Unveiling surface stability and oxygen vacancy segregation of Yb2SiO5 and Lu2SiO5 by first‐principles calculations.

RE2SiO5 (RE = Yb and Lu) are significant environmental barrier coating (EBC) materials, in which surface and oxygen vacancy play crucial roles in their structural stability and functionality. In this work, the structural configuration and thermodynamics of (1 0 0), (0 1 0), and (0 0 1) surfaces of RE2SiO5 are investigated by first‐principles calculations. The (0 0 1) surface is preferred energetically, which is attributed to the weak bond broken environment and large rare‐earth polyhedron distortion on this surface. Moreover, the formation energies of various oxygen vacancies on the stable (0 0 1) surface are estimated and the optimal location for oxygen vacancies is held by the [SiO4] tetrahedron. The oxygen vacancies are more likely to segregate on the surface because of the lower formation energies on the surfaces compared with those in the bulk. These findings are expected to enable the development of RE2SiO5‐based EBCs by tuning grain size and/or thin film growth orientation. [ABSTRACT FROM AUTHOR]