Pyrochlore–fluorite dual-phase high-entropy RE 2 (Ce 0.2 Zr 0.2 Hf 0.2 Sn 0.2 Ti 0.2 ) 2 O 7 (RE 2 HE 2 O 7 , RE = La, Nd, Sm, Eu, Gd, Dy) ceramics with glass-like thermal conductivity

In this work, new high-entropy RE 2 (Ce 0.2 Zr 0.2 Hf 0.2 Sn 0.2 Ti 0.2 ) 2 O 7 (RE 2 HE 2 O 7 , RE = La, Nd, Sm, Eu, Gd, Dy) ceramics were successfully prepared. RE 2 HE 2 O 7 ceramics exhibited a pyrochlore–fluorite dual-phase structure. For Sm 2 HE 2 O 7 ceramic, Ce 4+ with larger ionic radius was enriched in the fluorite phase, Sn 4+ and Ti 4+ with smaller ionic radii were enriched in the pyrochlore phase, while Zr 4+ and Hf 4+ with medium ionic radii existed in both phases. Compared with YSZ materials, RE 2 HE 2 O 7 ceramics exhibited a much lower glass-like thermal conductivity (1.19–1.68 W m −1 K −1 , 100–900 °C) and comparable thermal expansion coefficients (8.67–10.85 × 10 −6 K −1 , 1200 °C). Furthermore, due to grain refinement caused by the competition of two phases, the Vickers hardness (10.29–13.85 GPa) of RE 2 HE 2 O 7 ceramics is improved. The results indicate that dual-phase high-entropy RE 2 HE 2 O 7 ceramics are promising candidate materials for the next generation of thermal barrier coatings.