Construction Of Inhomogeneous Local Structure Of Lead-free Ferroelectric Ceramics And Its Influence On Performanc

Piezoelectric ferroelectric ceramics can realize the conversion between electrical energy and mechanical energy,and its application has been everywhere in People’s Daily life.At present,the traditional piezoelectric ferroelectric ceramics including relaxor ferroelectric ceramics are mostly lead-based ceramics.However,lead-based piezoelectric ferroelectric ceramics would cause damage to the environment and human beings in the process of preparation,use and post-disposal.Lead-free piezoelectric ferroelectric ceramics are considered as promising materials to replace similar lead-based products due to their excellent comprehensive ferrovoltage and electric properties.Therefore,the research and development of lead-free piezoelectric ferroelectric materials has important social and economic value.The design of non-uniform local structure is a very effective method to enhance the properties of lead-free piezoelectric ferroelectric ceramics.The microstructure of piezoelectric ferroelectric materials can be modified at the atomic scale to destroy the long range ferroelectric order,which can enhance the properties of piezoelectric ferroelectric materials and make it breakthroughs.In addition to piezoelectric properties,other electrical properties of piezoelectric ferroelectric ceramics can also be significantly improved by designing non-uniform local structures.Therefore,in this paper,non-uniform local structure is designed and constructed in lead-free piezoelectric ferroelectric ceramics,and the influence mechanism of non-uniform local structure on the performance of lead-free piezoelectric ceramics is systematically studied.The specific research contents and conclusions are as follows:Firstly,the piezoelectric device module in the structural mechanics module of COMSOL Multiphysics was used for the finite element analysis of the 0-3 BaTiO₃composite ceramics with disk-like surface composite ZnO.The ZnO non-uniform local structure with 10μm scale dispersion was constructed in the composite ceramic model,and the piezoelectric stress and polarization were compared with those of pure BT ceramics.The simulation results show that because of the non-uniform local structure of micron ZnO,the performance of the sample is not uniform,but the overall longitudinal piezoelectric constants of the composite ceramics are improved compared with the pure BT ceramics.Then,BT-ZN piezoelectric composite ceramics were fabricated by traditional solid state reaction method and femtosecond laser surface microtreatment.It is found that the enhancement of d₃₃ is due to the contribution of spontaneous polarization.At the interface between BT and ZN,band bending leads to the formation of built-in electric field,and spontaneous polarization is more likely to move.This conclusion has also been verified by COMSOL simulation software.It provides a feasible strategy to improve the piezoelectric properties of piezoelectric ceramics by modulating the band structure of dopants,which is of reference value to the performance optimization of piezoelectric ferroelectric ceramics represented by BT.Based on the above research work,femtosecond laser was used to drill holes on the surface of KNN piezoelectric ceramics,and ZnO,BiFeO₃ and Al₂O₃ submicron powders were filled into the holes to construct the surface 0-3 type non-uniform local structure.The microstructure and electrical properties of KNN-based composite ceramics were systematically studied.The results show that the addition of ZnO and BiFeO₃ enhances the ferroelectric properties of the materials.In addition,the band structures of KNN and three additives were calculated based on DFT.In terms of energy,the improved d₃₃ is derived from similar E_CB and E_VB,which are favorable for self-polarized reorientation and domain switching motion.In summary,we provide a new method for preparing composite ceramics and a new strategy for significantly improving the piezoelectric properties of KNN piezoelectric ceramics by adjusting the band structure of additives.Finally,the piezoelectric ferroelectric ceramics with multiferroic properties that can realize magnetoelectric coupling function are controlled by the construction and design of non-uniform local structure and the interface effect caused by it.Magnetoelectric coupling of multiferroic heterojunction in KNN piezoelectric ceramics was realized by solution coating synthesis.The remanent magnetization（M_r～0.043 emu/g）and remanent polarization（P_r=8.12μC/cm²）of 0.8KNN-0.2Fe₂O₃ceramics were obtained simultaneously.M_r And P_r of BiFeO₃ perovskite ceramics prepared by one-step solid state reaction method are higher than those of BiFeO₃perovskite ceramics prepared by one-step solid state reaction method.TEM analysis shows that（1-x）KNN-xFe₂O₃ heterojunction structure exists in KNN-based ceramics.Combined with COMSOL simulation,this multiferroic heterojunction structure is the main reason for improving the ferromagnetic properties of kn N-based ceramics.In addition,KNN-Fe₂O₃ ceramics have high piezoelectric constants(d₃₃=80 pC/N～115pC/N).The magnetoelectric coupling effect of 0.8KNN-0.2Fe₂O₃ ceramics can be used to expand the function of devices and meet the requirements of miniaturization of electronic components.