Enhancing piezoelectricity through polarization-strain coupling in ferroelectric superlattices

Short-period ferroelectric/ferroelectric PbTiO3 (PTO)/ BaTiO3 (BTO) superlattices are studied using density functional theory. Contrary to the trends in paraelectric/ferroelectric superlattices the polarization remains nearly constant for PTO concentrations below 50%. In addition, a significant decrease in the c/a ratio below the PTO values was observed. Using a first-principles superlattice model we predict an enhancement in the d33 piezoelectric coefficient peaking at ∼75% PTO concentration due to the different polarization-strain coupling in PTO and BTO layers. Further analysis reveals that these trends are bulk properties which are a consequence of the reduced P brought about by the polarization saturation in the BTO layers.