Study On Preparation Of High Performance Potassium Sodium Niobate Piezoelectric Single Crystal By Solid-State Growth Method

Preparation of piezoelectric single crystal is an important method to improve the piezoelectric properties of piezoelectric materials,in which the solid-state crystal growth method is a simple,low cost,single crystal preparation method with excellent performance,and can avoid serious component segregation.However,it is difficult to prepare large-size K_0.5Na_0.5Nb O₃（KNN）piezoelectric single crystal by solid-state crystal growth method,mainly because of the slow growth of{100}crystal surface of KNN.In recent years,researchers have prepared several centimeters of KNN-based piezoelectric monocrystals by seedless solid-state crystal growth method,However,it is difficult to control the orientation and size of the grown crystals.In order to be able to use the solid-state crystal growth method to prepare the orientation and size controllable KNN-based single crystal with large size at the same time,In this paper,the advantages of seeded and seedless solid-state crystal growth method for preparing KNN single crystal are combined.On the basis of K_0.5Na_0.5Nb O₃-0.4mol%Li Bi O₂ which can grow single crystal through seedless crys-tal,xmol%Li₂CO₃ was added as liquid phase sintering assistant.It is found that when x=2 and x=3,crystal growth size increases significantly,indicating that appropriate liquid content can promote the growth of single crystal.Then,on the basis of x=2,<110>KTa O₃ seed crystal was added to grow KNN-based single crystal directionally.By controlling the sintering temperature,the single crystal with size of 13 mm*9mm*2 mm was obtained under the condition of only 10 h sintering time.The test of dielectric temperature spectrum shows that Curie temperature T_C=428℃for single crystal,orthorhombic-tetragonal phase transition temperature T_O-T=92℃,and the di-electric loss is less than 0.6%ranging from room temperature to Curie tempera-ture.The residual polarization intensity of single crystal Pr=15.0μC/cm² and coer-civity field is 14.7 k V/cm.When the electric field intensity is greater than 20 k V/cm,the leakage phenomenon of electric hysteresis loop is obvious.When the polarization temperature is 60℃and the polarization electric field intensity is 20 k V/cm,the pie-zoelectric constant d₃₃ is 200.8 p C/N.Scanning electron microscopy（SEM）images of the interface between single crystal and ceramics show that the crystal grows in a faceted manner,and the faceted crystal grows in a two-dimensional nucleation mode.In this experiment,large single crystal is successfully grown by mixed control theory of two-dimensional nuclea-tion.This study also provides important reference value for the preparation of other crystals with faceted plane growth mode by solid state crystal growth method.