Study On Preparation And Properties Of Potassium Sodium Niobate-based Ceramic Materials

Lead-based ceramic systems in the field of piezoelectric ceramics are widely used in fields such as transducers,resonators,and speakers.However,lead-based system products will inevitably produce lead oxide that is extremely harmful to humans and the environment during the preparation and subsequent use.Therefore,many countries have issued a series of laws and regulations to restrict the application of lead-containing systems.(K_0.5Na_0.5)Nb O₃（KNN）-based ceramics is an environmentally friendly ferroelectric structure of ABO₃ perovskite,which has been widely studied by scholars and researchers in various countries for its excellent ferroelectric,piezoelectric and dielectric properties.However,because the alkali metals K⁺and Na⁺are extremely volatile when sintered at high temperatures,the ceramics prepared often deviate from the design composition,and it is difficult to prepare high-density and high-performance ceramics by means of atmospheric sintering.In this paper,the effects of different oxide doped ions on the structure,morphology,ferroelectric,piezoelectric,dielectric,luminescence and impedance properties of KNN based ceramics were systematically studied.First,the solid-phase reaction method was used to prepare the（1-x）Na_0.5K_0.5Nb O₃-x Li Sb O₃ ceramics introduced with Dy³⁺,and the structure,morphology,electrical properties,fluorescence properties,and defect chemistry near the PPT region of the ceramic system were systematically studied.It is found that the orthogonal（orthorhombic,O）and tetragonal（T）phases coexist in the ceramic sample with component x=0.04,and the current component shows the best performance:P_r=32.2 C/cm²,E_c=12.26 k V/cm,T_c=325 ^oC,tanδ≤1.5%（250～400 ^oC）.With the advantage of fast response of Raman spectroscopy and PL spectroscopy,the phase transition near the PPT region in NKN-x LS:0.006Dy³⁺ceramics can be well measured.This chapter provides an effective method to study the phase transition of KNN ceramics.Second,the crystal structure,dielectric properties,impedance properties and relaxation behavior of（1-x）KNLNTS-x BT ceramics were studied.The phase structure of ceramics changed from O phase（0.00≤x≤0.02）to O-T two-phase coexistence structure（0.02<x<0.06）,and finally changed to T phase（0.06≤x≤0.10）.With the help of Curie-Weiss and modified Curie-Weiss law for dielectric performance analysis,as the content of barium titanate increases,the degree of relaxation of（1-x）KNLNTS-x BT ceramics increases,exhibiting excellent relaxation characteristics.For the sample of component x=0.10,the diffusion coefficientγreached the maximum value of 1.73.According to the impedance spectrum changes with temperature,relaxation and conduction behavior are related to thermal activation,and oxygen vacancy is a potential ion carrier.In addition,the activation energy of component x=0.10 ceramics was 0.82（6）e V by Arrhenius fitting.According to the change of impedance spectrum with temperature,relaxation and conduction behavior are related to thermal activation.And oxygen vacancies are potential ion carriers.In addition,by Arrhenius fitting,the activation energy of the component x=0.10 ceramic is 0.82（6）e V.Third,by synthesizing KNLNTS:x Eu ceramics,the effects of Eu₂O₃ on the crystal structure,microstructure,dielectric properties,and luminescence properties before and after polarization were studied.It was found that the KNLNTS:x Eu ceramics with proper amount of Eu³⁺can obtain the pure phase perovskite structure.However,the tetragonality of ceramics is weakened,and the crystal symmetry of ceramics is enhanced and close to the cubic phase.By increasing the content of Eu³⁺,dense KNLNTS:x Eu ceramics can be obtained,which will reduce the Curie temperature of the ceramics and the phase transition temperature of the orthogonal-tetragonal phase.Through the modulation effect of ferroelectric polarization on the luminescence intensity,it was found that the polarization would reduce the fluorescence emission intensity of the samples.Rational use of polarization modulation of multifunctional luminescent ferroelectric materials is of great significance for the development of display field.