High entropy (Y0.2Yb0.2Lu0.2Eu0.2Er0.2)3Al5O12: A novel high temperature stable thermal barrier material

Ytterbium aluminum garnet (Yb 3 Al 5 O 12 ) is considered as a promising thermal barrier material. However, the main limitations of Yb 3 Al 5 O 12 for thermal barrier applications are relative low thermal expansion coefficient and high thermal conductivity . In order to overcome these obstacles, herein, a new high entropy (Y 0.2 Yb 0.2 Lu 0.2 Eu 0.2 Er 0.2 ) 3 Al 5 O 12 ceramic was designed, and then powders and bulk were prepared through solid-state reaction method and spark plasma sintering (SPS), respectively. The thermal expansion coefficient of HE (Y 0.2 Yb 0.2 Lu 0.2 Eu 0.2 Er 0.2 ) 3 Al 5 O 12 is (8.54 ± 0.29) × 10 −6 K -1 at 673 K–1273 K, which is about 9% higher than that of Yb 3 Al 5 O 12 . The thermal conductivity of HE (Y 0.2 Yb 0.2 Lu 0.2 Eu 0.2 Er 0.2 ) 3 Al 5 O 12 ceramic is 3.81 W·m -1 K -1 at 300 K, which is about 18 % lower than that of Yb 3 Al 5 O 12 . Moreover, there is no reaction between HE (Y 0.2 Yb 0.2 Lu 0.2 Eu 0.2 Er 0.2 ) 3 Al 5 O 12 and thermally grown (TG) Al 2 O 3 even at 1600 °C. After annealing at 1590 °C for 18 h, the average grain size of HE (Y 0.2 Yb 0.2 Lu 0.2 Eu 0.2 Er 0.2 ) 3 Al 5 O 12 increases only from 1.56 μm to 2.27 μm. Close thermal expansion coefficient to TG Al 2 O 3 , low thermal conductivity, good phase stability, excellent chemical compatibility with TG Al 2 O 3 and slow grain growth rate make HE (Y 0.2 Yb 0.2 Lu 0.2 Eu 0.2 Er 0.2 ) 3 Al 5 O 12 promising for thermal barrier applications.