Domain Structure in Ferroelectric PbTiO3 Nano-islands

Evolution of complex ferroelastic domain structures of PbTiO₃ nano-islands grown epitaxially on Pt(001)/MgO(001) single crystal substrate by chemical solution deposition has been investigated by two-dimensional reciprocal space mapping technique using synchrotron X-ray diffraction. With decreasing lateral size and thickness of the nano-islands, the proportion of c-domains increased continuously and fully c-domain dominant structure was emerged. At the same time, some of a-domains in the twinned a/c/a/c type structure turned into the a-domains with defective domain boundaries aligned normal to the substrate plane. The relative proportions of two types of a-domains were also dependent on the lateral size of nano-islands. The smaller islands favored the aligned a-domains with defective domain boundaries, which seem to be due to extensive relaxation of confining strain imposed by the substrate.