Phase-Field Simulation On Domain Structure Evolution Dynamics And Electromechanical Manipulation In Nanoscale Ferroelectric Materials

With the rapid development of MEMS and other related fields,electronic products face the challenge of miniaturization and high integration.Ferroelectric material is a new type of functional material,which can maintain its own physical properties at a very small size and at the same time has multi-physical field coupling characteristics.With the deepening of the research,ferroelectric materials gradually become a research hotspot in the field of functional devices.Ferroelectric domain structure is a unique microstructure of ferroelectric materials.In low-dimensional material systems,ferroelectric materials exhibit rich topological domain structures due to the competition among various internal energies.Numerous unusual topological domain structures,such as polar vortex arrays,bubble domains,and skyrmions,have recently been found in low-dimensional ferroelectric systems as a result of scholars’ ongoing and thorough study.Compared with others,vortex domain structure shows great application prospects in the fields of high-density non-volatile storage because of its exceptional topological protection mechanism and tiny size.The chiral control strategy of vortex domains has become a research hotspot in the area of condensed matter physics.Currently,the vortex domain is primarily manipulated by external electrical fields.But the application of external electric field on ferroelectric materials needs extremely high voltages.Cyclic loading can easily lead to electrical exhaustion and impact material characteristics.Mechanical manipulation is thought to possess wealthy research potential because ferroelectric materials typically have good piezoelectric properties.This article investigates the domain structure evolution and manipulation in various low-dimensional ferroelectric systems,which is dependent on thermodynamic theory.We try to propose effective control strategies in terms of electricity and mechanics methods about their physical manipulation.Then,the novel physical mechanism within ferroelectric materials is explored.The specific research content of the article is arranged as follows:(1)In the introduction,firstly,we provide a brief overview of ferroelectric materials which has more than 100-year history since they were proposed.Subsequently,research results in recent years on the physical regulation strategy of the topological domain structure are investigated in detail.In the second chapter,starting with the ferroelectric thermodynamic theory,a phase field simulation method on low-dimension ferroelectric materials is established combing with Landau-Ginzburg phase transition theory and ferroelectric multi-field coupling effect.(2)In the third chapter,the evolution of domain structures in lead titanate nanodots is studied.We proposed a charge screening model in this chapter and research its effect on the microstructure evolution.The findings demonstrate that the charge screening effect can manipulate the ferroelectric system’s symmetry allowing chirality to be modified by a uniform electric field.In addition,the vortex domain switching process is significantly influenced by both temperature and charge screening effect.(3)The fourth chapter investigates the impact of the charge screening effect on the microstructure evolution of the lead zirconate titanate film.The temperature-misfit strain phase diagram of thin film is then sketched in accordance with the calculation results.During the investigation,a brand-new ferroelectric failure mechanism is discovered.The results imply that the vortex domain structure may be destroyed by the depolarization field.This phenomenon complements the vortex domain formation mechanism which is dominated by the depolarization field.In addition,we also study the influence of charge screening effect and size effect on the depolarization field,and proposed the scope of their influence on ferroelectric materials according to the calculation results.(4)In the fifth chapter,we study the domain structure in lead zirconate titanate nanodisk and propose the temperature-misfit strain phase diagram according to the calculation results.We discovered a vortex domain structure with central polarity in this system under certain misfit strains.The phase diagram demonstrates that the geometric dimension has a significant impact on the evolution result of the domain structure.We propose a control strategy for switching the polarity of vortex domains by applying an axial electric field.Then we studied the influence of size effect and composition ratio on the polarity of vortex domains.The calculation results show that the polarity in the vortex domains will gradually disappear with the increase of the diameter and proportion of titanium ion.(5)In the sixth chapter,a mechanical loading model is proposed based on continuum mechanics and small deformation theory.The precise control of the polarity of the vortex domains is achieved by applying a torsional load on the surface of the nanodisk.The calculation results show that a skyrmions-like topological domain structure can be induced by torsional loading in this system.At the same time,we utilize the pinning effect of the torsional load on the out-of-plane polarization to propose a synergy control strategy that combines the torsional mechanical loading and the axial electric field.This switching method can precisely control the polarity and vorticity of vortex domain.These research results have reference significance for the design of subsequent mechanical control experiments and the discovery of new topological structures.