DISLOCATIONS IN PBTIO3 THIN-FILMS

Using conventional and high resolution transmission electron microscop y, the dislocation structures in PbTiO3 thin films grown epitaxially o n [001]-oriented MgO and SrTiO3 single crystals are studied. High reso lution cross-sectional images of the films grown on MgO exhibit misfit dislocations with Burgers vectors of 1/2 [010] and line directions of [100]. The latter are identified by imaging the interface in two non- parallel zone axes. Plan-view studies of films grown on SrTiO3 reveal dislocations with Burgers vectors of [010] lying along [100] direction s in the plane of the film. High resolution microscopy of cross-sectio nal samples shows dislocations in these films that have the additional half-plane on the substrate side of the film, opposite to what is req uired to accommodate the lattice misfit at room temperature. The mecha nisms for dislocation formation and the role of the dislocations in st ress relaxation with respect to the competing mechanism of 90-degrees domain formation are discussed.