Mg5Nb4TiO17 ceramic was prepared by the conventional solid-state route for the first time and its microwave dielectric properties were investigated. The crystal structure and microstructure were analyzed using X-ray diffraction and scanning electron microscopy techniques. With increasing sintering temperature, the dielectric constant (εr) and quality factor (Q×f) increased firstly and then decreased, while the τf nearly unchanged. Mg5(NbTi)4O15-MgNb2O6 composite ceramics sintered at 1200 oC exhibits microwave dielectric properties of εr=15.1, Q×f=34,266.6 GHz (at 8.5GHz), τf=-63.8 ppm/oC.

The rock-salt structure Li2MgTiO4 ceramics were prepared by reaction sintering method and its microwave dielectric properties were investigated. The crystal structure and microstructure were analyzed using X-ray diffraction and scanning electron microscopy techniques. XRD showed that main phase Li2MgTiO4 combined with minor second phase Mg2TiO4 were formed after 1250-1350 oC sintering. The microwave dielectric properties of Li2MgTiO4 ceramics exhibited a significant depend on the density and to some extent on the morphology of the grains. Li2MgTiO4 sintered at 1325 oC/5h exhibits microwave dielectric properties of εr=13.2, Q×f=44 711 GHz (at 9.9 GHz ) and τf=-31ppm/oC.

The effects of Li2CO3-V2O5 (LV) co-doped on the sinterability, phase compositions and microwave dielectric properties of Mg4Nb2O9-CaTiO3 composite ceramics have been investigated. The phase compositions and microstructure were analyzed using X-ray diffraction, energy dispersive X-ray analysis and scanning electron microscopy techniques. The densification sintering temperature is lowed from 1275oC to 1200oC with an amount LV addition. For the specimen with 1.5 wt% LV addition sintered at 1200oC for 5 h exhibited dielectric properties: εr=23, Q·f=24 000 GHz (at 7.7GHz ), τf =1.0 ppm/oC. These properties were correlated with the formation of non-stoichiometric compound Mg4(Nb1-xTix)2O9-δ.

Li2ZnTi3O8ceramics were prepared by reaction-sintering process (calcination free). The crystal phase and microstructure were investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). A pure phase of Li2ZnTi3O8ceramics sintered at 1075 °C-1150 °C with cubic spinel structure was confirmed by XRD. The microwave dielectric properties (εr,Qxf) of Li2ZnTi3O8ceramics were strongly dependent on the densification and grain size. The τfof Li2ZnTi3O8ceramics was almost independent with the sintering temperatures. In particular, Li2ZnTi3O8ceramics by reaction-sintering method sintered at 1125 °C for 5 h exhibited good combination microwave dielectric properties of εr=21.7, Q×f=70 500 GHz (at 7.5 GHz) and τf=-13 ppm/°C.

The effects of Li0.8Ca0.2F1.2 doped on the sinterability, phase constitutions and microwave dielectric properties of (Mg0.95Zn0.05)2(Ti0.8Sn0.2)O4 (MZTS) ceramics were investigated. The crystal structure was analyzed using X-ray diffraction. With 3.0 wt% Li0.8Ca0.2F1.2 addition, the densification sintering of MZTS ceramics was significantly lowed from 1325 oC to 1150 oC due to the liquid phase sintering. Secondary phases CaTiO3 and MgO were formed by reaction between MZTS and CaF2. 3.0wt% Li0.8Ca0.2F1.2-doped MZTS ceramics at 1150 oC for 5 h exhibited dielectric properties: εr=13.4, Qxf=46 672.3 GHz (at 9.3 GHz).