional inhomogeneity. Our study identifies the differences between the local structure properties of CeO₂ and ZrO₂ parent oxides and CeO₂–ZrO₂ mixed oxide, also confirming the special chemical environment of the oxygen atoms in the mixed oxide as reported earlier by Extended X-ray Absorption Fine Structure investigations.