Structure, lattice dynamics, properties of bismuth titanate heterostructures

We investigated the epitaxial Bi4Ti3O12 (BTO) thin films with different thicknesses on a (0 0 1) MgO substrate with a Ba0.4Sr0.6TiO3 buffer layer (4 nm). The crystallographic axis [1 0 0] of Bi4Ti3O12 film is rotated on degrees relative to [1 0 0] MgO axis. When the thickness of Bi4Ti3O12 film is less than 40 nm, the unit cell of the film is compressed in the normal to the interface plane direction. In cases of large film thicknesses, the sign of strain changes and correspondingly the unit cell is stretched. Switched spontaneous polarization in the interface plane with 180° domain structure occurs at 10 nm film thickness and increases with a thickness up to 55 C cm−2. Changes in the Raman spectra of the Bi4Ti3O12 films indicates to increase of monoclinic distortion of the film unit cell in comparison with the bulk unit cell. The anisotropy of in-plane dielectric properties and the effect of internal strain on dielectric properties for the Bi4Ti3O12 films are confirmed by the study of the dielectric characteristics of the films.