Highly porous (La1/5Nd1/5Sm1/5Gd1/5Yb1/5)2Zr2O7 ceramics with ultra-low thermal conductivity

The high-entropy rare earth zirconate (La 1/5 Nd 1/5 Sm 1/5 Gd 1/5 Yb 1/5 ) 2 Zr 2 O 7 porous ceramics ((5RE 1/5 ) 2 Zr 2 O 7 PCs) were prepared using a foam-gel casting-freeze drying method combined with segmented calcination process. The results of SEM, TEM , and XRD analyses of the (5RE 1/5 ) 2 Zr 2 O 7 PCs indicated the formation of a defective fluorite crystal structure, with the rare earth elements homogeneously distributed. Meanwhile, the as-prepared (5RE 1/5 ) 2 Zr 2 O 7 PCs exhibited high porosity, low bulk density, low thermal conductivity , and relatively high compressive strength . Moreover, the high-temperature thermal conductivity of the samples was evaluated, and the results showed that the (5RE 1/5 ) 2 Zr 2 O 7 PCs maintain a thermal conductivity of 0.150 ± 0.002 W m −1  K −1 even at 1000 °C. The strategy used in this paper can be extended to the synthesis of other high-entropy porous ceramics with high porosity and low thermal conductivity, which is suitable for applications as thermal insulation materials.