Effects of rare earth ions (Ln = Er, Y, Sm) on the structure, mechanical and thermal properties of (Ce0.2Zr0.2La0.2Yb0.2Ln0.2)O2-δ high-entropy fluorite oxides: Experiments and first-principles calculation

In this study, (Ce 0.2 Zr 0.2 La 0.2 Yb 0.2 Ln 0.2 )O 2- δ (Ln = Er, Y, Sm; labelled as H-Er, H-Y, H-Sm) high-entropy fluorite oxides (HEFOs) are designed by standard deviation and first-principles calculation. These HEFOs are subsequently synthesized via solid-phase reaction method, and the phase formation, microstructure, mechanical and thermal properties of the three samples have been systematically investigated. The results show that the three samples, exhibiting a single-phase fluorite structure, are successfully prepared after sintering at 1600 °C, and all the elements are uniformly distributed with no elemental segregation and agglomeration. The calculated δ of H-Er, H-Y and H-Sm are 0.3399, 0.3668 and 0.3458, respectively, so the chemical formula of three HEFOs are (Ce 0.2 Zr 0.2 La 0.2 Yb 0.2 Er 0.2 )O 1.6601 , (Ce 0.2 Zr 0.2 La 0.2 Yb 0.2 Y 0.2 )O 1.6332 and (Ce 0.2 Zr 0.2 La 0.2 Yb 0.2 Sm 0.2 )O 1.6542 , respectively. Additionally, the effects of rare earth ions (Er, Y and Sm) on the hardness, Young's modulus and thermal conductivity of HEFOs are analyzed. H-Y exhibits the highest hardness value and largest Young's modulus among the three HEFOs, primarily due to the largest mean acoustic velocity and cohesion energy in absolute value, smallest AGS and average bond lengths. The thermal conductivities ( κ ) of the three samples are only 1.465–1.598 W m −1  K −1 at 1000 °C. Furthermore, the thermal conductivities of the three samples are significantly lower than that of 8YSZ within the temperature range from 25 °C to 1000 °C, and H-Sm exhibits the lowest thermal conductivity in this temperature range. Consequently, they are anticipated to have promising applications in the field of thermal barrier coatings (TBCs).