Coexistence of antiferrodistortive and ferroelectric distortions at thePbTiO3(001)surface

Abstract

The c(2×2) reconstruction of (001) PbTiO3 surfaces is studied by means of first principles calculations for paraelectric (non-polar) and ferroelectric ([001] polarized) films. Analysis of the atomic displacements in the near-surface region shows how the surface modifies the antiferrodistortive (AFD) instability and its interaction with ferroelectric (FE) distortions. The effect of the surface is found to be termination dependent. The AFD instability is suppressed at the TiO2 termination while it is strongly enhanced, relative to the bulk, at the PbO termination resulting in a c(2x2) surface reconstruction which is in excellent agreement with experiments. We find that, in contrast to bulk PbTiO3, in-plane ferroelectricity at the PbO termination does not suppress the AFD instability. The AFD and the in-plane FE distortions are instead concurrently enhanced at the PbO termination. This leads to a novel surface phase with coexisting FE and AFD distortions which is not found in PbTiO3 bulk.

Novel high-temperature ferroelectric domain morphology in PbTiO3 ultrathin films

“…We used the adiabatic core-shell forcefield derived in Gindele et al, that reproduces the structural parameters of the cubic and tetragonal phases, the Born effective charge tensors, the elastic properties and soft phonon modes of PbTiO 3 in excellent agreement with density functional theory (DFT) calculations [25]. Furthermore, the model correctly describes the enhanced antiferrodistortive c(2x2) surface relaxation of PbTiO 3 in agreement with ab initio calculations [26,27].…”

“…It has recently been proposed that control of AFD chiralities could be used in novel technologies such as four-state memory making the identity of methods to control AFD behaviour at atomic scales paramount [45]. Here, we demonstrate the effects of ferroelectric-antiferrodistortive coupling between the c(2x2) AFD surface reconstruction and the ferroelectric (FE) closure domain patterns at the surface of the PbTiO 3 film [26,27]. This is characterised by the rotation of the equatorial oxygen atoms about the titanium, with simultaneous out-of-plane distortions which vary along the direction of the domain wall normals For the c d domains a sinusoidal dependence is noted with a maximum rotation at the centre of the domain when the polarisation is pointing out-of-plane and minimised when the polarisation points into the plane (Figure 5a).…”

Ab initiocalculations ofBaTiO3andPbTiO

“…1,2 Therefore, it is not surprising that a large number of ab initio quantum mechanical calculations, 3,4,5,6,7,8,9,10,11,12,13 as well as several classical shell-model (SM) studies, 14,15,16 have dealt with the atomic and electronic structure of the (001) surface of BaTiO 3 , PbTiO 3 , and SrTiO 3 crystals. In order to study the dependence of the surface relaxation properties on the exchange-correlation functionals and the type of basis (localized vs. plane-wave) used in the calculations, a detailed comparative study of SrTiO 3 (001) surfaces based on ten different quantum-mechanical techniques 17,18 was recently performed.…”

Direct evidence for ferroelectric polar distortion in ultrathin lead titanate perovskite films

“…The atomic positions were then relaxed until the maximum residual atomic force was smaller than 40 meV/Å. Our calculations were restricted to (1 × 1) surface periodicity and did not allow for an eventual antiferrodistortive (AFD) c(2 × 2) reconstruction [22,23]. The latter is not excluded but, as discussed later, was not evidenced on our films at room temperature.…”