The microwave dielectric properties of ZrO2-SnO2-TiO2 （ZST） system ceramics were stu- died as a function of the amount of Sb2O5 dopant. With the addition of 0—0.50/0 Sb2O5 （molar ratio）, the substitution of Ti 4+ ions with Sb 5+ ions decreased the sintering temperature and increased the quality factor Q due to the reduction of oxygen vacancies. When the amount of Sb 5+ increased further （above 0.50/0）, Q was decreased by increasing the electron concentration. When the system doped with 0.50/0 Sb2O5 was sintered at 1 150 ℃ for 6 h, the relative dielectric constant ε, Qf0, and the temperature coefficient of resonant frequency （TCF） were 38.46, 44 500 GHz,20.0×10 -6 /℃, respectively, at 6 GHz.
High performance X8R dielectric ceramics were prepared by dopingBi2O3 to BaTiO3-based ceramics.The effect of small amounts(≤1.2 mol%) ofBi2O3 additive on the microstructure and dielectric properties of BaTiO3-based ceramics have been investigated.The Bi2O3 ,acting as a sintering additive,can effectively lower the sintering temperature of BaTiO3-based ceramics from 1300 to 1130 °C.The bulk density of BaTiO3-based ceramics increased and reached the maximum value with increasingBi2O3 content.The dielectric constant increased with increasingBi2O3 until it reached the maximum value with 0.8 mol%Bi2O3 additive,and the dielectric loss decreased with increasingBi2O3 content.Optimal dielectric properties of ε=2470,tanδ=0.011 and △ε/ε 25 ≤±9%(-55-150 °C) were obtained for the BaTiO3-based ceramics doped with 0.8 mol%Bi2O3 sintered at 1130 °C for 6 h.
Shunhua Wu Xuesong Wei Xiaoyong Wang Hongxing Yang Shunqi Gao
The structures and dielectric properties of Ba_(6-3x)Nd_(8+2x)Ti_(18)O_(54)system(x=2/3)doped with different contents of Bi_2O_3,whose final molecular formula is Ba_(6-3x)(Nd_(1-y)Bi_y)_(8+2x)Ti_(18)O_(54)were investigated.It is indicated that the dielectric constant increases greatly whereas Q value(f_0=4 GHz)decreases with the increase of Bi_2O_3 content.However,the temperature coefficient could be controlled below 0±30×10^(-6)/℃in the experiment. These phenomena are related to the appearance of a new phase,Bi_4Ti_3O_(12),which has high dielectric constant. Also,that Bi^(3+)(0.13 nm)substitutes for Nd^(3+)(0.099 5 nm)will increase the unit cell volume,which will lead to the enlargement of the octahedron B site occupied by Ti^(4+).So the spontaneous polarization of Ti^(4+)ions will be strengthened.Besides,Bi^(3+)will fill up some vacancies which Ba^(2+)or Nd^(3+)ions leave in two Al sites and four A2 sites.More positive ions polarize,which also contributes to higher dielectric constant.The samples got with the optimium properties are sintered at 1200℃for 4 h,when 3,=0.25,ε≈110,Q≈5 400(f_0=4 GHz),TCC=4.7×10^(-6)/℃;When y=0.3,ε≈120,Q≈5 000(f_0=4 GHz),TCC=24×10^(-6)/℃.
The microwave dielectric properties and microstructure of BaTi4.3ZnyO9.6+y +0.02 mol% SnO2+0.01 mol% MnCO3+x mol% Nb2O5(x=0-0.05, y=0-0.08) system ceramics were studied as a function of the amount of ZnO and Nb2O5 doped. Addition of (y=0-0.05) ZnO and (x=0-0.025) Nb2O5 enhanced the reactivity and decreased the sintering temperature effectively. It also increased the dielectric constantεr and quality factor Q(=1/tanδ) of the system due to the substitution of Ti4+ ions with incorporating Zn2+and Nb5+ ions, which was analyzed by the reaction ZnO+Nb2O5+ 3 TiTx i→ZnTi+ 2NbT i·+3TiO2. When the system doped with (y=0.05) ZnO and (x=0.025) Nb2O5 were sintered at 1 160 ℃ for 6 h, the εr, Qf0 value andτf were 36.5, 42 000 GHz, and+1.8 ppm/℃, re-spectively, at 5 GHz.
