An anion-deficient high-entropy fluorite oxide with very low density

In this paper, we explored the possibility of forming single-phase high-entropy fluorite oxides (HEFOs) in the (Ce_0.2Zr_0.2Ti_0.2Sn_0.2M_0.2)O_2-δ (M = Mg, Y, Yb, and Ca) system. The result showed that single-phase high-entropy fluorite can only be obtained from (Ce_0.2Zr_0.2Ti_0.2Sn_0.2Ca_0.2)O_2-δ. Compared with other reported anion-deficient HEFOs, this material has the lowest rare earth element content, the smallest average cationic radius and the lowest theoretical density. The effects of cation radius and starting materials on the formation of single-phase HEFOs are discussed.