Preparation And Electrical Properties Studies Of Bismuth Sodium Titanate-based Lead-free Piezoelectric Ceramics

Pizoelectric ceramics is one kind of functional materials,wich can realize the transformation between mechanical energy and electric energy,and could be widely applied to electronic and micro-electronic equipment.The development of lead-free piezoelectric materials is more and more important especially the pollution of lead for the environment.Bi_0.5Na_0.5TiO₃ with better piezoelectric,high Curie temperature and without poison in the preparation,is a promising lead-free piezoelectric ceramic.In this paper,(1-x)Bi_0.5Na_0.5TiO₃-xBaTiO₃lead-free piezoelectric ceramics were perapared by solid state sintering method and learned by preparational technique,design of compositon and solid solution formation.The effects of process conditions on the structure of piezoelectric ceramics (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃(Abbr.BNBT06)were studied by TG/DSC,XRD,SEM and the other analytic methods,and the effects of calcining temperature,sintering temperature and soaking time on the crystalline structure and electrical properties were girven in order to get the most optimization of process condition.The results indicate:the optimization conditions were calcining temperature for 800～850℃,sitering temperature for 1140～1160℃,and soaking time for 2h.BNBT ceramics were investigated with phase transition,microstructure,piezoelectric,and relaxation properties.XRD results show:all the samples were perovsldte structure with relaxation properties.The morphotropic boundary lies in the compositon of 0.06～0.08mol BT content.It has been got the most optimization properties for composition of 0.94BNT-0.06BT and the value of d₃₃,K_p,ε_r,tanδwere 127pC/N,0.22,1388 and 0.05 respectively.In order to improve propterties of piezoelectric ceramics,Li₂CO₃ were added into form solid solution.The results show:all the samples were perovskite structure and Li₂CO₃ added did not destroy the morphotropic boundary of BNBT06 ceramics.The rhombohedral phase decrease as well as the tetragonal phase increase in the morphotropic boundary of BNBT06 ceramic with Li₂CO₃ increased.SEM photos show: all the crystal turns to smaller and the square crystalline boundary changed into round with Li₂CO₃ increased.The dielectric constantε_r increased at fist and then decreased with Li₂CO₃ added.When Li⁺ ions were 0.03mol,the dielectric constantε_r whose value was 1869 got best properties of all the samples.At the same time the dissipation tanδgot the smallest value of 0.04.When the Li⁺ ions were 0.05mol,the piezoelectric properties of ceramic got the best value,wich d₃₃K_p were 160pC/N,0.3 respectively. Though Li₂CO₃ excess,the crystal structure of ceramics were perovskite structure still. The relaxation of ceramics increase but the dielectric constantε_r and piezoelectric constant d₃₃decrease.When the Li⁺ excess was 0.07mol,the piezoelectric properties d₃₃, K_p were 105pC/N,0.1 respectively.In the end,in order to analyse the relaxor behavior of BNT-BT ceramics,we prepared(1-x)BaTiO₃-xBi₍0.5_Na_0.5TiO₃(x=0.05,0.10,0.2,0.3)ceramics by the conventional electric ceramic preparation technique.X-ray diffraction patterns indicate all the Bi_0.5Na_0.5TiO₃ composition doping could be fully incorporated into the pervoskite lattice of BaTiO₃.Compared with pure BaTiO₃ ceramic,the(1-x) BaTiO₃-xBi_0.5Na_0.5TiO₃ ceramics samples show ferroelectfics with diffuse phase transition.It could be got by decreasing dissipation factor,broaden dielectric peaks, increasing curie temperature,improving temperature stability with the Bi_0.5Na_0.5TiO₃ solution.