Study On Microwave Dielectric Properties Of Li₂ATi₃O₈?A=Zn, Mg, Co? Ceramics And Its Design For Component

Li₂ATi₃O₈?A=Zn, Mg, Co? microwave dielectric ceramics are promising for low temperature co-fired ceramic applications due to their excellent microwave properties, low sintering temperature as well as good chemical compatibility with silver. The Li₂ATi₃O₈?A=Zn, Mg, Co? ceramics were chosen as research subject in this dissertation. The relationships among phase compositions, microstructures and microwave dielectric properties of the ceramics were systematically investigated by DSC-DTG, XRD, SEM, Raman spectroscopy, network analyzer, etc. Meanwhile, the dielectric mechanisms were investigated.Firstly, the Li₂ATi₃O₈?A=Zn, Mg, Co? ceramics were prepared by the conventional solid-state ceramic method. The optimized sintering process and relative microwave dielectric properties were obtained. The effects of molecular polarization and packing fraction on microwave dielectric properties were studied based on the above results. The highest relative density and microwave dielectric properties of Li2 Zn Ti3O8, Li2 Mg Ti3O8 and Li2 Co Ti3O8 ceramics were achieved when sintered at 1075, 1050 and 1025?, respectively. Li2 Mg Ti3O8 ceramic owned the highest dielectric constant which may be caused by its large ionic polarization; Li2 Zn Ti3O8 ceramic possessed the lowest dielectric loss due to its utmost relative density and packing fraction; Temperature coefficient of resonance frequency was mainly related to its composition, which was 4.02, 5.2 and-12.4 ppm/? for Li2 Mg Ti3O8, Li2 Co Ti3O8 and Li2 Zn Ti3O8 ceramics, respectively.Then, the effects of Mg2+ and Co2+ substitution for Zn2+ in Li2 Zn Ti3O8 ceramic on its temperature coefficient of resonance frequency were studied. The mechanism of molecular polarization, packing fraction, lattice vibration and bond valence varied with A-site ion on microwave dielectric properties were investigated. After Mg2+ doping, the cell volume increased, packing fraction decreased, the Raman peak of A1g?1? mode shifted to lower frequency and the FWHM?Full Width at Half Maximun? narrowed, the lattice vibration energy decreased, thus increasing the dielectric loss; the bond valence between cation and oxygen increased inducing a nero-zero temperature coefficient of resonance frequency. Co2+ substitution increased the tilting of Ti O6 octahedron, where the increasing restoring force lowered the polarization, resulting in a decrease in dielectric constant; the decrease in packing fraction and cation ordering caused the decrease of Q×f value; the temperature coefficient of resonance frequency shifted to zero with large bond valence; Li2Co0.6Zn0.4Ti3O8 ceramic exhibited good comprehensive dielectric properties of ?r=25.5,Q×f=59358GHz,?f=-1.5ppm/?.Using the Li2Co0.6Zn0.4Ti3O8 as the substrate, a rectangular microstrip patch antenna with central frequency at 2.45 GHz was designed by HFSS software. The central frequency was influenced largely by the length of the patch. The return loss and VSWR were satisfied for application after optimization. The central frequency of the antenna located at 2.45 GHz with the patch length of 10.058 and the width of 15.55 millimeter.