Research On The Flexoelectricity From The Crumpling Of Dielectric Films

Non-uniform deformation of the dielectric subjected to external forces can induce the electrical response,i.e.,flexoelectricity.The flexoelectric effect exists in all dielectric materials and is size-dependent.It has been reported that by reducing the sample size and increasing the strain gradient,the electromechanical coupling of the dielectrics can be significantly improved.For 2D materials such as thin films,large curvatures,i.e.,strain gradients,is easily generated.Then,for thin dielectric films,a strong flexoelectric response can be easily generated due to the coupling between strain gradients and polarization.This property of dielectric films makes them an important vehicle for flexoelectric applications.In this thesis,we take the crumpling dielectric film as the basic research object,and to further enhance the flexoelectric response of the crumpling dielectric film,we adopt the design ideas of functional gradient materials and laminated structures,respectively,to optimize the design of the dielectric film.For the functional gradient dielectric films,the theoretical model of electromechanical coupling of crumpling functional gradient dielectric films is established in this thesis.Young’s modulus,thickness and flexoelectric coefficient of the films are used as design parameters.respectively,to study and analyze the overall mechanical properties of the functional gradient dielectric films and the flexoelectric response when the crumpling deformation occurs.The results show that for dielectric films with gradient thickness,if the film thickness increases linearly along the radius direction,the film reaches the maximum flexoelectric energy efficiency with an overall size twice that of the uniform film and a maximum flexoelectric energy efficiency five times that of the uniform film.For dielectric films with gradient Young’s modulus,Young’s modulus of the film increases linearly along the radius direction,and the overall size of the film is the same as the uniform film when the film reaches the maximum flexoelectric energy efficiency,and the maximum flexoelectric energy efficiency is 2.5 times that of the uniform film.For dielectric film with gradient flexoelectric coefficient,flexoelectric coefficient of the film decreases linearly along the radius direction,and the film reaches the maximum flexoelectric energy efficiency with an overall size 0.65 times that of the uniform film and a maximum flexoelectric energy efficiency 3.5 times that of the uniform film.For the laminated dielectric film,this thesis takes the three-layer laminated dielectric film with same edge layers as the research object,investigates the crumpling problem of the laminated dielectric film,establishes the theoretical electromechanical model of the crumpling laminated dielectric film,takes the ratio of thickness of the middle layer and the edge layers and the ratio of Young’s modulus as the control parameters,respectively,and investigates and analyzes the overall mechanical properties of the crumping laminated dielectric film and the energy efficiency of flexoelectricity of the dielectric film.The results show that when Young’s modulus of the middle layer or the edge layer is constant,the reduction of Young’s modulus of the other layers can improve the energy efficiency of flexoelectricity of the laminated dielectric films.Moreover,the reduction of Young’s modulus of edge layers can improve the flexoelectric effect more significantly.Meanwhile,increasing the thickness of layers with reduced Young’s modulus will further enhance the flexoelectric response of the laminated films.The maximum value of flexoelectric energy efficiency that can be achieved by laminated films is one order larger than that of uniform films.At this point,the size of laminated films is 3 times larger than that of uniform films.