Phase stability and thermal properties of dual-phase high-entropy fluorite-pyrochlore oxides

High-entropy fluorite oxides exhibit application potential in thermal barrier coatings. The introduction of pyrochlore phase provides more exploration space for improving thermal properties. However, the phase stability and properties of dual-phase high-entropy oxides (HEOs) need to be further explored. In this paper, high-entropy fluorite single phase and fluorite-pyrochlore dual phase of (ZrHfPrLaSm)O2-delta were synthesized, both of which exhibit excellent high-temperature phase stability at 1600 degrees C. The dual-phase HEOs have lower thermal conductivity and higher thermal expansion than single-phase. The thermal conductivity of dual-phase (Zr0.195Hf0.195Pr0.195La0.195Sm0.22)O2-delta at 1100 degrees C is 1.36W.m(-1).K-1, which is 18.1 % lower than single-phase. The thermal expansion coefficient of dual-phase HEOs is increased to 11.8 x 10(-6) K-1. Compared with single-phase structure, the coexistence of pyrochlore-fluorite structure increases oxygen defect content and lattice distortion degree, resulting in the enhancement of phonon scattering which reduces the thermal conductivity. This study provides guidance for the design and development of high-performance high-entropy ceramics.