First-principles calculations are used to predict properties of (001) epitaxial, short-period PbTiO${}_3$/BiFeO${}_3$ superlattices (SL) as a function of the in-plane lattice constant. These heterostructures exhibit original phenomena, such as three strain-driven isostructural phase transitions (two being of first order and one being of second order); five equilibrium phases that all differ in symmetry from those found in the pure PbTiO${}_3$ (PTO) and BiFeO${}_3$ (BFO) films; and the presence of significant oxygen octahedra tiltings in the PTO layers of the superlattice within a broad range of epitaxial strain values. All these unusual features can be understood from (i) the knowledge of the corresponding phases in the pure PTO and BFO films; (ii) the requirement that the out-of-plane component of the “formal” polarization (including ferroelectric and compositional dipoles) be homogeneous inside the superlattice; and (iii) the competition between polarization and oxygen octahedral tilting, in the presence of electrostatic couplings and interfacial proximity effects.

• Received 8 August 2012

DOI:https://doi.org/10.1103/PhysRevB.86.144114