Research On Low Temperature Sintering Of(Ca_0.9375Sr_0.0625)_0.3(Li_0.5Sm_0.5)_0.7TiO₃Microwave Dielectric Ceramics

In recent years, with the rapid development of microwave communication technology, the research and development of microwave dielectric ceramics which can be co-sintered at low-temperature with Ag or Cu and other low melting point conductor metals have become a focus and direction. In this dissertation, the (Ca0.9375Sr0.0625)0.3(Li0.5Sm0.5)0.7Ti03(CSLST) microwave dielectric ceramics material with high dielectric constant was selected as the research objects. Using low melting point oxide and glass as sintering additives, the effects of different sintering aids on sintering characteristics, phase compositions, microstructures and dielectric properties of microwave ceramics were studied. The low-temperature sintering properties and mechanisms of the microwave dielectric ceramics were researched. The sintering behavior when co-fired with electrode Ag was investigated. It is proved that the CSLST ceramics may be the promising candidates for LTCC applications.The low-temperature sintering properties of CSLST microwave dielectric ceramics were researched by using composite compound B2O3-CuO-Li2CO3(BCL), BCL glass with different compositions, the composite of BCL glass and Bi2O3as sintering additives. The results indicate that the major phase of additives-doped ceramics is orthorhombic perovskite by XRD analysis.(1) The sintering temperature of CSLST ceramics is reduced by325℃using1.0～10.5wt%BCL composite compound as sintering additives, when the BCL addition amount is greater than7.5wt%, the secondary phase of Cu3Ti3O is detected. The sample of CSLST with5.5wt%BCL sintered at925℃for5h has excellent dielectric properties:dielectric constant εr=86.7, quality factor Q×f=2267GHz, resonance frequency temperature coefficient τf=29.3×10-6/℃.(2) The softening temperature of BCL glass is different when the composite is M(B2O3-CuO):M(Li2CO3)(M BC:MLi)=2.5-20:1(in mass), and the effect of wetting to the CSLST ceramics substrate is different too, when the composition is MBC:MLi=10:1, the wetting effect is best. The sintering temperature of CSLST can effectively decreases from1250℃to900℃with5.5～15.0wt%BCL glass additives, meanwhile, the secondary phases of Cu3Ti3O and CaCu3Ti4O12are detected(except M BC:MLi=2.5:1). Although with different content of BCL glass, the same secondary phases are detected when the composite is M BC:MLi=10:1. The sample of CSLST with12.5wt%BCL glass which the composite is M BC:M Li=10:1sintered at900℃for5h has the best dielectric properties:εr=77.7, Q×f=1845GHz, τf=21.35×10-6/℃.(3) Using the optimum composite of BCL glass and different amount of oxide Bi2O3as composite sintering additive, the sintering temperature of CSLST ceramic can effectively decrease to875℃with12.5wt%BCL glass and1.0～ 4.0wt%Bi2O3. When the Bi2O3addition amount is0～1.0wt%, the secondary phases Cu3Ti3O and CaCu3Ti4O12are detected. However, when Bi2O3addition amount is greater than2.0wt%, the secondary phases are not detected. With the increasing of Bi2O3content, the τf decreases positive values to negative values. The sample of CSLST with12.5wt%BCL glass and2.0wt%Bi2O3sintered at875℃for5h exhibites excellent dielectric properties:εr=78.9, Q×f=1852GHz, τf=3×10-6/℃A series of microwave dielectric ceramics with excellent dielectric properties would be achieved, which meet LTCC technology, based on the research of the low-temperature sintering of CSLST ceramics.