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

Abstract

Low thermal conductivity and excellent mechanical strength are essential to pyrochlore A2B2O7 ceramic for environmental/thermal barrier coating applications. To collaboratively tailor the mechanical and thermal properties of A2B2O7 ceramic, a novel high entropy pyrochlore ceramic (La0.3Gd0.3Ca0.4)2(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)2O7 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 (La0.3Gd0.3Ca0.4)2(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)2O7 exhibits enhanced fracture toughness (1.68 MPa m1/2), 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 Al2O3/Al2O3 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 (La0.3Gd0.3Ca0.4)2(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)2O7 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.