Synergistic effects of high-entropy engineering and particulate toughening on the properties of rare-earth aluminate-based ceramic composites

Rare-earth aluminates (REAlO₃) are potential thermal barrier coating (TBC) materials, but the relatively high thermal conductivity (k₀, ~13.6 W·m⁻¹·K⁻¹) and low fracture toughness (K_IC, ~1.9 MPa·m^1/2) limit their application. This work proposed a strategy to improve their properties through the synergistic effects of high-entropy engineering and particulate toughening. High-entropy (La_0.2Nd_0.2Sm_0.2Eu_0.2Gd_0.2)AlO₃ (HEAO)-based particulate composites with different contents of high-entropy (La_0.2Nd_0.2Sm_0.2Eu_0.2Gd_0.2)₂Zr₂O₇ (HEZO) were designed and successfully prepared by solid-state sintering. The high-entropy feature of both the matrix and secondary phases causes the strong phonon scattering and the incorporation of the HEZO secondary phase, remarkedly inhibiting the grain growth of the HEAO phase. As a result, HEAO–xHEZO (x = 0, 5%, 10%, 25%, and 50% in volume) ceramic composites show low thermal conductivity and high fracture toughness. Compared to the most commonly applied TBC material—yttria stabilized-zirconia (YSZ), the HEAO–25%HEZO particulate composite has a lower thermal conductivity of 0.96–1.17 W·m⁻¹·K⁻¹ (298–1273 K), enhanced fracture toughness of 3.94±0.35 MPa·m^1/2, and comparable linear coefficient of thermal expansion (CTE) of 10.5×10⁻⁶ K⁻¹. It is believed that the proposed strategy should be revelatory for the design of new coating materials including TBCs and environmental barrier coatings (EBCs).