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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 V 2 O 5 and Li 2 CO 3 on the sinterability and microwave dielectric properties of Mg 4 Nb 2 O 9 (MN) ceramics were investigated. With addition of 1.5wt% V 2 O 5 , the dielectric constant (e) and Q · ƒ value of MN ceramics sintered at 1,000°C are comparable to those of pure MN sintered at 1,400°C. The good results are because of the enhancement of the density by liquid sintering at the lower temperatures. With the mixtures of V 2 O 5 and Li 2 CO 3 , the sintering temperature of MN was further reduced to 925°C at the expense of the quality factor (Q · ƒ) value. Typically, e of 13.7 and Q · ƒ value of 78,000 GHz were obtained for the specimens with mixtures of 1.5wt% V 2 O 5 and 1.5wt% Li 2 CO 3 and sintered at 925°C for 5 h.

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.