Dielectric Properties Of (1-x)CaTiO₃-xCa(Zn_1/3Nb_2/3)O₃ Solid Solution Ceramics At Microwave Frequency

In the past three decades, the proliferation of the research about microwave dielectric ceramics makes the rapid progress of the technology of the microwave communication. The requirement of the properties of these ceramics that must possess high permittivity (r), low dielectric loss (Q= tan -1 ) and near-zero temperature coefficient of resonant frequency (tf) eliminates the use of many conventional high dielectric constant materials such as ferroelectrics. In this study, the microwave dielectric properties of the system made of CaTiO3 that exhibits a positive tf and Ca(Zni/3Nba/3)O3 that possesses a negative tf have been investigated to obtain a new microwave dielectric ceramic, which exhibits a high er, a low dielectric loss and a near-zero tf.The complete solid solution system was produced by the solid reaction. The microstructure of the ceramics was characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD shows that the ceramics exhibit the orthorhombic perovskite structure for different compositions x. SEM shows that the porosity of the samples is very low. The various rules of the dielectric properties are the non-monotonic mixture-like behavior by using the HP network analyzer to collect the data at microwave properties for the samples as x increases from 0 to 1. The dielectric constant decreases from 180 to 36, and the quality factor Q f increase from 3600 to 16000GHz, and the temperature coefficient of the resonant frequency tf varies from 800 to -28 ppm/ C.When x=0.7, the best combination of dielectric properties, a near zero tf~-6 ppm/C, Q f ~ 10860GHz and r~51, is obtained. The permittivity has been calculated by using the Clausius-Mosotti equation. The calculated permittivity shows the same trend as the measured ones between which the difference has been analyzed qualitatively.The effect of the CuO on the 0.3CaTiO3-0.7Ca(Zn1/3Nb2/3)O3 system has also been investigated. When a little CuO powder is doped, the sintering temperature and the microwave dielectric loss of the system will decrease. When 1.0wt% CuO is doped, the best combination of microwave dielectric properties,ppm/C, Q f~13900GHz and r~51.7 sintered at 1200 C for 4 hours is obtained.