A novel approach for the composition design of high-entropy fluorite oxides with low thermal conductivity

High-entropy fluorite oxides (HEFOs) show significant potential for thermal protection applications due to their advantageous combination of low thermal conductivity and high Yong’s modulus. However, the factors influencing its formation have not been well studied and the systematic method for compositional design has not yet been established. In this paper, effects of oxygen vacancy concentration (O_vac) and mean cation radius ( ) on the formability of HEFOs have been investigated aiming to develop a compositional design approach. The results indicate that an appropriate  and O_vac are crucial for promoting the formability of single-phase (Ca_xCe_y1Zr_y2Hf_zSn_zTi_z)O_2-δ HEFOs. High mass/size disorder and appropriate O_vac (10%) result in (Ca_0.2Ce_0.14Zr_0.12Hf_0.18Sn_0.18Ti_0.18)O_2-δ exhibiting the lowest thermal conductivity of 1.24 W·m^-1·K^-1. Building upon these insights and employing a valence combination strategy, three new single-phase HEFOs with low thermal conductivity were successfully designed and synthesized, including (La_0.28Y_0.28Ce_0.18Zr_0.18W_0.08)O_2-δ, (La_0.3Y_0.3Ce_0.2Nb_0.1Ta_0.1)O_2-δ, and (Yb_0.52Ce_0.12Zr_0.12Sn_0.12Nb_0.12)O_2-δ. The design approach will provide a valuable reference for the design of other high-entropy oxides.