Related Experiment Video
Updated: May 20, 2025
Bulk and Thin Film Synthesis of Compositionally Variant Entropy-stabilized Oxides
Published on: May 29, 2018
Insights Into Low-Temperature Cation Ordering in Fe-Added Ce-Zr-Based Oxides
Yume Okazaki1, Akihiro Ishii1, Itaru Oikawa1
1Department of Materials Science, Graduate School of Engineering, Tohoku University, 6-6-02 Aramaki Aoba, Sendai, 980-8579, Japan.
Abstract:
CeO2-ZrO2 (CZ) solid solutions are widely utilized to control the oxygen partial pressure of automobile exhaust purification systems owing to their high oxygen storage capacity (OSC) related to the valence change of Ce ions upon reduction. Among various CZs, cation-ordered κ-Ce2Zr2O8 shows the highest OSC; however, the ordering requires high-temperature reduction above 1200 °C, causing grain growth and potentially compromising the OSC. Recently, it has been reported that adding a small amount of Fe2O3 to CZ (Zr/Ce = 1) lowers the ordering temperature to 800 °C. In this study, Zr-rich CZ, known for its excellent heat resistance and widespread applications, is cation-ordered at low temperatures by the addition of Fe2O3. Using high-temperature in situ XRD, the low-temperature ordering behavior of Fe2O3-added Zr-rich CZ is observed under oxygen partial pressure during reduction. A weakly reducing atmosphere promotes CZ ordering because Fe2O3 remains an ionic Fe that can be dissolved in CZ to facilitate cation migration. In contrast, a strongly reducing atmosphere converts Fe2O3 to metallic Fe, which is unfavorable for CZ ordering. The study suggests that the reduction atmosphere has a significant impact on the dissolution of transition metal oxides and cation ordering of ceramics.
Related Concept Videos
02:54Trends in Lattice Energy: Ion Size and Charge
02:42Ionic Crystal Structures
Most monatomic ions behave as charged spheres, and their attraction for ions of opposite charge is the same in every direction. Consequently, stable structures for ionic compounds result (1) when ions of one charge are surrounded by as many ions as possible of the opposite...
02:58Crystal Field Theory - Octahedral Complexes
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...
02:44The Born-Haber Cycle
03:02Colors and Magnetism
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human...
02:46Crystal Field Theory - Tetrahedral and Square Planar Complexes
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2ây2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2ây2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than...