  The possibility of controlling the domain structure in spherical
nanoparticles of uniaxial and multiaxial ferroelectrics using a shell with
tunable dielectric properties is studied in the framework of
Landau-Ginzburg-Devonshire theory. Finite element modeling and analytical
calculations are performed for Sn2P2S6 and BaTiO3 nanoparticles covered with
high-k polymer, temperature dependent isotropic paraelectric strontium
titanate, or anisotropic liquid crystal shells with a strongly temperature
dependent dielectric permittivity tensor. It appeared that the tunable
paraelectric shell with a temperature dependent high dielectric permittivity
(~300 - 3000) provides much more efficient screening of the nanoparticle
polarization than the polymer shell with a much smaller (~10)
temperature-independent permittivity. The tunable dielectric anisotropy of the
liquid crystal shell (~ 1 - 100) adds a new level of functionality for the
control of ferroelectric domains morphology (including a single-domain state,
domain stripes and cylinders, meandering and labyrinthine domains, and
polarization flux-closure domains and vortexes) in comparison with isotropic
paraelectric and polymer shells. The obtained results indicate the
opportunities to control the domain structure morphology of ferroelectric
nanoparticles covered with tunable shells, which can lead to the generation of
new ferroelectric memory and advanced cryptographic materials.
