Topology of the polarization field in PbTiO 3 nanoparticles of different shapes by atomic-level simulations

DI RINO, F.; SEPLIARSKY, M.; STACHIOTTI, M. G.

JOURNAL OF APPLIED PHYSICS

AMER INST PHYSICS

Año: 2020 vol. 127

0021-8979

An atomistic model approach parameterized from first-principles calculations is used to investigate size and shape effects on the polarizationfield in isolated stress-free PbTiO3 nanoparticles. The study was carried out by molecular dynamics simulations in free-standing nanodotsof cylindrical, spherical, and ellipsoidal shapes. We show that in cylinders with diameter equal to height, the size-induced transformationfrom the vortex to the flux-closure domain configuration causes an anomaly in the behavior of the toroidal moment and the volume of thesystem. During this transformation, the vortex core evolves into domain walls while the resulting structure is stabilized due to the nonhomogeneousdistribution of polarization and strain inside the domains. A similar behavior is observed in elongated cylinders, spheres, andspheroids. The increment in the diameter/height relation of the nanoparticles gives rise to a succession of topological transformations thatinclude multi-vortex configurations, ferroelectric bubble states, and multi-domain patterns. While the transformation path for flat cylindersis similar to the one previously obtained for cuboids, the thinner edge region of the spheroids prevents the stabilization of one- and twobubblestates. Despite this last difference, our results indicate that the polarization pattern of a nanoparticle depends more on its aspect ratiothan on its shape