Epitaxial short-period PbTiO3/BiFeO3superlattices studied by first-principles calculations

Abstract

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-ofplane 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 presence of electrostatic couplings and interfacial proximity effects.

Electrostatic engineering of strained ferroelectric perovskites from first principles

“…5. ) As before, the path described by the E z = 0 states (minimum energy configurations at a given value of a) is consistent with the results of earlier works [32,39]: (i) For a large range of in-plane strain values around the equilibrium parameter, BFO adopts a monoclinic Cc (we shall indicate this phase as Cc-I) state that is closely related to the bulk rhombohedral ground state. Here, both the polarization and the AFD − vector are large and roughly oriented along the (111) pseudocubic direction.…”

“…Second, our calculated phase diagram of Fig. 2 clearly shows that AFD − xy distortions do not occur in PTO at any value of a or D. Earlier literature studies [32,39,45] predicted such distortions to occur in the tensile-strain region, where the polarization vector has an in-plane orientation. (These structures were, therefore, identified as orthorhombic Ima2, rather than Amm2.)…”

“…(These structures were, therefore, identified as orthorhombic Ima2, rather than Amm2.) This discrepancy can be rationalized by observing that the AFD − xy mode amplitude was found [32,39,45] to be very small (i.e., ∼ 1…”

Large Elasto-Optic Effect in EpitaxialPbTiO3Films

“…An important reason for the choice of this particular system is that depending on the amount of misfit (tensile) strain they experience, these films can form (high-symmetry) tetragonal and orthorhombic states, but also low-symmetry, intermediate monoclinic phases [14,[26][27][28][29][30][31][32][33][34][35][36][37][38]. As we describe in the following, surprises are in store for this PTO system: the monoclinic phases are predicted to possess one of the largest elasto-optic coefficients ever reported.…”

Chemical strain-dependent two-dimensional transport at RAlO3/SrTiO3 interfaces (R=La,NdLi1, Yang2, Bai3 et al. 2016Phys. Rev. BSelf Cite6030View full textAdd to dashboardCite

“…This is in drastic contrast with cases of typical (001) ferroelectric films, such as BaTiO 3 , PbTiO 3 , and BiFeO 3 , in which the out-of-plane polarization decreases with the increase of tensile strain. [46][47][48][49] To further understand this increase of P i in (ReAO) 5 /(STO) 9 , it is informative to recall that one can also write that P i = ε 0 ε r E, where ε r is the dielectric constant and E is the electric field within the ReAO layers. For all the (ReAO) 5 /(STO) 9 supercell we considered, the ReAO thickness (5 u.c.)…”