Atomic-scale understanding of enhanced polarization of highly strained nanoscale columnar PbTiO3

Spontaneous polarization in displacive ferroelectric oxides originates from the separation of positive charge centers from negative charge centers, which is induced by the off-center displacements of cations and anions in unit cells. For hugely strained ferroelectric oxides, understanding the correlation between the off-center displacements and the strain level is a prerequisite for understanding the polarization behavior. In the present work, the off-center displacements of atoms in nanometer columnar PbTiO3 under a strong tensile strain of 13% along the c-axis direction are quantified by quantitative high-resolution transmission electron microscopy. The measured off-center displacement ΔTi-O (0.052 nm) is about 60% larger than the value of unstrained bulk PbTiO3. The experimental results are confirmed by first-principle calculations, leading to a polarization of 122μC/cm2, providing the basis for understanding the enhanced spontaneous polarization of highly strained displacive ferroelectric oxides.