1. Vortex Polarization Instabilities
in PbTiO3 Nanowires
G. Pilania and R. Ramprasad
Chemical, Materials and Biomolecular Engineering
Institute of Materials Science
University of Connecticut, Storrs, CT

2. Ferroelectricity in Nanostructures
Critical Size & Polarization States
Lateral Polarization in BaTiO3 nanowires
Spanier et al, Nano Lett. 6, 735 (2006)
0.8 nm

3. Ferroelectric Nanostructures
Vortex (Non-rectilinear) Polarization
Computations indicate the presence of non-rectilinear
polarization in ferroelectric nanostructures
Prosendeev & Bellaiche Aguado-Puente et al
(PRB 2007) (PRL, 2008)
PFM results indicate possible presence of non-rectilinear
polarization in PZT nanodots
Rodriguez et al
(Nanoletters, 2009)

4. BaTiO3 Nanowires – Our DFT Study
Axial polarization Vortex polarization
instability above instability above
1.2 nm 1.6 nm
paraelectric ferroelectric
Also see: Geneste et. al, APL 88, 112906 (2006);
Shimada et al, PRB 79, 024102 (2009)

5. PbTiO3 Nanowires – Our DFT Study
Vortex polarization at
equilibrium in TiO2-terminated
nanowires above 1.6 nm

6. Ground State Polarization & Atomic Configurations
4x4 TiO2-terminated PbTiO3 Nanowire

7. PbTiO3 Nanowires vs. Terminations
Strain-induced phase transition: vortex  axial polarization
Four possible switchable polarization states
Vortex (clockwise/counter-clockwise), Axial (positive/negative)

8. Vortex Instability vs. “Soft-mode”
Atomic displacement vector Zone-center phonon
with respect to reference eigenvectors of reference
paraelectric state paraelectric state
“Vortex” modes: imaginary

9. Summary
PbTiO3 nanowires display switchable rectilinear (axial) and
non-rectilinear (vortex) polarization configurations