| Summary: | 碩士 === 國立臺灣大學 === 應用力學研究所 === 96 === Ferroelectric materials exhibit spontaneous polarization and distortion under the transformation temperature, giving rise to very characteristic microstructures. The arrangement and evolution of microstructures can induce significant nonlinear behaviors, so they are widely used as smart materials. As ferroelectric microstructures are the key to achieving the exceptional properties, it is essential to investigate the mechanism that governs their formation and evolution.
In this thesis, we study the prescribed issue by developing a non-conventional phase-field model. It is based on energy arguments where competing energetics are used to describe the coarsening, refinement, selection, and alignment of ferroelectric domains. In addition to the conventional use of polarization as order parameters, we adopt a new set of field variables motivated by multirank laminates to characterize energy-minimizing domain configurations. As a result, the energy-well structure can be expressed explicitly in a unified fashion, and the number of input parameters in the present framework is reduced.
This model is applied to domain simulation in both the tetragonal and rhombohedral ferroelectrics. Several electromechanical self-accommodation patterns are obtained in the simulations and found in good agreement with experimental observations. Besides, rearrangements of domains under applied electric field along polar/non-polar directions are investigated. Preliminary result of hysteretic behavior is also presented. Finally, parameter study is also conducted to verify the model.
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