(La0.5Gd0.5)2(Ce0.2Nb0.2Yb0.2Ta0.2Zr0.2)2O7 high-entropy oxide-based novel thermal barrier coating material

High-entropy oxides (HEOs) are promising materials for thermal barrier coatings (TBCs). In this study, a new type of TBC material, that is, (La 0.5 Gd 0.5 ) 2 (Ce 0.2 Nb 0.2 Yb 0.2 Ta 0.2 Zr 0.2 ) 2 O 7 [(LG)(CNYTZ)O] pyrochlore-structured HEO was designed and synthesized. The results showed that the structure of the (LG)(CNYTZ)O HEO synthesized at 1400 °C for 6 h was pure phase pyrochlore oxide. The microstructures of the (LG)(CNYTZ)O HEO solid specimens were studied after sintering at different temperatures (1500, 1520, 1540, 1550, 1560, 1580, and 1600 °C) for 6 h, respectively. The optimal sintering temperature was determined to be 1550 °C. The properties of the (LG)(CNYTZ)O HEO specimen sintered at 1550 °C for 6 h were tested. Its direct and indirect optical bandgap widths were determined to be 3.05 and 2.52 eV, respectively, from its UV–visible diffuse reflectance spectroscopy profile. Its infrared spectrum was recorded at 1100 °C, which confirmed its excellent high-temperature thermal radiation-shielding properties. Its thermal conductivity was determined in the temperature range of 30–1000 °C after correction for porosity, using the laser flash method, and was found to be in the range of 0.91–1.00 W m −1  K −1 . Its coefficient of thermal expansion ranged from approximately 7.47 × 10 −6 k −1 to 10.36 × 10 −6 k −1 in the temperature of 100–1000 °C. It also exhibited excellent thermophysical properties. Its hardness was in the range of 6.76–7.46 GPa, and its average hardness was measured to be 7.11 GPa using a microhardness tester, while its fracture toughness was in the range of 1.81–2.31 MPa m 1/2 , and its average fracture toughness was 2.06 MPa m 1/2 , respectively. These results indicate that the (LG)(CNYTZ)O HEO can be considered a suitable candidate material for TBCs.