Rare-earth high-entropy magnetoplumbite structure hexaluminates (La1/5Nd1/5Sm1/5Eu1/5Gd1/5)MAl11O19 (M = Mg, Zn) for thermal barrier coating applications with enhanced mechanical and thermal properties

By applying the high-entropy strategy, one can develop stable mixed oxide by populating a single sublattice with many distinct cations. Two kinds of rare-earth high-entropy hexaaluminates (La 1/5 Nd 1/5 Sm 1/5 Eu 1/5 Gd 1/5 )MAl 11 O 19 (M = Mg and Zn) were successfully synthesized, and their mechanical and thermal properties were analyzed. We highlight that the Zn-containing sample displays a significant increase in fracture toughness (2.48 MPa m 1/2 ) and a decrease in thermal conductivity (1500 °C, 1.2 W m −1  K −1 ) as compared to the Mg-containing sample. The diffusion of fine grains in platelet-like grains observed only in the Zn-containing sample is considered to be responsible for its outstanding mechanical properties. This work demonstrates the excellent thermal-mechanical properties of the Zn-containing sample and indicates the promising use of high-entropy hexaaluminate in the aerospace field acting as thermal barrier coating materials.