Effect of a single dislocation in a heterostructure layer on the local polarisation of a ferroelectric layer
IFF-News March 1, 2009
by C.L. Jia, S.B. Mi, K. Urban, I. Vrejoiu, M. Alexe, and D. Hesse
Owing to their excellent properties, perovskite ferroelectrics have become important materials in electronics applications. In more complex systems like perovskite ferroelectric-paraelectric superlattices or tricolor superlattices intriguing properties and effects arise due to the combination of materials with similar structure. Adjusting the composition/periodicity in these superlattices allows for an additional degree of freedom and results in the possibility to tune the final properties. As has recently been shown, a classical ferroelectric-paraelectric system, such as PbTiO/SrTiO can, under certain conditions, behave like an improper ferroelectric only due to a ferroelectric/antiferrodistortive coupling at the interface between the two materials. In experimental and theoretical analysis of these effects one usually assumes that one is dealing with perfect materials. Oxides and, in particular, ferroelectric perovskite oxides are, however, far from being perfect materials. When the characteristic sizes of the investigated systems are scaling down to nanometre sizes even a single lattice defect can be very detrimental to ferroelectric properties. An example is the case of dislocations that are not avoidable in most crystalline materials. In the surrounding area a dislocation produces strain which depends on the Burgers vector of the dislocation.
In the present study, the influence of a single dislocation in a SrTiO sublayer on the local ferroelectric polarisation of the neighboring ferroelectric PbZrTiO (PZT) sublayer in an epitaxial SrTiO/PbZrTiO/SrTiO three-layer heterostructure has been studied on the atomic scale. The strain field of the dislocation in the SrTiO layer propagates across the interface into the PZT layer and leads to a strong variation of the c-axis lattice parameter of the PZT layer. Accompanying a strong reduction of the c-axis lattice parameter, the offcentre displacements of the Zr/Ti atoms away from the centre of the oxygen octahedra are also strongly decreased, resulting in a decrease of the local spontaneous polarisation by up to 48%.
C.L. Jia, S.B. Mi, K. Urban, I. Vrejoiu, M. Alexe, and D. Hesse: Effect of a Single Dislocation in a Heterostructure Layer on the Local Polarisation of a Ferroelectric Layer, Phys. Rev. Lett. 102 (2009) 117601.