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Three kinds of high entropy (Y 0.25 Sc 0.25 Er 0.25 Yb 0.25) 2 Si 2 O 7 , (Y 0.2 Sc 0.2 Er 0.2 Yb 0.2 Lu 0.2) 2 Si 2 O 7 and (Y 0.2 Sc 0.2 Er 0.2 Yb 0.2 Gd 0.2) 2 Si 2 O 7 were designed and synthesized in order to investigate the relation of microstructures and CMAS corrosion resistance. At low temperature of 1300 °C, lattice distortion played a crucial role in resistance to CMAS corrosion, and larger lattice distortion contributed to CMAS corrosion resistance. However, the corrosion behavior at 1500 °C was related to the equivalent ionic radius and RE species. The smaller equivalent ionic radius tended to promote the re-precipitation of high entropy RE disilicate in residual CMAS glass rather than apatite. The results will provide theoretical guidance for the microstructural design of high entropy RE disilicate and selection of RE elements in future. • High entropy ceramics were synthesized by solid state reaction method. • (Y 0.2 Sc 0.2 Er 0.2 Yb 0.2 Gd 0.2) 2 Si 2 O 7 ceramics had a maximum lattice distortion. • (Y 0.2 Sc 0.2 Er 0.2 Yb 0.2 Gd 0.2) 2 Si 2 O 7 presented a best CMAS corrosion resistance. [ABSTRACT FROM AUTHOR]

The novel rare earth monosilicates (xRE 1/x) 2 SiO 5 (RE=Yb, Tm, Er, Y, Dy and Tb, x = 2–6) were prepared in order to establish the relationship between configurational entropy and lattice distortion, and the effect of configurational entropy on their properties was investigated. The results showed that the lattice distortion of (xRE 1/x) 2 SiO 5 increased gradually with the increase of configurational entropy, but the multi-principal component solid solution tended to form a highly symmetrical crystal structure when the configurational entropy was large enough, thus inhibiting the lattice distortion. (5RE 1/5) 2 SiO 5 had a maximum lattice distortion, which leaded to a relatively low thermal conductivity and coefficient of thermal expansion, and good CMAS corrosion resistance. • The effect of configurational entropy on microstructure and properties was investigated. • (5RE 0.2) 2 SiO 5 ceramic had a maximum lattice distortion. • (5RE 0.2) 2 SiO 5 ceramic presented the relatively good thermal properties and CMAS corrosion resistance. [ABSTRACT FROM AUTHOR]