Study On Doping Modification Of Potassium Sodium Niobate Based Ceramics

With the continuous development of society,lead-free and multi-functional piezoelectric materials have become the trend of the times.As a kind of functional ceramics,potassium sodium niobate(K_1-xNa_xNbO₃,abbreviated as KNN)piezoelectric ceramics have been widely paid attention due to their excellent piezoelectric properties,high Curie temperature and high electromechanical coupling coefficient.In recent years,a series of piezoelectrical KNN based ceramics,photoelectric multifunctional KNN based ceramics or KNN based energy storage ceramics have been prepared by doping methods.In this paper,a series of KNN based ceramics were prepared by using the traditional solid-phase synthesis method and different ion doping,crystal structure,microstructure and photoelectric properties of the doped ceramics were analyzed.The main research contents are as follows:1.Pr and Sm doped KNN ceramic samples were prepared by the traditional solid-state reaction method.The results show that all the ceramics have pure perovskite structure,and the phase structure changes from orthorhombic phase to pseudo-cubic phase at room temperature.After doping rare earth elements,the grain growth is inhibited and the grain size decreases obviously.After entering the KNN lattice,rare earth ions occupy A site,resulting new A site vacancy,showing“soft”doping characteristic,and leading to the increasing dielectric constant at room temperature.Through the PL spectrum,it is found that under the 463 nm excitation,KNN ceramics co-doped with Pr and Sm show orange emission.2.Sr₂MnSbO₆（SMS）doped KNN ceramic samples were prepared by the traditional solid-state reaction method.The results show that there are no impurity peaks appear after doping SMS,and a single perovskite structure is formed.1mol%SMS can effectively improve densification and piezoelectric performance.Higher doping levels will reduce the grain size and reduce the electrical properties.The sample with SMS content x=2 exhibits diffusion phase transition behavior.Besides,after doping 1 mol%SMS,the unipolar strain and the remnant polarization vary less than undoped KNN ceramics in the temperature range of 30-160℃.Therefore,doping SMS is an effective way of increaseing the temperature stability and electrical performance of KNN piezoelectric materials.3.The（0.9985-x）(K_0.49Na_0.49Li_0.02)(Nb_0.8Ta_0.2)O₃-0.0015Ho₂O₃-xmol%CaZrO₃（KNLNT-Ho-x CZ）ceramics were prepared by the traditional solid-state reaction method.The results show that all ceramic samples have a single perovskite structure with no visible impurity phase.The grain size decreases with the increase of CaZrO₃content.Strong green emission（～551 nm）is observed at 453 nm.In addition,Rayleigh analysis show that doping CaZrO₃can reduce grain size,make domain wall movement and domain inversion difficult,thus weaken the external contribution of the ceramics.4.The0.96(K_0.48Na_0.52)(Nb_0.97Ta_0.03)O₃-（0.04-x）Bi(Zn_0.5Ti_0.5)-x Nd₂O₃（KNNT-BZT-x Nd）ceramics were prepared by the traditional solid-state reaction method.The results show that all ceramics are pseudo-cubic structures at room temperature.The relaxor-like behavior of the ceramics is induced by the addition of Nd,and the grain size decreases with the increase of doping amount.Through hysteresis loop（P-E）analysis,it is seen that better energy storage performance is obtained at 160kV/cm for the x=0.002sample:effective energy storage density W_rec=1.09 J/cm³,and energy storage efficiencyη=50%.Through the charge-discharge performance test,it is found that KNNT-BZT-0.002Nd ceramics has a higher discharge energy density W_d=0.79 J/cm³and faster charge-discharge time t_0.9=54 ns.