Research On The Preparation Of KNN Based Piezoelectric Crystal And The Influence Of Doping On KNN

Potassium-sodium niobate has been considered as a most promising candidate for lead-free piezoelectric ceramics.Compared to PZT,KNN based materials generally have high Curied point,but lower dielectric constant and piezoelectric properties.In this paper,the influence of growth method and doping to the KNN properties was studied.K_0.45Na_0.55Ta_xNb_（1-x）O₃-0.004Li Bi O₃series single crystals were prepared by Seed-Free Solid-State Crystals Growth.Grains with grain size ranging up to 100μm were successfully grown on KNN ceramics matrix.XRD analysis showed that the doping amount of Ta could affect the intensity of diffraction peaks of KNN,and the peaks in some directions even disappeared.Through the analysis of dielectric curve and piezoelectric test,the dielectric and piezoelectric properties of the sample were the best when the doping amount of Ta is 0.03.（1-x）K_0.45Na_0.55Ta_0.03Nb_0.97O₃-x Li Bi O₃crystal samples were prepared after selecting the appropriate Ta doping amount.XRD analysis showed that the peak in the（110）direction was strengthened when the doping amount of Li Bi O₃was 0.003.The intensity of the peak was higher and the peak was sharper.According to the results of piezoelectric test and ferroelectric analysis,when the doping amount of Li Bi O₃was0.003,the piezoelectric performance of KNTN was the best and the hysteresis loop was most saturated.On the basis of the experiment of the seed-free solid phase crystal growth,KTaO₃seed crystal was used for the seed crystal solid phase growth.During the sintering process,two kinds of crystal growth behaviors were generated in the KNN ceramic matrix,and the experimental samples were analyzed by XRD,dielectric constant testing,SEM analysis of the ceramic matrix growth single crystal interface,and EDS element analysis.KNTN-0.003LB growth crystal is single crystal with diffraction surface index of（200）and growth direction of<100>.There are two dielectric peaks.The temperature of orthorhombic tetragonal phase transition is about 95℃,and the temperature of ferroelectric paraelectric phase transition is about 434℃.The size of single crystal is centimeter level,and the crystallization rate of ceramic matrix exceeds 2/3.