Environmental barrier coatings (EBCs) with thermomechanical robustness against calcium–magnesium–aluminum–silicate (CMAS) deposits are in high demand. The aim of this work was to clarify the influence of Sc³⁺ on the crystallization behavior of Yb-based coatings against CMAS deposits. The reaction products of solid solutions with compositions traversing the Sc₂O₃–Yb₂O₃ system indicate that Sc³⁺ tends to form [BO₆] coordination polyhedra in the crystal structure to promote the formation of garnet and diopside, while Yb³⁺ occupies 7-, 8-, and 9-coordinate sites to crystallize apatite and silicocarnotite. The transformation of crystalline products from apatite/silicocarnotite to garnet/diopside greatly improves the efficiency of CMAS melt consumption and facilitates the prevention of its further penetration and corrosion. Based on the commonality of cation occupancy in crystallography, an A(CaO+YbO_1.5)–B(ScO_1.5+MgO+AlO_1.5)–T(SiO₂) pseudoternary phase diagram is established, which has great potential for describing phase equilibrium in coating-deposit systems and can provide guidance for the compositional design of corrosion-resistant coatings.

Model composites consisting of SiC fiber and Yb₂SiO₅ were processed by the spark plasma sintering (SPS) method. The mechanical compatibility and chemical stability between Yb₂SiO₅ and SiC fiber were studied to evaluate the potential application of Yb monosilicate as the interphase of silicon carbide fiber reinforced silicon carbide ceramic matrix composite (SiC_f/SiC CMC). Two kinds of interfaces, namely mechanical and chemical bonding interfaces, were achieved by adjusting sintering temperature. SiC_f/Yb₂SiO₅ interfaces prepared at 1450 and 1500 ℃ exhibit high interface strength and debond energy, which do not satisfy the crack deflection criteria based on He–Hutchison diagram. Raman spectrum analyzation indicates that the thermal expansion mismatch between Yb₂SiO₅ and SiC contributes to high compressive thermal stress at interface, and leads to high interfacial parameters. Amorphous layer at interface in model composite sintered at 1550 ℃ is related to the diffusion promoted by high temperature and DC electric filed during SPS. It is inspired that the interfacial parameters could be adjusted by introducing Yb₂Si₂O₇–Yb₂SiO₅ interphase with controlled composition to optimize the mechanical fuse mechanism in SiC_f/SiC CMC.