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Vortex Polarization Instabilities in PbTiO3 Nanowires
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Vortex Polarization Instabilities in PbTiO3 Nanowires

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  • 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 nanostructuresProsendeev & 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 StudyAxial polarization Vortex polarizationinstability above instability above1.2 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. TerminationsStrain-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. SummaryPbTiO3 nanowires display switchable rectilinear (axial) and non-rectilinear (vortex) polarization configurations

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