| Summary: | 碩士 === 國立臺灣大學 === 應用力學研究所 === 97 === Because ferroelectric materials having many unique features, they have been widely studied and utilized in micro-devices as sensors, actuators and transducers. However, these unique features and behaviors originate from the evolution and arrangement of the underlying microstructures. Therefore, it is essential to investigate the rule of evolution before simulating and taking advantage of these materials. A novel phase-field model for studying and simulating the 2-D domain pattern of ferroelectric materials based on energy arguments is developed in this thesis.
A steady state ferroelectric microstructure is a result as the formation and evolution of microscopic domain patterns in ferroelectrics. This in turn calls for a multivariant framework suitable for microstructure simulation under various boundary conditions to describe the coarsening, refinement, selection, and alignment of microstructure. A different choice of field variables in novel phase-field model, local volume fraction of laminates, is introduced to represent domain configurations by using multirank laminates. As a result, the energy-well structure can be expressed explicitly in a unified fashion. Finally, we observe the domain patterns obtained in simulations by changing the thickness and parameters, and discuss the effect of thickness on compatibility.
The variants in the film problem that our team dealt in the past are periodic and infinite in axials. Considering the effect of free boundary is the main subject this time.
The framework is applied to domain simulation in two-dimensional ferroelectric thin films in tetragonal phase assuming that polarization is close to one of their ground states. The compatible domain patterns obtained in simulations with thick film and are similar to bulk. And then, we compare the computed energy under non-compatible domain with COMSOL to make sure the accuracy.
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