| Microwave dielectric ceramics(MDCs)are key passive components in wireless communication equipment,which have the advantages of low cost,high stability,high efficiency and ease of use.The key quality factors of MDCs are the appropriate relative dielectric constant(εr),high quality factor(Q×f)and resonant frequency temperature coefficient(τf).However,relevant research has proved that these three parameters restrict each other,and the optimal MDCs that can meet these three characteristics at the same time are very limited.Therefore,it is of great significance to study microwave dielectric ceramic materials with excellent performance to improve and enhance material functions.In recent years,the continuous development of the Internet of Things(IoT)and the fifth generation mobile communication network(5G)have provided a strong driving force for the research and development of MDCs.A2BO4 type silicon zinc ore is actively studied because of its super high Qxf value and low relative dielectric constant,and is widely used in the field of microwave communication.In this paper,Zn2GeO4 microwave dielectric ceramics with low dielectric constant were studied by doping A/B sites and adding sintering additives to reduce sintering temperature.The effects of phase composition,crystal structure,micro morphology and density on dielectric properties were investigated by X-ray diffraction(XRD),scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS)and Rietveld finishing.Main findings:(1)A series of Zn2+0.5xGe1-xGaxO4(0.1≤x≤0.4)ceramics were prepared by the traditional solid state sintering method.XRD and Raman spectra showed that the moderate doping of Ge by Ga could inhibit the existence of ZnO phase detrimental to dielectric properties.In the x=0.1 and 0.2 components,Zn2GeO4 was the main phase,while in the x=0.3 and 0.4 components,ZnGa2O4 was the main phase.The shift of diffraction peaks indicated that Ge4+and Ga3+were fused,the change of Raman spectrum intensity also reflects the increase/decrease of the amount of ZnGa2O4/Zn2GeO4,which is consistent with the XRD results.The moderate substitution of Ga for Ge induced a low loss ZnGa2O4 phase,which was confirmed by XRD,SEM and Raman spectroscopy.With the increase of doping content,the phase percentage of ZnGa2O4 phase increases and becomes dominant(-69%)after x=0.3.Based on the mixing rule,the relative dielectric constant and quality factor are improved.In the combination of x=0.4,we can obtain the dielectric properties combination of εr～9.4,Q×f～97,000 GHz and τf～-30.7 ppm/℃,which is related to the superior dielectric properties of ZnGa2O4 compared with Zn2GeO4.(2)A series of Zn2-xCuxGeO4(0.02≤x≤0.08)ceramics were prepared by traditional solid state sintering method.XRD spectra and Rietveld finishing showed that the main phase was Zn2GeO4 when doping amount x=0.02,but a small amount of second phase ZnO appeared.With the increase of doping amount x,pure Zn2GeO4 phase was generated,indicating that a certain amount of Cu2+doping can inhibit the generation of second phase ZnO.When x=0.08,the doping amount reaches the solution limit,because when x>0.08,CuZnGeO4 phase appears at 2θ=35.7°.The SEM test results of ceramic samples show that the decrease of ceramic sintering temperature by CuO can significantly help and improve the ceramic grain growth and density.It can be considered that CuO is a good sintering aid.When the sintering temperature is 1010℃ and the doping amount x=0.08,the dielectric properties of the ceramics are the best:τf～13.88 ppm/℃。(3)A series of Zn1.92Cu0.08GeO4-y wt%B2O3(0.25≤y≤1)ceramics were prepared by traditional solid state sintering method,and the compatibility of Ag electrode with Zn1.92Cu0.08GeO4-0.5wt%B2O3 ceramics was studied.The XRD spectrum shows that the formed phase is Zn2GeO4 pure phase and no other second phase is formed.The SEM morphology shows that B2O3 as sintering additive can reduce the sintering temperature of ceramics,and the grain size is smaller than that of pure phase Zn1.92Cu0.08GeO4 ceramics at low temperature.At the same time,it is believed that liquid phase is formed in Zn1.92Cu0.08GeO4 ceramics added with B2O3.The density of ceramics will be affected by the sintering in liquid phase environment,and the proper amount of liquid phase in the process of liquid phase sintering is conducive to improving the dielectric constant,and the quality factor Q×f.Zn1.92Cu0.08GeO4-0.5wt%B2O3 ceramics sintered at 940℃ showed good microwave dielectric properties:τf～-25.3 ppm/℃.At 940℃,Zn1.92Cu0.08GeO4-0.5wt%B2O3 ceramics can be co fired with Ag.XRD,SEM and EDS tests show that co-fired does not react with Ag,indicating that Zn1.92Cu0.08GeO4-0.5wt%B2O3 ceramics may be used as LTCC in reality,and as LCTT substrate candidate materials,it also has good dielectric properties and can be used as materials for exploring and designing LTCC filters. |
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