Study On (Bi_0.5Na_0.5)TiO₃-BaTiO₃ Systems For Lead-Free Piezoelectric Ceramics

Since environmental issues are world-wide and concern every human activityfundamental improvements in the materials being used are needed to safeguard thenatural environment.Lead-free piezoelectric ceramics thus attract more and moreinterest.There has been evidence showing (Bi0.5Na0.5)TiO3-BaTiO3(Abbr.BNBT)ceramics could be excellent candidate as lead-free piezoelectric ceramics.Here,BNBT ceramics were prepared by solid-state conventional ceramicpreparation method.For (1-x)Bi0.5Na0.5TiO3-xBaTiO3(x=0.02,0.04,0.06,0.08,0.10 ) lead-free ceramics system , the piezoelectric dielectric properties ,microstructures,relaxation property and phase transition were investigated with ourexperimental conditions.XRD results show that all of samples have mono-perovskitestructure,and in the compositions we studied they are all ferroelectric relaxors.XRDand HRTEM results show that the morphotropic lies in the composition of x=0.06.The effects of process conditions on the structure of ferroelecttric ceramics(Bi0.5Na0.5)0.94Ba0.06TiO3 (Abbr. BNBT-6) were studied by DSC/TG,XRD,SEM and other analytic methods,and the effects of sintering temperature and soakingtime on the crystalline structure were given.In order to determine the reasonabletechnological parameters ,the piezoelectric dielectric properties dependence ofcalcining condition,sintering temperature,maintaining time and calefactive velocitywere studied.The results show that the reasonable calcining condition is at 800℃~850℃,and sintering temperature and soaking time limit and complementarity eachother.A high sintering temperature is needed by a short maintaining time and vicevisa.If soaking time is 2h,1140℃~1160℃ is the proper range of sinteringtemperature.We studied on the dielectric properties of BNBT samples from room temperatureto 400℃ at 1kHz ,and the dielectric properties of BNBT-6 sample from roomtemperature to 400℃ at different frequencies(1kHz, 10kHz,100kHz). IIThe crystal structure including phases,boundaries of grains and domains wasinvestigated by using high-resolution transmission electron microscope(HRTEM).According to HRTEMI and SAEDP of BNBT-6,ordered and disorderedstructures were found. The results show that BNBT-6 has a pseudocubic structure,and the domains can clearly be seen formed by rhombohedra and tetrahedra.Anordered model that a pseudocubic on A-site was proposed and simulated.In present,there is no literature reports about these studies whatever at home or abroad.