Vortex Polarization Instabilities in PbTiO3 Nanowires
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Transcript of Vortex Polarization Instabilities in PbTiO3 Nanowires
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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
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Ferroelectricity in Nanostructures Critical Size & Polarization States
Lateral Polarization in BaTiO3 nanowires Spanier et al, Nano Lett. 6, 735 (2006)
0.8 nm
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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
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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)
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PbTiO3 Nanowires – Our DFT Study Vortex polarization at
equilibrium in TiO2-terminated nanowires above 1.6 nm
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Ground State Polarization & Atomic Configurations 4x4 TiO2-terminated PbTiO3 Nanowire
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PbTiO3 Nanowires vs. Terminations Strain-induced phase transition: vortex axial polarization
Four possible switchable polarization states Vortex (clockwise/counter-clockwise), Axial (positive/negative)
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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
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Summary PbTiO3 nanowires display switchable rectilinear (axial) and
non-rectilinear (vortex) polarization configurations