| As key materials of microwave resonator and microwave filter, microwave dielectric ceramics have been utilized in microwave communication systems. Among them, CaTiO3 ceramic exhibits high dielectric properties of r (170), Qf value (3600GHz) and a large positive value(800ppm).Based on the relationship among the composition, microstructure and dielectric properties, the modified system ceramics based on CaTiO3 were produced and their dielectric characteristics were discussed. The influences of A-site and B-site as well as both of them substitution on the microstructures and dielectric properties of CaTiO3-based system ceramics were studied. The main content are as following:Because Ca(Mg1/3Nb2/3)O3 ceramics possesses dielectric constant =28, high-quality factor (Qf value=58,000 GHz), and negative value (-48ppm). Appropriable temperature coefficient of resonant frequency can be obtained by employing solid solutions of (1-x) CaTiO3 -xCa(Mg1/3Nb2/3)O3. The crystal structures and the microwave dielectric properties of CMNT perovskite-type ceramic system have been investigated. With x=0.6, (1-x)CaTiO3-xCa(Mg1/3Nb2/3)O3 (CMNT)solid solution possesses the dielectric properties of dielectric constant = 49.54, Qf values = 28,900 (at 6.7 GHz) and value =-22 ppm .Further improvement of the dielectric properties can be achieved by A-site substitution in CMNT (x=0.6) ceramic. The research results show: the effect of substitution of A-site ions (La3+ Nd3+ Sr2+) on the microstructure and microwave properties of CMNT ceramic is different. Compared with Nd3 Sr2+ substitution, it is found that La3+ substitution can improve the microwave properties of CMNT ceramic. CLMNT ceramic exhibits microwave dielectric properties as following: =34, Qf value=31400GHz and value =-9ppm.Meanwhile, the microstructure and microwave dielectric properties of Ba2+ ions A-site substitution modified CMNT ceramic were investigated also. The result reveals that the microwave dielectric properties of (Ca1-xBax) [(Mg1/3Nb2/3)o.6Ti0.4]O3 system ceramics are related with dispersing of Ba2+ ions in ceramics. When x=0.85, (Ca0.15 Ba0.85 )[(Mg1/3Nb2/3)0.6Ti0.4]O3 ceramic withsingle perovskite-type structure has the best microwave dielectric properties: =31, Qf value = 44000GHz(at 8.5GHz), =10.81ppm/The effect of the substitution of B-site ions (Ta Sn Zr4) on the microstructure and microwave properties of CMNT ceramics has been investigated. It is found that the change of crystal structure of CMNT with B-site Ta5+ ions substitution is smaller than that of CMNT ceramics with Sn4, Zr ions B-site substitution. With increasing of Ta substitution, CMNTT ceramics possesses high Qf value 35600 GHz (at 8.6GHz) , = 43.38, and value- 1.46ppm.The relation between microstructure and dielectric properties of A-site La3+ ions and B-site Ta5+ ions harmonizing substitution in CMNT ceramics has been studied. With La and Ta substitution, CLMNTT ceramics exhibits excellent dielectric properties: =36, Qf value = 38050GHz (at 7.5GHz), 9.58ppmOn the base of experiments and related dielectric theories, the modifying mechanism and intrinsic microwave dielectric mechanism of ceramics based on CaTiO are discussed. The changes of microstructure inside the La substitution ceramics based on CaTiO lead to the depression of ions dipole polarization and reduce the dielectric constant. The Ta can effectively enhance the inertial mass and raise the attraction between positive and negative ions. In this way, the dielectric loss can be greatly decreased. The improvement of temperature coefficient of resonant frequency in modified ceramics based CaTiO3 system can be attributed to the distortion of octahedra inside materials.
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