Preparation And Properties Of CaMgSi₂O₆ Based Microwave Ceramics

Microwave dielectric ceramics always play a significant role in microwave applications due to their ideal microwave dielectric properties.CaMgSi₂O₆ ceramics have low dielectric constant??_r=7⁸?,which can be used for millimeter wave communication and also as substrates material for microwave integrated circuits.Therefore,it has been widely studied at home and abroad.However,the low quality factor?Q×f?,negative temperature coefficient of resonant frequency??_f?-45ppm/??and relatively high sintering temperature?S_T?1300??would hinder the further application of CaMgSi₂O₆ ceramics in microwave field.On the premise that the?_r values of CaMgSi₂O₆ ceramics does not fluctuate much,four cations Mn²⁺,Ni²⁺,(Mn_1/2Zn_1/2)²⁺and Cr³⁺were used to substitute for Mg²⁺to improve the Q×f value;CaTiO₃ ceramics and CaMgSi₂O₆ ceramics have formed a composite to adjust the?_f value;BaCu?B₂O₅?ceramics were added as sintering aids to reduce the sintering temperature of CaMgSi₂O₆ ceramics.1.Solid-state reaction method was applied to synthesize samples.Mg²⁺was substituted with Mn²⁺,Ni²⁺,(Mn_1/2Zn_1/2)²⁺and Cr³⁺in CaMgSi₂O₆ ceramics,and the effects of four cations on phase composition,surface morphology,crystal structure and microwave dielectric properties of ceramics were studied.The experimental results indicated that only Cr³⁺formed the secondary phase Ca₃Cr₂?SiO₄?₃ in ceramics with the increase of substitutes content in the specified range,and the rest only formed solid solution.The grain size of ceramics decreased when a small amount of Cr³⁺and Ni²⁺ions were doped into the ceramics.Among the four ceramics,the?_r was mainly affected by ionic polarization and density,the Q×f values depended largely on the relative density and internal stress of ceramics,and under the influence of oxygen octahedron distortion and bond valence,the?_f values of the four kinds of ceramics drifted negatively with the increase of substitution amount.CaMg_0.98Cr_0.04/3Si₂O₆ ceramics sintered at 1270? for 3h exhibited excellent microwave dielectric properties of?_r=8.06,Q×f=89054 GHz,?_f=-44.92 ppm/?.CaMg_0.98Mn_0.02Si₂O₆ ceramics??_r=8.01,Q×f=83469 GHz,?_f=-45.27 ppm/°C?and CaMg_0.98(Mn_1/2Zn_1/2)_0.02Si₂O₆ ceramics??_r=8.16,Q×f=76184 GHz,?_f=-41.66 ppm/°C?both obtained good microwave dielectric performances when were sintered at 1300? for 3h.High microwave dielectric performances of?_r=7.76,Q×f=91302 GHz,?_f=-44.76 ppm/°C were achieved when the CaMg_0.95Ni_0.05Si₂O₆ ceramics sintered at 1290? for 3h.2.The?_f values and sintering temperature of CaMgSi₂O₆-based microwave ceramics were adjusted by two-phase composite and low melting point oxide doping.CaTiO₃ ceramics were doped into CaMg_0.98Cr_0.04/3Si₂O₆ ceramics.The phase composition,microstructure and microwave dielectric properties of the two-phase ceramics were explored.According to results of XRD,both CaMgSi₂O₆ and CaTiO₃phases existed in the composite ceramics.The apparent density and?_r of CaMg_0.98Cr_0.04/3Si₂O₆-yCaTiO₃?0.03?y?0.15?ceramics increased with the increase of CaTiO₃ content.Under the impact of lattice defects,the Q×f values of ceramics sintered at 1260? with four different components decreased with the increase of CaTiO₃ content.The?_f values of ceramics were effectively compensated and drifted to zero with the increaseof CaTiO₃ content.The microwave dielectric properties of CaMg_0.98Cr_0.04/3Si₂O₆-0.15CaTiO₃ ceramics sintered at 1260? are as follows:?_r=10.24,Q×f=33417 GHz,?_f=-5.93 ppm/?.Low melting point oxide BaCu?B₂O₅?can significantly reduce the densification temperature of CaMgSi₂O₆ ceramics.When the sintering temperature dropped to 1050?,CaMgSi₂O₆ pure phase was synthesized in all four components.The dielectric loss of CaMgSi₂O₆+3wt%BaCu?B₂O₅?microwave ceramics was the lowest among the four components:?_r=7.84,Q×f=24422 GHz,?_f=-39.51 ppm/?.