Preparation and characterization of a novel monazite-type high-entropy (La1/7Ce1/7Pr1/7Nd1/7Sm1/7Eu1/7Gd1/7)PO4 for thermal/environmental barrier coatings

A novel monazite-type high entropy (La1/7Ce1/7Pr1/7Nd1/7Sm1/7Eu1/7Gd1/7)PO4 (HE (7RE1/7)PO4) designed for the thermal/environmental barrier coatings (T/EBCs) material of Al2O3f/Al2O3 ceramic matrix composites (CMCs) has been firstly prepared and comprehensively characterized in this work. HE (7RE1/7)PO4 with a homogeneous rare-earth element distribution exhibits good high-temperature stability up to 1750 degrees C and good chemical compatibility with Al2O3 up to 1600 degrees C in air. The thermal expansion coefficient (TEC) of HE (7RE1/7)PO4 (9.48 x10-6/degrees C) is close to that of Al2O3f/Al2O3 CMCs (9.0 x10-6/degrees C) at room temperature to 900 degrees C. Moreover, HE strategy effectively reduces the thermal conductivity of HE (7RE1/7)PO4 (2.42 W center dot m-1 center dot K-1 to 1.14 W center dot m-1 center dot K-1 from room temperature to 1000 degrees C) in comparison with those of single-component REPO4 with the average values of 3.15 W center dot m-1 center dot K-1 and 1.56 W center dot m-1 center dot K-1. These good compre-hensive properties allow HE (7RE1/7)PO4 to become a promising T/EBCs material for Al2O3f/Al2O3 CMCs in the future.(c) 2023 Elsevier B.V. All rights reserved.