Insight on the ferroelectric properties in a (BiFeO3)2(SrTiO3)4 superlattice from experiment and ab initio calculations

Abstract

Ferroelectric domain properties of a (BiFeO3)2(SrTiO3)4 superlattice were studied by means of piezoresponse force microscopy and density functional theory calculations. A combination of out-of-plane and in-plane piezoresponse force imaging confirms that the ferroelectric domains are oriented along the out-of-plane [001] direction of the film. Density functional theory calculations evidence that this orientation is due to the tetragonal-like structure adopted by the BiFeO3 units inside the superlattice in response to the interfacial strains. In addition, antiferrodistortive rotations of the BO2 planes within both types of ABO3 blocks (i.e., SrTiO3 as well as BiFeO3 units) are highlighted. Besides, a much lower coercive voltage is measured on superlattices compared to BiFeO3 single layers, suggesting a more reliable switching capability. The results are expected to enable the design of promising multifunctional oxide superlattices.