Preparation Of ZnTiNb 2 O 8 Based Ceramics By Reaction Sintering Method And Its Microwave Dielectric Properties

Microwave dielectric ceramic is the key material to the microwave devices, and the development level of microwave communication technology depend on its performance. ZnTiNb₂O₈ ceramic is an excellent microwave dielectric ceramic with moderate relative permittivity constant ?34? and high Qxf value ?42,500GHz?. The sintering temperature of ZnTiNb₂O₈ ceramic is high and pure phase is difficult to synthesize using the conventional solid state method; with wet chemical method, precursor powder particles with high active can be produced, while, the preparation process is complex and not easy to control. The shortcoming in preparation process of ceramics have been seriously restricted the commercial application of the ZnTiNb₂O₈.This paper selected ZnTiNb₂O₈ ceramics for the study. The ZnTiNb₂O₈ ceramics were prepared by reaction sintering process and conventional solid state method, respectively. The influences of different processes on sintering ability and the microwave dielectric properties were compared. Secondly, using reaction sintering method, the proportion of TiO₂ within the raw materials have been used to adjust the temperature coefficient of resonator frequency to nearly zero; then the sintering additive CUO-V₂O₅ were added to the above composite ceramics, reducing the sintering temperature to meet the requirements of LTCC technology. The specific research contents and results are as follows:?1? The ZnTiNb₂O₈ ceramics were synthesized through reaction sintering process ?RS?and conventional solid state method?SS?. The pure phase ZnTiNb₂O₈ ceramics were prepared sintered at 1,000??1,150? by the two methods. Both the relative densities of these two groups reached the maximum values sintered at 1,075?, RS group with 97.92%, and SS group with 98.88%. The grains were difficult to grow for RS group ceramics since calcination step was bypassed, so that sintered at the same temperature, the average grain size of SS group was bigger than that of the SS group. The relationships between the dielectric constant values ?Qxf values? and sintering temperature followed the similar trend to those between density and sintering temperature, and sintered at 1,075?, the microwave dielectric properties of the two groups exhibited the optimum values:RS group with ?r= 34.5, Q×f=55,500 GHz, ?f=-61 ppm/?, and RS group with ?r= 34.1, Q×f= 53,300 GHz, ?f=-68 ppm/?, respectively. The ZnTiNb₂O₈ ceramics with lower sintering temperature and excellent microwave dielectric properties were obtained by the two methods in this paper. The ceramics of the two groups had no significant difference in performances. While ceramics prepared by RS, which is characterized by easy operation, less environmental pollution, and suitable for large-scale commercial production, thus reaction sintering process is an effective method for ZnTiNb₂O₈ ceramics preparation.?2? The ZnO-Nb₂O₅-xTiO₂ ?1?x?2? ceramics were prepared by reaction sintering process. With excess TiO₂ addition, the temperature coefficient of resonator frequency of the ceramics was likely to adjusted to nearly zero. The phase structures and phase content changed with increasing sintering temperature and TiO₂ content. Thus, the microwave dielectric properties of ceramics were consisent with sintering ability and second phase content. The second phase Zn_0.17Nb_0.33Ti_0.5O₂ deteriorated the Q×f values of the ceramics, while increased the dielectric constant and adjusted the temperature coefficient of resonator frequency to near-zero. The excellent microwave dielectric properties were obtained for ZnO-Nb₂O₅-2TiO₂ ceramics sintered at 1,075? for 5 h:?r = 45.3, Q×f= 23,500 GHz, ?f=+4.5 ppm/?.?3? CuO-V₂O₅?CV? were selected as sintering additives to lower the sintering temperature of ZnO-Nb₂O₅-2TiO₂?ZTN? composite ceramics. Both the sintering temperature and sintering additives content could influence the content of two phase and the grain growth situation, which ultimately affect the microwave dielectric properties of ceramics. ZTN ceramics with 1.5 wt% CV and sintered at 950? had excellent microwave dielectric properties of ?r=45.9, Q×f=12,200 GHz, ?f= - 1.8 ppm/? The liquid phase was found at the boundary of grains, which indicated that CV acts as a liquid phase to enhance the sinterability of the ZTN ceramic. The XRD pattern of ZTN-1.5 wt% CV additive co-fired with 20 wt% Ag powders at 950? demonstrates that CV-added ZTN ceramic by reaction-sintering process was able to match with the Ag electrode well.