Preparation And Properties Of Lead-free Perovskite With High Dielectric Ceramics

Dielectric ceramics with high dielectric constant are made into capacitors, ceramic filters,resonators, and the memory, which are widely used in energy, medicine, military, space, cars,home appliances and other high-tech fields. In recently, K0.5Na0.5NbO3、Bi0.5Na0.5TiO3andBaTiO3ceramics will be substitute for Pb(Zr,Ti)O3-based materials, which rouse greatinteresting in the field of dielectric hotspot.However, this kind of electronic ceramic materialshave poor dielectric temperature stability, not suitable for actual production application.Therefore, improved the dielectric temperature by doping other chemical elements are veryimportant.In this work,(1-x)(Na0.5K0.5)NbO3-xBi(Mg0.5Ti0.5)O3(KNN-BMT)、(1-x)Bi0.5Na0.5TiO3s(solid state method)-xBi0.5Na0.5TiO3g(sol-gel method)-0.06BaTiO3(BNTs-BNTg-BT)、LiCuNb3O9(LCN)、(1-x)BaTiO3-xLiCuNb3O9(BT-LCN) systems wereprepared by solid-state reaction method. The phase structure, microstructure and electricproperties of ceramic samples were investigated in detail.(1)(1-x)KNN-xBMT (0≤x≤0.04) lead-free dielectric ceramics. X-ray diffractionrevealed that the phase of (1-x)KNN-xBMT transformed from orthorhombic to tetragonalwith increasing the content of BMT at room temperature. The study of dielectric propertiesillustrated that both peaks of orthorhombic to tetragonal (TO-T) and tetragonal to cubic (TC)phase transition shifted to lower temperature. Through adding BMT, the electric properties ofKNN-BMT were obviously enhanced. The optimized piezoelectric and ferroelectricproperties with d33=127pC/N, Kp=36.58%, Pr=22.1μC/cm2were obtained for x=0.01.(2)(1-x) BNTs-xBNTg-0.06BT(0≤x≤1) lead-free dielectric ceramics. A morphotropicphase boundary (MPB) was found out in the system. As x content increased, the dielectricmaximum value reduces significantly. And the Bi0.5Na0.5TiO3g also makes depolarizationtemperature (Td) decreased which make the antiferroelectric zone larger and more stable. TheBi0.5Na0.5TiO3g significantly disrupts the long-range ferroelectric order dominant of theceramics leading to a degradation of the remanent polarization and coercive field.(3) LiCuNb3O9lead-free and giant dielectric ceramics. Structural analysis of theceramics indicated a cubic perovskite structure. When the temperatures are from250to550oC at10kHz, LCN ceramics exhibited giant dielectric constant with relatively steadyε′~2.0-2.3×105. Besides, the giant dielectric behavior of the LCN ceramic can be wellinterpreted by the Maxwell-Wagner effect.(4)(1-x)BT-xLCN(0≤x≤0.08) lead-free dielectric ceramics. The samples exhibited atetragonal to pseudocubic phase transition. When x=0.08，the temperature variation of capacitance(Δε/ε30oC<30%) of BT-LCN samples were obtained in temperature range from30℃to200℃. For0.02≤x≤0.08, the samples posses high dielectric constant (>1000) andthe temperature variation of capacitance (Δε/ε30oC) was within5%in temperature range of30℃~100℃, especially.