Preparation And Research Of NBT-BT Binary System Ceramic Capacitor Material

Sodium bismuth titanate,Na_0.5Bi_0.5TiO₃(NBT),is a kind of perovskite-type relaxation ferroelectric with a relatively high Curie temperature(T_c=320℃) and strong ferroelectrics at room temperature.For its clear relaxation in the dielectric temperature peaks,NBT has good temperature stability.Barium titanate has been widely used in preparing ceramic capacitors for its excellent dielectric constant.However,as a result of the dielectric constant change rapidly at Curie temperature(T_c=120℃),causing capacitance mutations and effecting the stability of the circuit.In order to improve the dielectric property,in this paper,compounding NBT and Barium titanate to become NBT-BT binary system ceramic to attain the capacitor materials with good dielectric temperature characteristics.In this dissertation,a conventional ceramic fabrication method-Solid phase synthesis was employed to prepare the(1-x)(Na_0.5Bi_0.5)TiO₃-xBaTiO₃ ceramic with different BaTiO₃ contents(x),using Na₂CO₃,TiO₂,Bi₂O₃ and BaTiO₃ as the raw materials.The composition, microstructure,characteristics and electric properties were tested by XRD,SEM,LCR.The relations between different materials preparation(such as the pre-sintering temperature and the sintering temperature) and the structure,dielectric properties were also investigated. Analysizing the contact of NBT ceramic materials dielectric properties,components and structure.The results show that,the synthesized temperature of NBT-BT powder increased as the increasing of BaTiO₃ amount.The optimum calcined temperature is 850℃with x＜0.06, 900℃with x=0.06 and 950℃or more than 950℃with x＞0.06.It is resulted that the sintering temperature range was narrow.Moreover,particle size of the ceramic samples decreased and the dielectric constant increased with the increasing of BaTiO₃ content.The particle size of(Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃ which was pre-sintered at 900℃and sintered at 1170℃for 2h is only 1μm.Besides,it has the best dielectric properties.Under 1kHz test conditions and at temperature from 0℃to 100℃,the dielectric constants(ε) of this sample has a value of 1700～2000,with low temperature coefficient capacitance of 2%and flat relationship curve between temperature and dieleectric dielectric constants.In addition,the dielectric loss value tanδis only 5.0%to 5.5%.