High entropy pyrochlore (La0.3Gd0.3Ca0.4)2(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)2O7 ceramic with amorphous-like thermal conductivity for environmental/thermal barrier coating applications

Low thermal conductivity and excellent mechanical strength are essential to pyrochlore A 2 B 2 O 7 ceramic for environmental/thermal barrier coating applications. To collaboratively tailor the mechanical and thermal properties of A 2 B 2 O 7 ceramic, a novel high entropy pyrochlore ceramic (La 0.3 Gd 0.3 Ca 0.4 ) 2 (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 ) 2 O 7 with significant atomic radius and mass fluctuation is proposed by simultaneously introducing various elements with different valence states at A and B cation sites. The as-synthesized (La 0.3 Gd 0.3 Ca 0.4 ) 2 (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 ) 2 O 7 exhibits enhanced fracture toughness (1.68 MPa m 1/2 ), amorphous-like low thermal conductivity (1.45 W m –1 K –1 at 900 °C) and matched thermal expansion coefficient (9.0 × 10 –6 K –1 at 1200 °C) with Al 2 O 3 /Al 2 O 3 CMCs. The extensive misfits in atomic weight, ionic radius among the substitutional cations in combination with the intrinsic oxygen vacancies in the anion sublattice play significant roles in the thermal conductivity reduction of (La 0.3 Gd 0.3 Ca 0.4 ) 2 (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 ) 2 O 7 ceramic. The combination of outstanding mechanical and thermal properties indicates that this type of material has a good application prospect for environmental/thermal barrier coatings.