Study On Microstructure And Dielectric Properties Of Ca4la2ti5o17-based Microwave Ceramics

Microwave dielectric ceramics have been widely used in microwave communication field such as cellular phones, global positioning systems, and satellite broadcasting and so on. With the rapid development of microwave communication technology, we constantly need new high performance microwave dielectric ceramics.Ca4La2Ti5O17based-microwave ceramic materials were prepared by a solid-state reaction method. The effects of substitution and co-doping on sintering characteristics, crystal structure, microstructure and dielectric properties of Ca4La2Ti5O17microwave dielectric ceramics were investigated using X-ray diffractometer (XRD), scanning electron microscope (SEM) and dielectric properties measuring. The obtained results are as follows:1. Ca4-xSrxLa2Ti5O17(x=0-3) system:XRD results suggest all ceramic samples adopt orthorthombic perovskite structure within limits of substitution, and the lattice parameters and unit cell volume increase with increasing x value. SEM results also reveal no evidence of secondary phase and the substitution of Sr2+for Ca2+restrains the grain growth.The εr of sintered ceramics increases from72to90,the Q×f value decreases from15070to3216GHz and the τf value varies from125to175ppm/℃with increasing x from0to3.2. Ca4La2Ti5-x(Mg1/3Nb2/3)xO17(x=0-4) system:XRD results indicate all ceramic samples show the orthorthombic perovskite structure within limits of substitution, the unit cell volume increases with increasing x value. SEM results also display no evidence of secondary phase and the substitution of (Mg1/3Nb2/3)4+for Ti4+promotes the grain growth. With increasing x from0to4,the εr of sintered ceramics decreases from71.85to35.23,the Q×f value increases from15070to21277GHz and the τf value decreases from125to-16.7ppm/℃. Ca4La2Ti2(MgNb2)O17microwave ceramic was achieved at x=3, which has optimized microwave dielectric properties with εr=40.45, Q×f=19123GHz,τf=1.62ppm/℃.3.(1-x)Ca4La2Ti5O17-xNdAlO3(x=0-0.7) system:XRD results demonstrate all ceramic samples display the orthorthombic perovskite structure,the unit cell volume decreases with increasing x value. SEM results also suggest no evidence of secondary phase and doping NdAlO3prevents the grain growth. The εr of sintered ceramics decreases from72to32,the Q×f value decreases from15070to13251GHz and the τf value varies from125to-33.1ppm/℃with an increasing in x value from0to0.7. 0.4Ca4La2Ti5O17-0.6NdAlO3microwave ceramic of optimized microwave dielectric properties is achieved at x=0.6, with εr=41.8, Q×f=13781GHz, τf=-6.5ppm/℃.