| In recent years, the rapid development of the communication industry puts forward further requirements for the performance of the microwave dielectric ceramic materials and promotes the rapid development of microwave dielectric materials. Moreover, the study on microwave dielectric ceramic materials for LTCC applications is also a hot issue in the industry. In addition, few people have investigated dielectric properties of ZnO-MnO2 based ceramics. So the influences of the Zn/Mn ratios, ion substitution, and sintering aids on phase structure, reaction mechanism, and microwave dielectric properties of ZnO-MnO2 based ceramics prepared by solid-state sintering method were investigated. Lastly, the tape casting properties and co-firing matching characteristics with silver of ceramic powder were also studied.First, the phase compositions of the different proportion zinc manganese ceramic materials were studied. The XRD results showed that the main crystal phase of the ceramics was ZnMn2O4 spinel-like phase. That is to say, compared to ZnMnO3 and ZnMn3O7,ZnMn2O4 was more stable. Thus, the corresponding oxide ceramics such as ZnMnO3 and ZnMn3O7 could not be synthesized by simply controlling the ratio of ZnO and MnO2 powders. When the ratio of zinc and manganese was 1:1 and 1:2, there was a small amount of ZnO remaining in the ceramic. However, for 1:3, 1:4, 1:5 and pure MnO2, the ceramics were single phase ZnMn2O4 with spinel-like structure. Therefore, a reaction model of zinc manganese for core-shell structure was proposed, which ZnO and MnO2 core formed ZnMn2O4 based spinel-like phase. During the heating process, MnO2 was transformed into Mn2O3 and Mn3O4 successively, which formed the solid solution of ZnMn2O4 and(Zn, Mn)Mn2O4. But(Zn, Mn)Mn2O4 solid solution hindered the diffusion of ZnO particles into the core, so excess ZnO phase in ZM11 and ZM12 ceramics was detected. In addition, the increase of MnO2 content and the prolongation of the dwelling time were beneficial toforming a single ZnMn2O4 based spinel-like phase.The microwave dielectric properties of the ceramics with different Zn/Mn ratio were studied. The relatively dense ceramics sintered at the 1450 °C could be obtained.Microwave dielectric properties couldn’t be achieved until ZnO-free second phase because of the large dielectric loss of ZnO. As the Mn content increased, the grain size, the density,εr and Q×f value rose initially and then dropped, while τf reduced gradually along the negative direction. The ZnO: 3MnO2(ZM13) ceramic showed relatively good microwave dielectric properties: εr=8.1, Q×f=14209 GHz,τf=-69.2 ppm/°C.The variation of phase compositions, microstructures and microwave dielectric properties of Zn(Mn1-xTix)3O7(ZMT) ceramics and effect of sintering aids on sintering temperature were investigated. The results showed that the phase compositions of ZMT ceramics were closely related to x values. The end members exhibited single ZnMn2O4spinel-like phase for x=0, and Zn2TiO4 and rutile mixtures for x=1. In addition, pure ZnTiO3 solid solution for x=0.6 and the rutile second phase along with the ZnTiO3 solid solution for x=0.8 were observed. As x increased, εr increased initially to a maximum value of 33.08 at x=0.8 and then decreased, whereas Q×f increased slightly, and τf changed gradually from negative to positive values. In addition, both the partial substitution of Mn by Ti and the addition of ZBG effectively reduced the sintering temperature.Further tape casting characteristics and co-firing matching behaviors with silver electrode of ZBG-doped ZMT ceramic powder were investigated. The 5 wt.% ZBG-doped ZMT(x=0.68) ceramics can be sintered well at 900 °C and exhibited excellent microwave dielectric properties(εr=18.2, Q×f=12018 GHz, τf =- 3.98ppm/°C) and good co-firing compatibility with silver electrode, which could be a promising LTCC material. |
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