Density-functional theory study of polarization saturation in strained ferroelectrics

Abstract

Using density-functional calculations and the modern theory of polarization, we study the structure and polarization responses of tetragonal ${\text{PbTiO}}_{3}$, ${\text{BaTiO}}_{3}$, and ${\text{SrTiO}}_{3}$ in a strain regime that is previously overlooked. We find that the ${\ensuremath{\chi}}_{3}$ polarizations in all three substances saturate at large strains, revealing a phenomenon that is generally applicable. The saturation demonstrates the existence of a sophisticated collective behavior in the large-strain regime and is shown to originate possibly from electron-ion correlation that leads to a cancellation between electronic and ionic polarizations. Our results shed insight on the polarization properties and provide explanations for the puzzling results recently observed in experiments.