Phase field model

Phase field model

Ferroelectric materials possess a spontaneous polarization in unit cells, which can be reoriented by applying an electric field or through mechanical forces. At the nanoscale, the polarized unit cells group together to form polarization patterns (microstructures) that determine ferroelectric properties. Using a phase-field model, I predict how a polarization pattern evolves and responds to external loads. The results are applied to design ferroelectric nano-actuators and energy harvesters. Furthermore, the results motivate research towards developing prospective nanoscale applications from other smart materials, such as relaxors and ferromagnets.

Below are some examples of actuation cycles simulated using phase-field methods. In these videos, you’ll see the polarization pattern evolving in the ferroelectric material on the left-side of the frame. The corresponding actuation strains are plotted on the right-side of the frame.

Example 1 – Embedded nanoactuator

Example 2 – Bending nanoactuator

Here is a brief explanation of how the actuators work:

I use the phase-field model as a design tool to develop ferroelectric energy harvesters and memory elements. The results from the simulations assist in developing device prototypes and eventually benefit industrial fabrication. Furthermore, I use the phase-field model to test the stability of laminate patterns in ferroelectrics.

The figure above illustrates the stability of in-plane polarized laminate patterns under zero external loads. While the herringbone laminate patterns in subfigure (a) is stable at equilibrium, the other complex laminates (b-c) dissolve to form simpler polarization patterns at equilibrium. In this paper, I stabilized the laminate patterns by applying mechanical stresses and electric fields. These results explain prior experimental observations of polarization patterns and provide useful insights on how to engineer domain configurations for nanoscale ferroelectric applications.

Collaborators: John Huber University of Oxford, UK
                           Ingo Muench Karlsruhe Insitute of Technology, Germany
                           Chad Landis University of Texas at Austin, USA

Related references
Nanoactuators Energy harvester LaminatesVortex pattern

Note pdfs (preprints) of these papers are available for educational purposes on the publications page