Dielectric characteristics of Ca(1-x)ZnxLa4Ti5O17 ceramics at microwave frequencies

In this paper, microwave dielectric properties of Ca(1-x)ZnxLa4Ti5O17 ceramics have been studied for application in mobile communications. The starting raw chemicals were high-purity CaCO3, ZnO, La2O3, TiO2 and CuO powders. The composition prepared was Ca(1-x)ZnxLa4Ti5O17 with x=0, 0.01, and 0.05. Ca(1-x)ZnxLa4Ti5O17 was added 0.5 wt.% CuO to lower the sintering temperature. Specimens were prepared using the conventional mixed-oxide method. The specimens were sintered at 1350 OC, 1400 OC, 1450 OC and 1500 OC for 4h. After sintering, the phases of the samples were investigated by X-ray diffraction. Scanning electron microscopic (SEM) was employed to examine the microstructures of the specimens. The bulk densities of the specimens were measured by the Archimedes method. The microwave dielectric properties of the specimens were measured by the postresonator method developed by Hakki and Coleman. It is found the X-ray diffraction pattern exhibited no phas´e difference with different Zn content. The relationships between dielectric constant and sintering temperature revealed the same trend with those between apparent densities and sintering temperatures. A dielectric constant value of 57 was obtained for Ca0.95Zn0.05La4Ti5O17 ceramics sintered at 1400 OC for 4 h. The quality decreases with the increasing of Zn content. A quality factor of 16100 GHz was obtained for CaLa4Ti5O17 ceramics sintered at 1450 OC for 4 h. The temperature coefficient of resonant frequency ( ) values were moved to the positive direction as the Zn content increased. A of -1.5 ppm/OC was obtained for Ca0.95Zn0.05La4Ti5O17 ceramics sintered at 1350 OC for 4 h.