We studied the size dependence of the ferroelectric domain structure in unique free-standing PbTiO 3 thin film, composed of grains 60-1000 nm in size, with transmission-electron microscopy. With such samples, we showed that the apparent dependence of electrical properties on the thickness of polycrystalline thin films stems from their grain-size dependence. We found that a domain-structure transition, from predominantly multidomain to predominantly single domain occurs at a grain size of ϳ150 nm ͑corresponding to a thickness 200-300 nm͒. Based on these experimental results, the drastic change of coercive field and dielectric permittivity below a thickness 200-300 nm was reasonably explained as resulting from a domain-structure transition.

Thin YBa2Cu3O7−δ∕La0.67Ca0.33MnO3∕YBa2Cu3O7−δ (YBCO/LCMO/YBCO) trilayers on (001)-oriented SrTiO3 (STO) substrates were fabricated by magnetron sputtering technique. The trilayers are well c-axis oriented confirmed by x-ray diffraction. The surface and interface structure of the trilayers were investigated by grazing incident x-ray reflectivity. The results showed that there exists diffusion at the YBCO/LCMO interfaces with the diffusion length of several nanometers. The root-mean-square (rms) roughness of surface and interface in the trilayers varied with the thickness of YBCO layer. The rms roughness of surface was consistent with observation by atomic force microscopy. A further analysis indicated that the rms roughness was correlative to the misfit strain relaxation in film.