Yttrium segregation and surface phases of yttria-stabilized zirconia (1Â 1Â 1) surface

Surface segregation of yttria-stabilized zirconia (YSZ) was studied via first-principles computations and thermodynamics. For the cubic YSZ (1 1 1) surface, yttrium can segregate only to a subsurface layer, and these segregation phases are terminated at the surface by defective oxygen layers with honeycomb structure. The segregation is independent of the bulk yttrium concentration at high oxygen partial pressures or low temperatures. At very low oxygen partial pressures and high temperatures there is no surface yttrium segregation and the surface is terminated by O-Zr. Our results provide a reasonable explanation for previous experimental work, and also a framework for extending our understanding of cation segregation in oxide surfaces.