High-entropy (Y0.2Nd0.2Sm0.2Eu0.2Er0.2)AlO3: A promising thermal/environmental barrier material for oxide/oxide composites

Yttrium aluminum perovskite (YAlO 3 ) is a promising candidate material for environmental barrier coatings (EBCs) to protect Al 2 O 3f /Al 2 O 3 ceramic matrix composites (CMCs) from the corrosion of high-temperature water vapor in combustion environments. Nevertheless, the relatively high thermal conductivity is a notable drawback of YAlO 3 for environmental barrier coating application. Herein, in order to make RE AlO 3 more thermal insulating, a novel high-entropy rare-earth aluminate ceramic (Y 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Er 0.2 )AlO 3 was designed and synthesized. The as-prepared (Y 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Er 0.2 )AlO 3 ceramic possesses close thermal expansion coefficient (9.02 × 10 ―6 / o C measured from room temperature to 1200 °C) to that of Al 2 O 3 . The thermal conductivity of (Y 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Er 0.2 ) AlO 3 at room temperature is 4.1 W·m −1  K −1 , which is almost one third of the value of YAlO 3 . Furthermore, to effectively prevent the penetration of water vapor from possible pores/cracks of coating layer, which are often observed in T/EBCs, a tri-layer EBC system RE AlO 3 / RE 3 Al 5 O 12 /(Al 2 O 3f /Al 2 O 3 CMCs) is designed. Close thermal expansion coefficient to Al 2 O 3 and low thermal conductivity of (Y 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Er 0.2 )AlO 3 , as well as the formation of dense garnet layer at (Y 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Er 0.2 )AlO 3 /Al 2 O 3 interface, indicate that this new type of high-entropy ceramic is suitable as a candidate environmental barrier coating material for Al 2 O 3f /Al 2 O 3 CMCs.