Design of oxygen-storage/release materials with high-speed of oxygen-release in rare-earth trivalent cation M³⁺-doped ceria-zirconia system

Abstract

The good correlation between the speed of oxygen-release versus the oxygen-ion conductivity was found in ceria-zirconia under 33 mol % of Ce content. The crystal lattice expansion was also found to affect the speed of oxygen-release in ceria-zirconia with Ce content of 33–66 mol %. Because these properties can be controlled by rare-earth trivalent cation M³⁺-doping in ceria-zirconia, the state of M³⁺ and vacancies formed by substituting with M³⁺ has been investigated in typical model samples of M³⁺-doped ceria-zirconia using X-ray powder diffraction and X-ray absorption fine structure. It was experimentally clear that the lattice constant increased with increasing the ionic radius of M³⁺-doped in (Ce_0.5Zr_0.4M_0.1)O_1.95. It was also found that M³⁺ with higher ligand-field stabilization energy of f-orbitals tended to be fully octahedral-coordinated by eight oxygen ions and form free oxygen vacancies un-associated with M³⁺, possibly leading to the high speed of oxygen-release.