Microstructure And Electrical Properties Of BT-BKT-base Lead-free PTC Ceramics After Doping Modification

Ba TiO₃-K_0.5Bi_0.5TiO₃?abbreviated as BT-BKT?based lead-free PTC ceramic is a high-temperature ceramic,which is substituted by A and B-site ion on BaTiO₃ based ceramic.In this thesis,BaTiO₃-K_0.5Bi_0.5TiO₃-base lead-free PTC ceramic was successfully prepared by conventional solid-state sintering technique to obtain the superior electrical properties.The influence of Nb₂O₅,SnO₂,CuO dopant on phase structure,microstructure,HR-TEM and electrical properties of BT-BKT-base lead-free PTC ceramics were investigated.The main conclusions are as follows,?1?The influence of the BKT doping on microstructure,phase composition,electric properties and of the?1-x?BaTiO_3-xK_0.5Bi_0.5TiO₃?x=0.02,0.04,0.06,0.08mol??abbreviated as?1-x?BT-x BKT?were investigated.The experimental results show that all samples posses a pure perovskite structure.When the content of BKT increases,BKT inhibit grain growth,so that the grain is refined.?1-x?BT-xBKT ceramic obtains the excellent properties when x=0.004 mol,?RT = 130.3 ?·cm,lg??max/?min?= 3.165;?2?The influence of the Nb₂O₅ doping on the microstructure,phase composition,electric properties of(Ba_0.96Bi_0.02K_0.02)TiO_3-xNb?x=0.05%,0.1%,0.15%,0.2% mol??abbreviated as BT-BKT-xNb?were investigated.The results indicate that all the samples emerge a pure perovskite phase structure diffraction peak.When the content of Nb₂O₅ increases,the grain size becomes smaller and relatively homogeneous,and the dopant has a critical value.The results of dielectric properties indicate that the Curie temperature?Tc?rose to 138 ?.And BT-BKT-xNb ceramic obtains the excellent properties when x=0.1% mol: ?RT=798.84?·cm,lg??max/?min?= 3.9.?3?The influence of the SnO₂ doping on the microstructure,phase composition,phase structure and electric properties of(Ba_0.96Bi_0.02K_0.02)Ti_0.9985Nb_0.0015O_3-xSnO₂?x=0.01,0.02,0.03,0.04mol??abbreviated as BT-BKT-Nb-xSnO₂?were investigated.The results indicate that all the samples posses a typical perovskite structure solid solution.When the content of SnO₂ increases,the microstructure exhibits relatively homogeneous,and SnO₂ promotes grain growth within the solution limit.The results of dielectric properties indicate that the Curie temperature?Tc?rose to 172?.BT-BKT-Nb-x SnO₂ ceramic obtains excellent properties when x=0.03,?RT= 295.16?·cm,lg??max/?min?= 4.139.?4?The influence of the CuO doping on the microstructure,phase composition,phase structure and electric properties of(Ba_0.96Bi_0.02K_0.02)Ti_0.9985Nb_0.0015O_3-xCuO?x=0.01,0.02,0.03,0.04mol??abbreviated as BT-BKT-Nb-x CuO?were investigated.From the XRD patterns of BT-BKT-Nb-xCuO,all samples are of typical perovskite phase when x?0.02.However,When x>0.02,the appearance of characteristic peaks can not be clearly observed in the XRD patterns.It is found that CuO has a limited solubility in BT-BKT ceramic.From the SEM of BT-BKT-Nb-xCuO ceramics,CuO promotes grain growth within the solution limit.The results of dielectric properties indicate that the Curie temperature?Tc?rose to 180?.BT-BKT-Nb-xCuO ceramic obtains excellent properties when x=0.02,?RT = 601.31?·cm,lg??max/?min?= 3.399.