Topological phase transformations and intrinsic size effects in ferroelectric nanoparticles

John Mangeri; Yomery Espinal; Andrea Jokisaari; S Pamir Alpay; Serge Nakhmanson; Olle Heinonen

doi:10.1039/c6nr09111c

Topological phase transformations and intrinsic size effects in ferroelectric nanoparticles

Nanoscale. 2017 Jan 26;9(4):1616-1624. doi: 10.1039/c6nr09111c.

Authors

John Mangeri¹, Yomery Espinal², Andrea Jokisaari³, S Pamir Alpay⁴, Serge Nakhmanson⁴, Olle Heinonen⁵

Affiliations

¹ Department of Physics, University of Connecticut, Storrs, CT, USA. john.mangeri@uconn.edu.
² Department of Materials Science and Engineering, University of Connecticut, Storrs, CT, USA.
³ Center for Hierarchical Material Design, Northwestern-Argonne Institute of Science and Engineering, Northwestern University, Evanston, IL, USA. heinonen@anl.gov.
⁴ Department of Physics, University of Connecticut, Storrs, CT, USA. john.mangeri@uconn.edu and Department of Materials Science and Engineering, University of Connecticut, Storrs, CT, USA and Institute of Materials Science, University of Connecticut, Storrs, CT, USA.
⁵ Center for Hierarchical Material Design, Northwestern-Argonne Institute of Science and Engineering, Northwestern University, Evanston, IL, USA. heinonen@anl.gov and Material Science Division, Argonne National Laboratory, Lemont, IL, USA.

PMID: 28074199
DOI: 10.1039/c6nr09111c

Abstract

Composite materials comprised of ferroelectric nanoparticles in a dielectric matrix are being actively investigated for a variety of functional properties attractive for a wide range of novel electronic and energy harvesting devices. However, the dependence of these functionalities on shapes, sizes, orientation and mutual arrangement of ferroelectric particles is currently not fully understood. In this study, we utilize a time-dependent Ginzburg-Landau approach combined with coupled-physics finite-element-method based simulations to elucidate the behavior of polarization in isolated spherical PbTiO₃ or BaTiO₃ nanoparticles embedded in a dielectric medium, including air. The equilibrium polarization topology is strongly affected by particle diameter, as well as the choice of inclusion and matrix materials, with monodomain, vortex-like and multidomain patterns emerging for various combinations of size and materials parameters. This leads to radically different polarization vs. electric field responses, resulting in highly tunable size-dependent dielectric properties that should be possible to observe experimentally. Our calculations show that there is a critical particle size below which ferroelectricity vanishes. For the PbTiO₃ particle, this size is 2 and 3.4 nm, respectively, for high- and low-permittivity media. For the BaTiO₃ particle, it is ∼3.6 nm regardless of the medium dielectric strength.