Large nonlinear dielectric properties of artificial BaTiO ₃/SrTiO₃ superlattices

BaTiO₃(BTO)/SrTiO₃(STO) artificial superlattices have been made on MgO (100) substrates. The periodicity of the BTO/STO layers in the superlattice was varied from one-unit cell to 125-unit cell thickness. The dielectric constant and its nonlinearity (or voltage tunability) showed similar behavior as the periodicity was varied. The voltage tunability of the superlattice increased with decreasing stacking periodicity of the BTO/STO within the critical thickness. Similarly, the lattice distortion, i.e., the ratio of the lattice parameter along surface normal to parallel, of the BTO and STO layers increased with decreasing the periodicity. Remarkable enhancement of the voltage tunability has been achieved. The superlattice exhibited large voltage tunability (94%, the highest value to date) at the periodicity of BTO_2-unitcell/STO_2-unitcell at which the maximum lattice distortion of each layer was obtained. This suggests that the nonlinear dielectric property of the superlattice is closely related with the lattice distortion of the individual layers.