Advances in Rare‐Earth Silicate Environmental Barrier Coatings

Rare‐earth silicates (RE 2 Si 2 O 7 and RE 2 SiO 5 ) are leading candidates for third‐generation environmental barrier coatings (EBCs) because they combine corrosion resistance to molten calcium–magnesium–aluminosilicate (CMAS) and high‐temperature water vapor with thermal expansion coefficients (CTEs) compatible with ceramic matrix composites (CMCs), high melting points, phase stability, and low thermal conductivity. Their composition–structure–property relationships nevertheless impose coupled constraints: a composition that stabilizes a desirable phase or lowers thermal conductivity does not necessarily maximize water‐vapor and CMAS resistance, and plasma‐sprayed coatings can differ substantially from dense bulk ceramics because of SiO 2 loss, amorphous phases, porosity, and segregation. Therefore, this review: (i) clarifies phase‐formation rules and their thermodynamic/crystallographic basis, (ii) compares single‐component and multicomponent silicates while distinguishing bulk and coating evidence, and (iii) summarizes environment‐dependent corrosion mechanisms and multi‐objective design strategies.