Phase evolution and thermophysical properties of high‐entropy RE₂(Y_0.2Yb_0.2Nb_0.2Ta_0.2Ce_0.2)₂O₇ oxides

Abstract

Pursuing novel thermal barrier–coating materials with lower thermal conductivity and high‐temperature stability can simultaneously improve the working efficiency and service temperature of a gas turbine. In this study, a series of high‐entropy RE2(Y0.2Yb0.2Nb0.2Ta0.2Ce0.2)2O7 (RE = La, Nd, Sm, Gd, Dy, and Er) oxides were prepared though solid‐state reaction. Through tuning the rare‐earth cations, an order–disorder transition occurs from certain partially ordered weberite structure (C2221) to disordered defective fluorite structure (Fm3¯$\bar{3}$m). All the high‐entropy RE2(Y0.2Yb0.2Nb0.2Ta0.2Ce0.2)2O7 oxides possess low thermal conductivity in the range of 0.91–1.34 W m−1 K−1 at room temperature, which can be attributed to increased lattice anharmonicity and disorder, resulting in additional phonon scattering. Herein, we proved that the incorporation of heterovalent cations at B‐sites in high‐entropy A2B2O7 crystals is an effective strategy to reduce the thermal conductivity without compromising the decrease of oxygen vacancy. Moreover, the high‐entropy RE2(Y0.2Yb0.2Nb0.2Ta0.2Ce0.2)2O7 oxides show the relatively higher thermal expansion coefficients of 10.3–10.7 × 10−6°C−1 and excellent phase stability at elevated temperatures.

Engineering the mechanical properties of resilient ceramic aerogels

“…57,64 The combination of compositional and microstructure design would result in the development of ceramic aerogels with integrated structural and functional properties. Moreover, the booming of highentropy ceramic [100][101][102][103][104] in recent years could also provide more space for the tuning of chemical compositions, 105 elemental distribution, 106 crystal structures, 107 grain size, 108 and properties 109 in ceramic nanostructures, which offers another perspective for optimization of the mechanical and functional properties of ceramic aerogels.…”