Pyrochlore-Fluorite Dual-Phase High-Entropy Re2(Ce0.2zr0.2hf0.2sn0.2ti0.2)2o7 (Re2he2o7, Re = La, Nd, Sm, EU, Gd, Dy) Ceramics with Glass-Like Thermal Conductivity

Abstract

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.

Keywords: high-entropy ceramics, dual-phase structure, glass-like thermal conductivity, thermal barrier coatings