Engineered polarization rotation in PbTiO$_{3}$/CaTiO$_{3}$ superlattices

Large piezoelectric responses, such as those seen in PbZr$_{x}$Ti$_{1-x}$O$_{3}$ in the vicinity of the compositional morphotropic phase boundary, can occur when the direction of the polarization in a ferroelectric material can rotate. Here we show experimentally that a similar enhancement of the piezoelectric response can be achieved in artificially layered epitaxial superlattices composed of alternating layers of PbTiO$_{3}$ and CaTiO$_{3}$ deposited on SrTiO$_{3}$ substrates by RF magnetron sputtering. The exceptional quality of our samples is demonstrated by x-ray diffraction and transmission electron microscopy. The structural and functional properties of the materials have been measured as a function of relative layer thickness. Electrically measured ferroelectric polarization and dielectric constants corroborate the enhancement of d$_{33}$ we have measured experimentally using piezoforce microscopy. The structural changes, which allow polarization rotation, have been directly measured using grazing incidence in-plane x-ray diffraction (at NSLS X21 and X22C). Finally, the as-grown domain structure has been imaged with piezoforce microscopy, further confirming polarization rotation and explaining the unusual switching dynamics observed in our electrical characterization.