Unusual behaviour of the ferroelectric polarization in PbTiO${}_3$/SrTiO${}_3$ superlattices

Abstract

Artificial PbTiO${}_3$/SrTiO${}_3$ superlattices were constructed using off-axis RF magnetron sputtering. X-ray diffraction and piezoelectric atomic force microscopy were used to study the evolution of the ferroelectric polarization as the ratio of PbTiO${}_3$ to SrTiO${}_3$ was changed. For PbTiO${}_3$ layer thicknesses larger than the 3-unit cells SrTiO${}_3$ thickness used in the structure, the polarization is found to be reduced as the PbTiO${}_3$ thickness is decreased. This observation confirms the primary role of the depolarization field in the polarization reduction in thin films. For the samples with ratios of PbTiO${}_3$ to SrTiO${}_3$ of less than one a surprising recovery of ferroelectricity that cannot be explained by electrostatic considerations was observed.