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 with thermomechanical robustness against calcium-magnesium-aluminum-silicate deposits are in high demand. The aim of this work is to clarify the influence of Sc³⁺ on 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⁺ tend to form [BO₆] coordination polyhedron in crystal structure to promote the formation of garnet and diopside, while Yb³⁺ occupy 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) pseudo-ternary phase diagram is established, which has a great potential to describe phase equilibrium in coating-deposit systems and can provide guidance for compositional design of corrosion-resistant coatings.