Misfit Accommodation Mechanisms at Moving Reaction Fronts During the Initial Growth Stage of La2Zr2O7-based Pyrochlore on (001)YSZ

Abstract

AbstractLa2Zr2O7-based pyrochlore (LZO) islands were grown on (001)-oriented Y2O3-stabilized ZrO2 (YSZ) single crystal surfaces by the reaction between the crystals and a La2O3 vapour. The islands are epitaxial with a small tilt. On a flat substrate surface each pyramidal island consists of four domains which are slightly tilted around different <110> axes with respect to the YSZ lattice. On a YSZ surface with pits of high density, more interestingly, each larger island formed at a pit has a central hole and contains two to four <100>-tilted stripe domains in addition to the four regular <110>-tilted domains. A square network of interfacial edge dislocations having Bur- gers vectors as/2 [101] (as being the lattice parameter of YSZ) was observed in the regular domains at the LZO/YSZ reaction front of positive lattice mismatch (+5%). In stripe domains two sets of orthogonal misfit dislocations are present with different Burgers vectors of type b = as/2 [101] andas/2 [010]. The perpendicular components of the Burgers vectors give rise to the observed tilts of the LZO lattices. Possible models are proposed to explain the generation of dislocation half-loops, the preferred nucleation of the islands near YSZ surface pits as well as their growth kinetics and the formation of stripe domains.