Polarization and Dielectric Properties of BiFeO(3)-BaTiO(3) Superlattice-Structured Ferroelectric Films

Superlattice-structured epitaxial thin films composed of Mn(5%)-doped BiFeO(3) and BaTiO(3) with a total thickness of 600 perovskite (ABO(3)) unit cells were grown on single-crystal SrTiO(3) substrates by pulsed laser deposition, and their polarization and dielectric properties were investigated. When the layers of Mn-BiFeO(3) and BaTiO(3) have over 25 ABO(3) unit cells (N), the superlattice can be regarded as a simple series connection of their individual capacitors. The superlattices with an N of 5 or less behave as a unified ferroelectric, where the BaTiO(3) and Mn-BiFeO(3) layers are structurally and electronically coupled. Density functional theory calculations can explain the behavior of spontaneous polarization for the superlattices in this thin regime. We propose that a superlattice formation comprising two types of perovskite layers with different crystal symmetries opens a path to novel ferroelectrics that cannot be obtained in a solid solution system.