The formation of surface stable anion vacancy states at CeO2 ultra-small crystallite dimensions

► A decrease in lattice parameter with crystallite size occurs for a terbia doped ceria sample. ► The lattice parameter variation is consistent with quantum size or surface tension effects. ► Changes in lattice parameter are not due to changes in anion vacancy concentration. ► Terbia and ceria form a good solid solution over the entire composition range. ► There is no evidence for increased reducibility in these mixed oxides.