Surface tension assisted polar phases in one-dimensional ferroelectrics


The interest in nanoscale ferroelectric materials has grown significantly in both scientific and industrial fields due to their unique properties, derived from their ability to change their spontaneous polarization. These properties, combined with distinctive dielectric, ferroelastic, and piezoelectric characteristics, open the door to a wide variety of new functionalities and technological applications.

Recent research on nanoscale ferroelectric systems reveals the presence of novel topological excitations, challenging the notion of uniformity in the ground state. These findings raise new questions about the nature of such structures and their potential practical applications, which could be realized by manipulating different topological states.

In this talk, we present a study of free standing PbTiO3 nanowires of different sizes, using an atomistic second-principles approach combined with the Ginzburg-Landau-Devonshire (GLD) model and the phase-field method. The Atomic-level simulations with a core-shell model revealed a strong size effect on the resulting polar textures. This dependency can be attributed to the influence of surface tension, which manifests laterally through the well-known Laplace pressure and longitudinally along the wire axis.

These effects were incorporated into the GLD functional by adding an additional term to the free energy. Using both simulation techniques and analytical calculations, we constructed a radius-temperature phase diagram where the results from the different methods converged.

Two distinct polar phases were identified: the vortex phase, characterized by the rotation of local polarization around the nanowire’s c-axis, and the uniform c-phase, with polarization aligned along the wire axis. In systems with small radii, up to 20 unit cells, the observed polar phase is the vortex phase. However, for larger radii, the low-temperature structure is the c-phase, which transitions to the vortex phase as the temperature increases. At high temperatures, the system becomes paraelectric for all radius values.

The ability to tune their properties makes one-dimensional ferroelectrics valuable in the development of ferroelectric components for advanced devices, such as multi-level logic units or neuromorphic computing circuits. Specifically, the tailored design of nanowires allows for achieving desirable operational properties, ensuring their implementation in nanoelectronic devices.

The seminar will be chaired by Tim Verhagen, Department of Dielectrics.