1 research outputs found
Polarization Rotation in Ultrathin Ferroelectrics Tailored by Interfacial Oxygen Octahedral Coupling
Multiple polar states and giant piezoelectric
responses could be driven by polarization rotation in ferroelectric
films, which have potential functionalities in modern material applications.
Although theoretical calculations have predicted polarization rotation
in pure PbTiO<sub>3</sub> films without domain walls and strains,
direct experiment has rarely confirmed such polar states under this
condition. Here, we observed that interfacial oxygen octahedral coupling
(OOC) can introduce an oxygen octahedral rotation, which induces polarization
rotation in single domain PbTiO<sub>3</sub> films with negligible
strains. We have grown ultrathin PbTiO<sub>3</sub> films (3.2 nm)
on both SrTiO<sub>3</sub> and Nb:SrTiO<sub>3</sub> substrates and
applied aberration-corrected scanning transmission electron microscopy
(STEM) to study the interfacial OOC effect. Atomic mappings unit cell
by unit cell demonstrate that polarization rotation occurs in PbTiO<sub>3</sub> films on both substrates. The distortion of oxygen octahedra
in PbTiO<sub>3</sub> is proven by annular bright-field STEM. The critical
thickness for this polarization rotation is about 4 nm (10 unit cells),
above which polarization rotation disappears. First-principles calculations
manifest that the interfacial OOC is responsible for the polarization
rotation state. These results may shed light on further understanding
the polarization behavior in ultrathin ferroelectrics and be helpful
to develop relevant devices as polarization rotation is known to be
closely related to superior electromechanical responses