Green preparation of high entropy ceramics (Y0.2Sm0.2Eu0.2Er0.2Yb0.2)2SiO5 with low thermal conductivity by molten salt synthesis

High entropy rare earth silicate ceramics have been widely studied as potential material for environmental barrier coatings (EBCs). At present, the synthesis method of high entropy rare earth silicate ceramics is generally solid state reaction method, which has some problems such as high energy consumption, low efficiency and low purity of synthesized products. In order to solve these problems, high entropy (Y0.2Sm0.2Eu0.2Er0.2Yb0.2)2SiO5 was prepared by molten salt synthesis (MSS). By adjusting the reaction temperature and the amount of molten salt, it was found that the pure high entropy (Y0.2Sm0.2Eu0.2Er0.2Yb0.2)2SiO5 ceramic powders could be synthesized at 1400 degrees C when Na2SO4 and K2SO4 are selected as molten salts(Na+:K+ = 1:1), and the mass ratio of molten salt to reactant is 1: 1. The molten salt synthesis significantly reduced the reaction temperature and accelerated the reaction rate. The prepared high entropy (Y0.2Sm0.2Eu0.2Er0.2Yb0.2)2SiO5 has a monoclinic X2type Re2SiO5 structure and a low thermal conductivity of 0.96 +/- 0.03 W m-1 K-1 due to the high entropy effect. This can be explained by the existence of high concentration oxygen vacancies and the highly disordered arrangement of multicomponent cations in a unique high entropy configuration. This material also shows good infrared reflectance, which makes (Y0.2Sm0.2Eu0.2Er0.2Yb0.2)2SiO5 a potential environmental barrier coating material.