vortex polarization instabilities in pbtio3 nanowires

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

Ferroelectricity in Nanostructures Critical Size & Polarization States

Lateral Polarization in BaTiO3 nanowires Spanier et al, Nano Lett. 6, 735 (2006)

0.8 nm

Ferroelectric Nanostructures Vortex (Non-rectilinear) Polarization

PFM results indicate possible presence of non-rectilinear polarization in PZT nanodots

Rodriguez et al (Nanoletters, 2009)

Prosendeev & Bellaiche (PRB 2007)

Aguado-Puente et al (PRL, 2008)

Computations indicate the presence of non-rectilinear polarization in ferroelectric nanostructures

BaTiO3 Nanowires – Our DFT Study

Axial polarization instability above 1.2 nm

ferroelectric paraelectric

Vortex polarization instability above 1.6 nm

Also see: Geneste et. al, APL 88, 112906 (2006); Shimada et al, PRB 79, 024102 (2009)

PbTiO3 Nanowires – Our DFT Study Vortex polarization at

equilibrium in TiO2-terminated nanowires above 1.6 nm

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

PbTiO3 Nanowires vs. Terminations Strain-induced phase transition: vortex axial polarization

Four possible switchable polarization states Vortex (clockwise/counter-clockwise), Axial (positive/negative)

Vortex Instability vs. “Soft-mode”

Atomic displacement vector with respect to reference

paraelectric state

Zone-center phonon eigenvectors of reference

paraelectric state

“Vortex” modes: imaginary

Summary PbTiO3 nanowires display switchable rectilinear (axial) and

non-rectilinear (vortex) polarization configurations