Preparation and dielectric property of BaTiO3-SrTiO3 artificially modulated structures

In order to elucidate the origin of the asymmetry observed in the D-E or C-V hysteresis loops of BaTiO3 (BTO)-SrTiO3 (STO) epitaxial films, "artificially modulated structures" (AMSs), where the chemical composition was continuously changed along the direction of film thickness, were prepared and their dielectric properties were measured. A fully automatic molecular beam epitaxy system was developed to fabricate AMSs. Two kinds of AMS, (BTO<--STO) and (STO<--BTO) where Ba/Sr ratios were changed from the film/substrate interface to the film surface in the reverse direction, were prepared on Nb-doped STO single crystals. The simulation of XRD profiles indicated that a relaxation of the crystal lattice occurred along the a-axis in the two AMSs, and the degree of the relaxation was more significant in (BTO<--STO)AMS. It was observed that the asymmetry of the C-V hysteresis loop was changed by the modulation of chemical composition, and that the origin of the asymmetry was attributed to the lattice relaxation rather than the asymmetry of the stress field.