Using density-functional calculations we study the structure and polarization response of tetragonal PbTiO3, BaTiO3 and SrTiO3 in a strain regime that is previously overlooked. Different from common expectations, we find that the polarizations in all three substances saturate at large strains, demonstrating a universal phenomenon. The saturation is shown to originate from an unusual and strong electron-ion correlation that leads to cancellation between electronic and ionic polarizations. Our results shed new insight on the polarization properties, and reveal the existence of a fundamental limit to the strain-induced polarization enhancement.
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