Microwave Dielectric Resonator Ceramics Of High-Q Value For The 3G Mobile Communication Base Stations

Based on the development, prospect and research actuality of resonator ceramics with high Q value based on 3G mobile communications, Ba(Co,Zn)_1/3Nb_2/3O₃-based ceramics are chosen as research objective in this dissertation. The relationships among formula, sintering process, microstructure and microwave dielectric properties have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectrum and network analyzer, etc.Sintering characteristic, phase compositions, ion ordering and microwave dielectric properties of Ba_1-xZn_1/3Nb_2/3O₃(x=0⁰.02) ceramics had been studied. It shows that moderate Ba-deficiency do not change the phase compositions of the Ba_1-xZn_1/3Nb_2/3O₃ ceramics, but can effectively improve the sinterability of the ceramics, lower the densification temperature by about 100℃, improve the cation ordering and Q×f values. The highest degree of cation ordering and good Q×f value 66532GHz exists in the x=0.01 samples when sintered at 1450℃. And then, the sintering processes such as calcining temperature and cooling rate of the Ba_1-xZn_1/3Nb_2/3O₃ (x=0.01) ceramics have been researched systematically, and the optimal sintering process parameters have been determined which are 1100℃and 5℃/h, respectively, in which sintering conditions the microwave dielectric properties are as follows:ε_r=39.8, Q×f=77719GHz,Ï„_f=+24.5ppm/℃.Sintering characteristic, phase compositions, grain growth, ion ordering and microwave dielectric properties of Ba_0.99(Co_1-xZn_x)_1/3Nb_2/3O₃ (x=0⁰.8) ceramics are investigated. As x increases, ceramics are easier to densely sintered, the dielectric constant gradually increased and the temperature coefficient of resonant frequency shift to the positive direction. Two-step sintering can significantly improve the density and Q×f values of the ceramics. For the sample with x=0.2, after two-step sintering at 1490℃, Ba_0.99 (Co_1-xZn_x) _1/3Nb_2/3O₃ (x = 0.2) ceramic can get a higher density and cation ordering, and a optimal microwave dielectric properties with Q×f=79852GHz,ε_r=33.1 andÏ„_f=-2.6ppm/℃can be obtained.For the Ba_0.99(Co_0.7Zn_0.3)_1/3Nb_2/3O₃ ceramics, the sinterability can be improved when ceramics are doped with moderate CeO₂. The degree of cation ordering increases with gradually increasing the amount of CeO₂ doping, and then decreases with further increasing the amount of CeO₂. When doped with 0.25wt. %CeO₂, the highest degree of cation ordering can be obtained for the Ba_0.99(Co_0.7Zn_0.3)_1/3Nb_2/3O₃ ceramics. After the two-step sintering at 1490℃, an optimal microwave dielectric properties can be obtained for the Ba_0.99(Co_0.7Zn_0.3)_1/3Nb_2/3O₃+0.25wt. %CeO₂ ceramics:ε_r=34.3 , Q×f=89966GHz ,Ï„_f=+4.7ppm/℃.For the stoichiometric Ba(Co_0.7Zn_0.3)_1/3Nb_2/3O₃ ceramics, the sinterability can also be improved when ceramics are doped with moderate CeO₂, and the degree of cation ordering increases with gradually increasing the amount of CeO₂ doping, and then decreases with further increasing the amount of CeO₂. When doped with 0.4wt. %CeO₂, the highest degree of cation ordering can be obtained for the Ba(Co_0.7Zn_0.3)_1/3Nb_2/3O₃ ceramics. After a two-step sintering at 1500℃, an optimal microwave dielectric properties can be obtained for the Ba(Co_0.7Zn_0.3)_1/3Nb_2/3O₃+0.4wt. %CeO₂ ceramics:ε_r=33.3,Q×f=100144GHz,Ï„_f=+4.8 ppm/℃.For the Ba(Co_1-xZn_x)_1/3Nb_2/3O₃+0.4wt. %CeO₂ ceramics sintered at 1490℃, as x increases, the grain sizes increase gradually, and the degree of cation ordering increases firstly and then decreases to 0. The highest degree of cation ordering can be obtained for the samples with x=0.4. Good microwave dielectric properties ofε_r=34.3,Q×f=65330GHz,Ï„_f=+8.9 ppm/℃can be obtained for the Ba(Co0.6Zn0.4)_1/3Nb_2/3O₃+ 0.4wt. %CeO₂ ceramics.