The influence of yttria-stabilized zirconia surface pits on the initial stage of reactive La₂Zr₂O₇ formation from La₂O₃ vapours and yttria-stabilized zirconia (001) substrates

The initial stage of La₂Zr₂O₇ (LZO) formation by an interfacial solid state reaction between yttria-stabilised zirconia (YSZ) and La₂O₃ is experimentally investigated. LZO islands are formed on YSZ(001) single-crystal surfaces exposed to La₂O₃ vapours when a high density of pits are present on the YSZ surface. Compared with the previously studied formation of almost epitaxial La₂Zr₂O₇ islands on a perfectly plane YSZ surface, characteristic differences and new features are found, which are explained by the influence of the pit rims. Whereas islands growing far away from a pit have a regular structure and consist of four <110>-tilted domains, islands growing near a pit involve a central hole and consist of two to four <100>-tilted stripe domains in addition to the four regular <110>-tilted domains. The new stripe domains contain two orthogonal sets of misfit dislocations: one of a Burgers vector with a component perpendicular to the interface plane, and the other of an in-plane Burgers vector. These new features are explained in terms of the preferred nucleation of LZO islands near the pit and their specific growth kinetics under the influence of the pit rim, where the stresses arising in the growing islands are partially relaxed by the deformation of the pit rim.