Study On Dielectric Properties Of Perovskite Niobate Based Ceramics

Perovskite niobate is a kind of complex ceramic oxides with unique crystal structure.Generically these compounds have a chemical formula ABO₃. Due to doped crystals defectstructures present excellent dielectric, piezoelectric and ferroelectric properties, they arewidely used in various fields including solid dielectrics, sensors, resistors and replacingprecious metals. It is a hot topic in material, chemical and physical field. In recently, ceramicsbased on K_0.5Na_0.5NbO₃（KNN） and BaFe_0.5Nb_0.5O₃（BFN） rouse great interesting in the fieldof piezoelectric and giant dielectric hotspot. Therefore, Perovskite niobate lead-free ceramicsare considered to be promising material as the practical piezoelectric, dielectric.Lead-free piezoelectric ceramic systems of K_0.5Na_0.5Nb_1-xVxO₃-0.01CuO （KNNV-x）,（1-x）K_0.5Na_0.5NbO_3-xSrMnO₃（KNN-xSM） and K_0.5Na_0.5Nb_1-xCuxO₃（1-x/2）（KNNC-x） wereprepared by solid state reaction technique with different sintering aids. The phase,microstructure, sintered temperature and electrical properties were investigated doped withdifferent content of V₂O₅、SrMnO₃and CuO for KNN. Experimental results show that theremnant polarization Pr decreases from9.7μC/cm²to1.98μC/cm², while the piezoelectricconstant increases from36pC/N to78pC/N when doping amount of V₂O₅from2%to16%.The maximum remnant polarization can reach20μC/cm²for KNN ceramics doped with4%mol SrMnO₃. Normal ferroelectric phase transition converts to diffuse ferroelectric phasetransition for KNN ceramics dependence on SrMnO₃content from4%to8%. All the KNNceramics doped with CuO are obtained saturated ferroelectric hysteresis loops. Furthermore,the piezoelectric constant increases from87pC/N to115pC/N dependence on CuO content.The maximum Pr can reach20μC/cm²for doping1%mol CuO KNN ceramic which exhibit aclear double hysteresis loop.The solid solution of （1-x）BaFe_0.5Nb_0.5O_3-xBi0.5Na0.5TiO₃（BFN-xBNT） and（1-x）BaFe_0.5Nb_0.5O_3-xBiYbO₃（BFN-xBY） were prepared by two-step method of traditionalsolid state technology and their phase structure, dielectric properties and dielectric relaxation mechanism of conductance were studied. Another obvious relaxation peak appears for BFNceramics when doped with BNT or BY, and the relaxation peak moves to lower temperaturewith increase of doped concentration. The dielectric constant and dielectric loss decrease ofBFN ceramics firstly and then increase with increasing content of BNT and BY at1MHz atroom temperature. The temperature and frequency stability of the dielectric constant for BFNceramics were greatly enhanced when doping2%mol BNT or BY under1MHz at roomtemperature.