Study On Ceramic Injection Molding Preparation And Electrical Properties Of BNT-BT Lead-free Piezoelectric Ceramics

Piezoelectric ceramics are widely used in sensors,transducers and energy storage equipment,and are important new materials with high technology.Traditional piezoelectric ceramics contain lead,which can easily cause harm and pollution to human body and environment.In order to meet the requirements of environmental coordinated development,the development of lead-free piezoelectric materials with high performance has become an urgent technical problem.This paper takes bismuth sodium titanate-barium titanate(abbreviated as BNT-BT)lead-free piezoelectric ceramics as the research object.On the basis of template grain growth technology(abbreviated as TGG),the ceramic billet is prepared by ceramic injection molding(abbreviated as CIM)technology for the first time,and lead-free piezoelectric ceramics are prepared by BNT-BT applied electric field,thus improving the piezoelectric properties of ceramics.This research is of reference value and theoretical significance for the development of lead-free piezoelectric ceramics with better performance.The main research contents and results are as follows:(1)A two-step molten salt method was used to prepare BT template grains.The effect of molten salt content and sintering temperature on the physical phase structure and microstructure of BT grains was studied.The effect of molten salt content and sintering temperature on the physical phase structure and microstructure of BT grains was studied.The results show that too high or too low molten salt content will affect grain development and growth.BT grains with single phase structure and excellent microstructure can be obtained when the molten salt content is 1:1.If the temperature is too high,the BT template powder will produce rod-like grains.When the temperature is too low,it will lead to incomplete grain development and large size difference.It is found that the growth of sheet BT template particles in molten salt is a process of dissolution and recrystallization.The addition of excess Ba2+ makes the precursor Ba4Ti13O30 decomposed,which further reacts to grow into BT template grains.The ideal preparation conditions are as follows:the mass ratio of molten salt to reactant is 1:1 with NaCl as molten salt,the synthesis temperature is 1050?,and the holding time is 3 h.(2)Lead-free piezoelectric ceramics BNT-BT prepared by TGG method.he physical phase,microstructure and piezoelectric and dielectric properties of ceramics in the Morphotropic Phase Boundary(MPB)region by sintering process were studied.The results showed that the phase structure of BNT-BT was not changed by the changes of pre-sintering temperature,sintering temperature and holding time,but the proportion of tetragonal phase in BNT-BT ceramics increased with the increase of pre-sintering temperature and sintering temperature,and the content of tetragonal phase gradually decreased with the extension of holding time.In addition,with the increase of sintering temperature and holding time,the piezoelectric and dielectric constants of ceramic samples show the trend of first increasing and then decreasing.The densification of ceramics increased gradually at pre-burning temperature of 700??900?,and the piezoelectric and dielectric constants increased.changes in temperature and holding time did not significantly change the characteristics of BNT-BT ceramic dispersion relaxation ferroelectrics.Therefore,for BNT-BT ceramics,when the pre-firing temperature is 900?,the sintering temperature is 1150?,and the holding time is 2?4 h,it has the optimal comprehensive performance:d33=113 pC/N,kp=0.221,?r=831,tan?=0.0255,density ?=5.83 g/cm3(3)The lead-free piezoelectric ceramics of BNT-BT were prepared based on the TGG method.the ceramic billet was prepared by using CIM technology.The effects of injection temperature and injection pressure on the quality and electrical properties of the ceramic billet were studied to determine the optimal injection conditions.The orientation degree of BNT-BT ceramics is expected to be improved by CIM technology,and then the piezoelectric properties of ceramics are improved.According to the research,the increase of injection temperature and injection pressure can effectively improve the surface quality of ceramic billet and improve the coMPactness of ceramics,but it has little effect on the orientation degree of ceramics in the(001)direction.With the increase of injection temperature and injection pressure,the piezoelectric constant d33 and dielectric constant ?r both increase first and then decrease,and the dielectric loss tan? remain low at this time.(4)Preparation of 0.94 BNT-0.06BT lead-free piezoelectric ceramics based on CIM technology,electric field was introduced during injection to study the effect of electric field strength on the electrical properties of ceramics.As the electric field intensity increases,the d33 increases.With the increase of electric field intensity at the same frequency,the ?r increases continuously tan? the stable state is maintained.All ceramic samples have high curie temperatures(Tc=299??324?).The mesothermal curves of the samples at 0?5 KV/mm electric field intensity show that the samples exhibit relaxation dispersion phase transition characteristics.It is found that applying electric field can improve the electrical properties of ceramic system.It is found that applying electric field can improve the electrical properties of ceramic system.when the electric field intensity is 5 KV/mm,the ceramic sample has the best piezoelectric properties:d33=156 pC/N,kp=22.04%.