Research On Nonlinear Hysteresis And Domain-switching Dynamics Of Ferroelectric Devices

Electro-mechanical devices based on linear piezoelectric effect cannot meet the ever-increasing industrial demand due to some intrinsic limits,such as insufficient energy transferring efficiency,narrow operating bandwidth,limited actuation strain and et.al.Due to the novel energy transferring mechanism relying on polarization switching,ferroelectric devices provide a different and promising choice.However,the involved complicated nonlinear hysteresis and domain-switching dynamics make it very difficult to design,optimize and control these ferroelectric devices.With the financial support from National Science Foundation project(NO.51575478):research on ferroelectric acoustic dissipation based on polarization switching,a series of work about nonlinear hysteresis and domain-switching dynamics of ferroelectric devices has been conducted and provided in this dissertation,which includes:Based on multiscale investigation and modeling of the underline polarization switching,a novel differential operator-based hysteresis model has been constructed.In the microscopic level,a differential operator is constructed based on Landau phenomenological theory and general Lagragian mechanics.The dynamic hysteretic polarization switching is well captured by the differential operator.In the macroscopic level,the coercive field and interaction field are assumed to be distributed and a density function is constructed to characterize the distribution.Thus,material hysteresis is modeled by weighted summation of different operators just as in the classical Preisach model.In addition,numerical implementation method,parameter estimation strategy and numerical inversion algorithm for the proposed model have been carefully discussed.Furthermore,the differential operator-based hysteresis model has been extended for modeling the magnetic hysteresis considering the similarity between these two phenomena.In the original version of the differential operator-based model,only 1800 polarization switching is considered and stress-dependent ferroelectric hysteresis cannot be captured.For this reason,the extension of the differential operator-based model is further carried out.In the microscopic level,the free energy is extended to include stress-related terms.In the macroscopic level,the idea of 'redistribution of the density function' is proposed.Numerical experiments demonstrate that the extended model can well capture the ferroelectric hysteresis under different bias stress levels.To tackle the robust deficiency problem associated with existing ferroelectric nanogenerators,which largely rely on the topological stability of the domain structures,an improving method has been proposed.With the proposal of a novel energy harvesting circuit,a bias electric field is introduced,stress-induced polarization switching is repeatable,and input mechanical energy can be continuously converted to useful electricity.The influence of bias voltage,bias resistance and leakage current on the energy harvesting performance of the improved ferroelectric nanogenerator has been carefully investigated via phase field method.Besides,energy flow chart for the ferroelectric energy harvesting system has been constructed for the first time.With a careful comparison with the piezoelectric nanogenerator,an extremely high energy output has been demonstrated.Within the framework of continuum mechanics,a thermo-electro-mechanically coupled ferroelectric phase field model has been proposed,and the effect of temperature field has been included.Based on the fully-coupled phase field simulation of the domain-switching dynamics,temperature management problem of nanoscale ferroelectric actuator has been carefully discussed.Heat production details and mechanism involved in typical working cycles have been demonstrated.Besides,the influence of actuation frequency and thermal boundary condition on heat production of these devices has been investigated via the phase field simulation.Finally,strategy for temperature management of these devises has been constructed based on the investigation.