Fabrication And Research On Lead-free Capacitor Ceramics

Capacitor ceramics are widely used nowadays. The traditional lead-baseddielectric ceramics, which do harm to the environments and the health of human being,can't meet the demands any more when people attach more and more importance tothe environments. The scientists of materials all over the world have aimed atdevising a new, nonpolluting, high properties, and lead-free dielectric ceramics. Barium titanate and bismuth sodium titanate are investigated in the content. Weoptimize the dielectric properties to meet the demands for practice applications bydoping. Ce (CeCl3 and CeO2 0~20at%) and CuO (0~8wt%) are used in barium titanateto lower the sintering temperature and restrain the temperature-variability in dielectricproperties; Y2O3 (0~1.0at%)is used in bismuth sodium titanate to enhance thedielectric properties. Barium titanate and bismuth sodium titanate have the samestructures (perovskite) and close components, so the composition dependence ofdielectric properties of barium titanate and bismuth sodium titanate system (BaTiO30~16at%) is studied, Y2O3 (0~1.0at%) and CeO2 (0~1.0at%) doping are performed. Well-sintered sample in various composition are obtained at different sinteringtemperature. Two component of them stand out as optimum properties samples. 1).BaTiO3 sample (CeO2 7at%, CuO 0.5wt%) sintered at 1260℃ for 2h: εr=2590,tgδ=2.15%, ρ=5.8×107?·cm; xBaTiO3- (1-x)(Bi0.5Na0.5) TiO3 (x=0.06, CeO2 0.5at%)sintered at 1160℃ for 2h: εr=1620, tgδ=1.80%, ρ=4.84×107?·cm. The results of experiments shows: Ce4+ ions enter the B-site of perovskite (ABO3)in BaTiO3 ceramics, so the domain structure changes which lead to Tc-shifting to theroom temperature, thus the dielectric properties are improved; CuO brings liquidphase in high temperature environments, which can accelerate matter transfer, thus itlead to a lower sintering temperature, higher resistance and density of the sinter. Thecombining of xBaTiO3- (1-x)(Bi0.5Na0.5) TiO3 can produce ion vacancies and spacecharges, which can loose the domain structure and restrain the charge transfer, so thedielectric properties is enhanced. CeO2 doping in 0.06BaTiO3-0.94(Bi0.5Na0.5) TiO3can lower tgδ further and widen the curie peak. The phase transformation process of(Bi0.5Na0.5) TiO3 based ceramic is analyzed according to the pattern of temperaturedependence of dielectric properties. A new opinion about the phase transformationprocess in high temperature environments is concluded in the content.