ATOMISTIC STRUCTURE OF MISFIT DISLOCATIONS IN SrZrO_3/SrTiO_3 INTERFACES

摘要

The atomistic structure of misfit dislocations at heterointerfaces between two ionic crystals with the perovskite structure, SrZrO_3 and SrTiO_3, is investigated. The interfaces were fabricated by metal or- ganic deposition of SrZrO_3 layers on (00l) SrTiO_3 single crystal substrates. Under appropriate conditions the SrZrO_3 layer grows epitaxially. with its crystal lattice parallel to the lattice of the substrate ("cube-on- cube" orientation relationship). In the layer/substrate interface a square network of dislocations accommo- dates the misfit between corresponding spacings in the two crystals. These misfit dis1ocations have edge character, (0l0) line directions, and (100) Burgers vectors parallel to the interface. The SrZrO_3/SrTiO_3 interface has been imaged with the misfit dislocations in end-on projection by high-resolution transmission electron microscopy and also by high-resolution scanning transmission electron microscopy. Quantitative image analysis has shown that a (002) layer of TiO_2 terminates the SrTiO_3 crystal, and the SrZrO_3 crystal commences with a (002) layer of Sr O. Concerning the {200} layers normal to the interface it was found that in interface regions of good match, between the misfit dislocations, the perovskite structure continues straight through the interfaces Sr-O layers of SrTiO_3 continue as Sr_ O layers of SrZrO_3, and TiO_2 layers continue as ZrO_2 layers. Where the misfit dislocations reside, however, in regions of poor match, a lateral offset exists between the two crystals and disrupts the perovskite structure on the core plane (the symmetry plane) of the misfit dislocations a (200) TiO_2 1ayer of SrTiO_3 continues as a (200) SrO layer in SrZrO_3