Effect of calcination temperature on cation arrangement and oxygen storage/release capacity in cation-ordered Ce oxides

Cation-ordered κ-Ce2Zr2O8 exhibits a high oxygen storage/release capacity (OSC); however, the cation-ordered phase transforms into a cation-disordered phase during high-temperature calcination, thereby decreasing the OSC. Ti substitution in Ce0.5Zr0.4Ti0.1O2 facilitates the formation of a cation-ordered structure compared to the conventional κ-Ce2Zr2O8, which requires a high-temperature reduction treatment to obtain an ordered structure. In this study, the thermal stabilities of Ce0.5Zr0.4Ti0.1O2 and κ-Ce2Zr2O8 are compared. Powder X-ray diffraction reveals that the onset temperature for the cation disordering of Ce0.5Zr0.4Ti0.1O2 (700 ​°C) is lower than that of κ-Ce2Zr2O8 (1000 ​°C). Furthermore, scanning transmission electron microscopy suggests that the cation disordering of Ce0.5Zr0.4Ti0.1O2 is induced by the high mobility of Ti within the crystal lattice; thus, the OSC decreases and κ-Ce2Zr2O8 exhibits a higher thermal stability than Ce0.5Zr0.4Ti0.1O2. Hence, Ti substitution facilitates the formation of a cation-ordered structure; however, it stimulates cation disordering that lowers the OSC and reduces thermal stability.