Investigation on crystallization behavior between (Sc_xYb_1−x)O_1.5 and CMAS: A new insight in the effect of Sc substitution

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.