Microstructure, mechanical and thermal properties of (Gd1/4Dy1/4Y1/4Er1/4)TaO4 high-entropy ceramics sintered from nanopowder prepared by reverse chemical co-precipitation and freeze drying methods

RETaO 4 ceramic materials exhibit exceptional properties, including reversible second-order ferroelastic phase transformations, high fracture toughness, and low thermal conductivity, making them ideal for use as new multifunctional thermal barrier coatings (TBCs). In this study, nanoscale (Gd 1/4 Dy 1/4 Y 1/4 Er 1/4 )TaO 4 ((4RE 1/4 )TaO 4 ) ceramic powders were synthesized via the chemical coprecipitation method. The effects of processing parameters such as NH 3 ·H 2 O concentration, drying method, and sintering temperature on the morphology and particle size of the (4RE 1/4 )TaO 4 precursor powder were systematically investigated. The (4RE 1/4 )TaO 4 ceramics were prepared by sintering, and their microstructure, mechanical properties, and thermal conductivity were studied. The (4RE 1/4 )TaO 4 ceramics have lower thermal conductivity (∼1.32 W·m -1 ·K -1 at 1000°C) than YSZ ceramics, attributed to the high-entropy effect resulting from the introduction of multiple rare earth elements. Furthermore, (4RE 1/4 )TaO 4 demonstrates superior thermal barrier coatings materials (TBCs), has a higher thermal expansion coefficient (10.3 × 10 -6 K -1 at 1200°C), lower Young’s modulus (78.4 GPa), and enhanced high-temperature phase stability relative to single rare-earth tantalates. The high-entropy design and nanopowder preparation are conducive to improving the performance of high-entropy ceramics and promoting their promotion and application in thermal barrier coatings.