Significantly reduced thermal conductivity through dual-site high-entropy strategy in rare-earth hexaaluminates

LaMgAl11O19 (LMA) is an important thermal barrier coating (TBC) material due to its remarkable fracture toughness, excellent sintering resistance and better thermal stability, but the relatively high thermal conductivity limits its application. In this work, single-site high-entropy rare-earth hexaaluminates (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)MgAl11O19 (HE-L), La(Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)Al11O19 (HE-M) and dual-site high-entropy rare-earth hexaaluminates (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)(Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)Al11O19 (HE-LM) ceramics were successfully fabricated by solid-state reaction sintering, and their phase evolution process, mechanical and thermal properties were analyzed. The phase evolution process for the high-entropy rare-earth hexaaluminate is similar to that of the single-component LMA. The dual-site HE-LM ceramic exhibits a significant increase in Vickers hardness (13.63 GPa), fracture toughness (4.18 MPa.m1/2) and a decrease in thermal conductivity (2.02-2.55 W center dot m- 1 center dot K- 1, 25-1100 degrees C) as compared to the LMA ceramics. This work demonstrates the excellent mechanical and thermophysical properties of the HE-LM ceramics. It is expected that the high-entropy rare-earth hexaaluminates will be a promising candidate for TBC.