Study On The Preparation And Properties Of Molybdate Based Low-Temperature Firable Microwave Dielectric Ceramics

As an important technological approach to realize miniaturization and modularization of devices,microwave dielectric ceramic has becomed a hot research topic in the field of dielectric materials.Through constant research and study,several novel low-temperature firable microwave dielectric ceramics were successfully parpeared and the relationship between fabrication process、phase structure、microstructure and microwave dielectric properties were systematically investigated by XRD,SEM,EDS and vector network analyzer.The main contents of this paper are listed as follow:First,through conventional solid-state method,novel molybdate based microwave dielectric ceramic Y₂Mo₄O₁₅ was synthesized at low temperatures.The XRD and refmement results indicated that Y₂Mo₄O₁₅ was single-phase ceramic and belonged to hexagonal system with a space groupP21/c.The SEM result exhibited dense and uniform microstructure,which indicated Y₂Mo₄O₁₅ could be well sintered at low temperature.The variation ofε_r of Y₂Mo₄O₁₅ ceramics as a function of sintering temperature kept consistent with that of relative density,while Qxf affected by both the relative density and packing fraction.As no structural changes,theτ_f of Y₂Mo₄O₁₅remained relatively stable.At the sintering temperature of 700 ^oC,Y₂Mo₄O₁₅ achieved the best microwave dielectric properties:ε_r⁸.2,Qxf⁷8,148 GHz,τ_f^-49.2 ppm/^oC,which made it has large potential in LTCC application.Then,a new series of microwave dielectric ceramics Ln₂Zr₃（MoO₄）₉（Ln=La,Sm,Nd）were successfully synthesized by solid-state method.The XRD results indicated they have same phase structure and belonged to trigonal system with a space group R^<sub>3c.La₂Zr₃（MoO₄）₉,Sm₂Zr₃（MoO₄）₉,Nd₂Zr₃（MoO₄）₉ obtained the best dielectric properties ofε_r¹0.8,Qxf⁵0,628 GHz,τ_f^-38.8 ppm/^oC;ε_r¹1.0,Qxf⁷4,012GHz,τ_f^-45.3 ppm/^oC;ε_r¹0.8,Qxf⁵8,942 GHz,τ_f^-40.9 ppm/^oC at 775^oC、875^oC、900^o C,respectively.Owing to same structure of them,ε_r andτ_f have no obvious difference.But,intrinsic factors mainly resulted in the difference of Qxf,higher packing fraction,higher Qxf value.At last,new microwave dielectric ceramics Li₃Ba₂La_3（1-x）Y_3x（MoO₄）₈（0.0≤x≤1.0）were successfully synthesized,and we also investigated the effect of A-site substitution on the structure and microwave dielectric properties of Li₃Ba₂La_3（1-x）Y_3x（MoO₄）₈.The XRD results exhibited that the the diffraction peak gradually moved to higher angle with the increase content of Y³⁺,which indicated the cell volume gradually decreased for the smaller ion radius of Y³⁺.The increasing packing fraction with the increase Y³⁺content resulted in the increase of Qxf.In addition,the bond valance of Ln site of Li₃Ba₂La_3（1-x）Y_3x（MoO₄）₈ ceramics decreased with increasing x values,which madeτ_f gradually moved to the positive direction and finally obtained the best perfoamances at x=0.4:ε_r¹4.4,Qxf¹4,994 GHz,τ_f⁺6.9 ppm/°C.Moreover,Li₃Ba₂La_1.8Y_1.2（MoO₄）₈ has good chemical stability with Ag,which indicate it could be actual y applied in LTCC.