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

In this work, new high-entropy RE2(Ce0.2Zr0.2Hf0.2Sn0.2Ti0.2)2O7 (RE2HE2O7, RE = La, Nd, Sm, Eu, Gd, Dy) ceramics were successfully prepared. RE2HE2O7 ceramics exhibited a pyrochlore–fluorite dual-phase structure. For Sm2HE2O7 ceramic, Ce4+ with larger ionic radius was enriched in the fluorite phase, Sn4+ and Ti4+ with smaller ionic radii were enriched in the pyrochlore phase, while Zr4+ and Hf4+ with medium ionic radii existed in both phases. Compared with YSZ materials, RE2HE2O7 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 RE2HE2O7 ceramics is improved. The results indicate that dual-phase high-entropy RE2HE2O7 ceramics are promising candidate materials for the next generation of thermal barrier coatings.