Research On Fabrication And Properties Of Niobium Titanate System Microwave Dielectric Ceramics

As key materials of microwave resonator and microwave filter, microwave dielectric ceramics have been utilized in microwave communication systems. Based on the relationship among the composition, microstructure and dielectric properties, the microwave dielectric ceramics are fabricated via traditional solid state method and are analyzed using XRD, SEM and network analyzer. The main content are as following:First of all, ZnNb₂O₆ ceramics are prepared by solid state method. The effect of calcining temperature, sintering temperature and extra ZnO on the microstructure and microwave properties has been investigated. The best microwave properties(ε_r = 24.02,Q^*f = 32394GHz,Ï„_f =-87.07ppm/℃) are reached when the calcining temperature is 800℃, sintering temperature is 1150℃and extra 1at% ZnO are added.Further improvement of dielectric properties can be achieved by A-site and B-site substitution in ZnNb₂O₆. According to the ion radii size, Y(Ti_0.5Nb_0.5)₂O₆, LaTiNbO₆, SmTiNbO₆ are fabricated. For Y(Ti_0.5Nb_0.5)₂O₆ microwave dielectric ceramcis, the best microwave dielectric properties( r = 21.36,Q^*f = 19607GHz,Ï„_f =-64.27ppm/℃) are obtained when calcining temperature is 1350℃, sintering temperature is 1500℃and it belongs to orthorhombic phase. For LaTiNbO₆ ceramics, there is a phase transition when calcining temperature is 1200℃from orthorhombic phase to monoclinic phase. But the best microwave dielectric properties ( r = 22.87,Q^*f = 17822GHz,Ï„_f =-67.39ppm/℃) are obtained when calcining temperature is 1300℃and the sintering temperature is 1000℃. For SmTiNbO₆ ceramics, the best microwave dielectric properties ( r =49.55,Q^*f = 19694GHz,Ï„_f =50.05ppm/℃) are got when calcining temperature is 1340℃, sintering temperature is 1440℃and it belongs to orthorhombic phase. SmTiNbO₆ microwave dielectric ceramics have positiveÏ„_f. It is possible to prepare a kind of ceramics which have a near zeroÏ„_f if we composite ZnNb₂O₆ and SmTiNbO₆ together which have oppositeÏ„_f sign.ZnNb₂O₆ reacted with SmTiNbO₆ when (1-x)ZnNb₂O₆-xSmTiNbO₆ composite ceramics are tried to be prepared and the phase composition changed a lot with x is bigger and bigger. When x is less than _0.5,the composition are ZnNb₂O₆, ZnTiNb₂O₈, SmNbO₄; when x is _0.5, the composition are ZnTiNb₂O₈, SmNbO₄; when x is bigger than _0.5 but less than 0.733, the composition are ZnTiNb₂O₈, (Zn_0.15Nb_0.3Ti_0.55)O₂, SmNbO₄; when x is 0.733, the composition are (Zn_0.15Nb_0.3Ti_0.55)O₂, SmNbO₄ and when x is bigger than 0.733, the composition are (Zn_0.15Nb_0.3Ti_0.55)O₂, SmNbO₄, SmTiNbO₆. When x is bigger than _0.5 there is no longer ZnNb₂O₆. And theÏ„_f of the ceramics changed from negative to positive with x is bigger and bigger. So ZnTiNb₂O₈ is used to instead of ZnNb₂O₆ in order to get a microwave ceramics which have near zeroÏ„_f. For (1-x)ZnTiNb₂O₈- xSmTiNbO₆ ceramics, the ceramics have very good microwave properties( r = 24.63, Q^*f=11846GHz,Ï„_f = 0.16ppm/℃) when x is _0.35. But the sintering temperature still be too high to co-fire with the electrode Ag or Cu and the density is not good enough. So the sintering aid are used in this composite compound in order to lower the sintering temperature, increase the density as well as improve the microwave dielectric properties.CuO and CuO-ZnB are added into the composite ceramics seperately as the sintering aids in order to lower the sintering temperature. The sintering behavior and microwave properties are investigated, and the results are shown as followed. The best microwave properties of (1-x)ZnTiNb₂O₈- xSmTiNbO₆ composite ceramics are r = 36.57, Q* ? =17793GHz,Ï„_f =1.2117ppm/℃when x is _0.35 and sintering temperature is 1125℃. At this time, _0.5wt% CuO is added as the sintering aid. In this process CuO reacted with the base elements and there was no liquid phase being observed. So it belongs to solid state sintering mechanism. For CuO/ZnB, when CuO and ZnB glass are 3wt% and 1wt%, sintering temperature is 950℃and x is 0.73 the (1-x)ZnTiNb₂O₈-xSmTiNbO₆ composite ceramics reach the best microwave properties (ε_r = 35.67, Q^*f=13710GHz,Ï„_f =5.38pm/℃). In this process there is liquid phase being observed so it belongs to liquid sintering mechanism.