Study On Low-temperature Preparation And Property Regulation Of Middle And High Permittivity Microwave Ceramics

In recent years, with the rapid development of wireless communication technology, new requirement about miniaturization, high quality and low cost of microwave device based on microwave dielectric ceramics has been proposed. Currently, low firing and low temperature cofiring(LTCC) dielectric materials have mostly focused on these microwave ceramic system with low permittivity. However, high permittivity microwave dielectric ceramics often have some disadvantages such as high sintering temperature, large ηf and low quality factor. Therefore, it is necessary to search for novel microwave dielectric materials with low sintering temperature(≤1100 ℃) and good performance(εr ≥ 20, Qf ≥5000 GHz and ηf = ±10 ppm/℃).New middle and high permittivity microwave ceramics have been prepared based on principles of composite material. The sintering characteristics, crystal structures, microstructures and dielectric properties of low firing microwave dielectric ceramics were thoroughly investigated by using X-ray diffractometer(XRD), scanning electron microscope(SEM) and dielectric propertiy tester. The obtained results are as follows:1.(1-x)Li3NbO4- x Ca0.8Sr0.2TiO3(x = 0.1-0.4) system: XRD and EDS results suggest that all samples adopt two phase of perovskite and Li3NbO4. With the value of x increasing, εr increases from 18.6 to 31.2, the value of Qf decreases from 86962 GHZ to 9472 GHZ, ηf increases from-30 ppm/℃ to +119 ppm/℃. The experimental observation is consistent with theoretical calculated results. The sample of x = 0.2 sintered at 1075℃ exhibits the optimum dielectric properties: εr = 21.4, Qf = 49276 GHz and ηf = + 5.15 ppm/℃.2.(1-x)BiVO4- x Li0.5Re0.5WO4(Re = La, Nd, Sm)(x = 0.05- 0.11) system: XRD results suggest that all ceramic samples adopt monoclinic BiVO4 structure within limits of substitution and the lattice parameters and unit cell volumes increases with increasing x value. SEM observation shows that the best sintering temperature of the system is 750℃. 0.91BiVO4- 0.09Li0.5La0.5WO4 exhibits the optimum dielectric properties: εr = 76.65, Qf = 6789.4 GHz and ηf = + 7.3 ppm/℃. The best dielectric propertiesof εr = 71.8, Qf = 7481.7 GHz and ηf = 0.8 ppm/℃ are achieved for 0.92BiVO4- 0.08Li0.5 Nd0.5WO4.3.(1-x)Ca0.8Sr0.2TiO3- xLi0.5Sm0.5Ti O3 system: XRD results shows that all samples adopt orthorthombic perovskite structure within limits of substitution. 0.2CST-0.8LST sintered at 1250℃ possesses the best dielectric properties. The CST-LST ceramics with 5wt% BaCu(B2O5) sintered at 950℃ exhibits single phase perovskite structure, together with the optimum microwave dielectric properties of εr = 66.7, Qf = 3222 GHZ, ηf = 21.3 ppm/℃. Adding TiO2 improves the microwave properties. Typically, the CST–LST+5 wt%BCB+1.5 wt%TiO2 sintered at 950℃ shows εr = 71.6, Qf = 3441 GHZ, ηf = 10.8 ppm/℃. Compatibility with Ag electrode indicates that this material is suitable for low temperature co-fired ceramics.